Atomic, Molecular and Optical Physics Seminar

The low mass star formation process is well studied, and the evolution process is comparatively well established. But, it is still unclear whether the massive star also follows a similar process or it goes through a completely unconventional way. In this attempt, we made a detailed observational analysis of a well-known hot molecular core lying in the high-mass star-forming region G31.41+0.31 with the ALMA. We observe an inverse P-Cygni profile (representative of the infalling envelope) towards this source. Many other complex organic molecules are also observed towards this source. In my presentation, I will explain this source's detailed radiative transfer modeling to explain the observed line profiles.

Quantum repeaters are indispensable for high-rate, long-distance quantum communications. The vision of a future quantum internet hinges strongly on realizing quantum repeaters in practice. Numerous repeaters have been proposed for discrete-variable (DV) single-photon-based quantum communications. Continuous variable (CV) encodings over the quadrature degrees of freedom of the electromagnetic field mode offer an attractive alternative. For example, unlike DV, CV transmission systems do not involve single-photon detectors and hence are easier to integrate with existing optical telecom systems. Yet, repeaters for CV have remained elusive. We present a novel quantum repeater scheme for CV entanglement distribution over a lossy bosonic channel that beats the direct transmission exponential rate-loss tradeoff. The scheme involves repeater nodes consisting of a) Einstein-Podolsky-Rosen entanglement sources that generate CV entanglement in the form of two-mode squeezed vacuum (TMSV) states, b) the quantum scissors operation to perform nondeterministic noiseless linear amplification of lossy TMSV states, c) a layer of switched, mode multiplexing inspired by second-generation DV repeaters, which is the key ingredient apart from probabilistic entanglement purification that makes DV repeaters work, and d) a non-Gaussian entanglement swap operation. We present our exact results on the rate-loss envelope achieved by the scheme.

hree decades ago, in a celebrated work, Zak is credited to have found the geometric phase acquired by an electron in a one-dimensional periodic lattice as it traverses the energy band. It was found that such a geometric phase characterizes the topological state of the system and determines its electric polarization. Unfortunately, the expression given by Zak yields an arbitrary value for the geometric phase, which depends upon the choice of convention employed in expressing it. We rectify this gross error by providing a correct and consistent expression for such a geometric phase, which we call the Pancharatnam-Zak phase. In this talk we shall see that the Pancharatnam-Zak phase is a quintessentially geometric object, displaying gauge and reparametrization invariance, and correctly classifies the energy bands of the lattice. A filled band generalization of the Pancharatnam-Zak phase is also constructed and shall be discussed in the talk.

Quantum technology is a fast-growing field of physics and engineering, which utilizes fundamental properties of quantum mechanics to enable new applications such as long-distance secure communication and metrology with sensitivity beyond classical limits. Currently, these technologies are available at visible, near-infrared (NIR) and telecom wavelengths but are strongly underdeveloped at longer wavelengths. There is a growing interest to deliver sources and detectors operating in the infrared, for various applications such as daylight satellite-to-ground and satellite-to-satellite based quantum communications, and future interferometric gravitational waves detection in LIGO experiments. In this talk, I am going to present the generation and characterization of a pulsed spontaneous parametric down-conversion photon pair source at 2.080 μm. The characterization includes the efficiency estimation of the crystal, coincidence-to-accidental ratio determination, estimation of quantum efficiency of single photon detectors at 2.080 μm, the two photon Hong-Ou-Mandel interference, and polarization entanglement

Starting from Einstein's paper ( Can Quantum-Mechanical Description of Physical Reality Be Considered Complete? 1935), I will explain, why Einstein concluded that the quantum theory to be incomplete using an example of a compound system which we now call as the entangled system and introduced the hidden variable theory in attempt to replace the quantum mechanics. Later, in 1964 John. S. Bell showed that the predictions of the hidden variable theory are incompatible with the predictions of quantum mechanics. Clauser and his colleagues generalized the inequality shown by Bell and formulated the new inequality known as Bell's inequality. Violation of this inequality gives an indication of the presence of nonlocal correlations (Quantum Entanglement) that exist between two subsystems.

We report the first realization of χ(3) QPM THG in isotropic polymer films with alternatingly deposited multilayers of a highly nonlinear organic material and a passive polymer material. The phase mismatch created in the highly nonlinear medium was compensated in the passive medium. We also could demonstrate fast and wide wavelength tuning of a ns-optical parametric oscillator (OPO) based on 3-segment PPLN device. The first segment generated the ultra-broadband signal and the idler bands and the third segment amplified the selected wavelengths of the ultra-broadband gain. This wavelength selection could be electro-optically (EO) controlled by applying a dc electric field to the middle segment.

Indistinguishability is a profound feature in the quantum world. In order to meaningfully describe a bipartite entangled state of two identical, indistinguishable particles, at least two variables are required. One variable A is used to label the particles while the entangled is observed in another variable B ([A,B] = 0). Hence two identical particles can be shown to be entangled in one variable or the other depending upon which variable is being used to distinguish the photons. Thus just the distinguishability reveals the entanglement. This property is called entanglement duality. In this talk, I discuss about how the entanglement present in two independent variables (polarization and orbital angular momentum (OAM)) of a pair of indistinguishable photons gets revealed as they are separated in one of the variables.

In this talk, I will discuss about the generation of vector vortex beams using polarization sensitive spatial light modulator along with their scattering. We compare the results with the scalar vortex beams.

In this presentation, we introduce a novel quantum key distribution protocol, coincidence detection quantum key distribution protocol (CD BB84-QKD). We show that in this protocol Poissonian nature of weak coherent pulses instead of posing a security risk can be used to the advantage for achieving secure key rate over a longer distance as compared to standard decoy state quantum key distribution. This protocol will also be able to track the presence of Eve (Eavesdropper) from the multi-photon (mainly consisting of two and three photons) coherent weak laser pulses. We show that, using this method the key rate can also be increased as some of the multi-photon pulses will contribute to the final key.

The interaction of intense femtosecond pulses with atoms and molecules gives rise to new phenomena like multiphoton ionization (MPI), above threshold ionization (ATI), and tunnelling ionization (TI). ATI has been well investigated both theoretically and experimentally in atoms, where an electron absorbs energy higher than the threshold energy required for it to be removed from the atom. Similar process has been predicted in molecules and it is called above threshold dissociation (ATD). In this case, a molecule absorbs energy higher than the threshold energy required for it to dissociate. The bond breaking and bond formation in time domain is not well studied as this process occurred in ultrafast timescale ranging from picosecond to femtosecond. In this seminar, I shall discuss these processes, in particular ATD, chemical control and the time-resolved dissociation reactions.

Light carrying orbital angular momentum (OAM) generally known as optical vortex, find many application in optical tweezers and optical communication. Unlike the polarization of light, which offers a two dimensional Hilbert space, the OAM of photon provide an infinite-dimensional Hilbert space. The higher dimensional OAM correlations realized using spontaneous parametric down-conversion (SPDC) process is generally restricted to a sub-space of single OAM. This is due to the pump carrying a single OAM value. Access to other OAM sub-space can be realized by pumping with the superposition of optical vortex beam. I also talk about the quantum nature of SPDC with Hong Ou Mandel interference.

Chasing the electron and nuclear dynamics in atoms and molecules will facilitate in controlling the process. Ultra-short femtosecond pulses have become the key tool for chasing the dynamics and also controlling the reaction dynamics. In polyatomic molecules, at certain energies Born-Oppenheimer approximations break down. These regions of interest (Conical Intersections) are rich in fundamental physics, which when explored not only gives the reaction dynamics but also can be used to explore the quantum mechanics at an experimental level. Probing the wave packet dynamics near conical intersection is not straight forward. We are going to align the molecules and probe the wave packet near conical intersection. In this seminar, I will be addressing the concept of Molecular alignment on a theoretical platform with computational tools and solve the Time Dependent Schrodinger Equation.

For an entangled state of two photons, the probability of detecting the two photons in a given state, cannot be written as the product of individual probabilities of each photon. This is known as non-separability. Non-separability is not only an intrinsic nature of the quantum system but classical light beam can also be shown to possess non-separability, albeit between different degrees of freedom. The classical analogy of quantum entanglement is studied using a laser light beam, which is prepared in a non-separable state of different degrees of freedom (polarization and orbital angular momentum). However, the analogy fails to produce effects of quantum nonlocality. It must be emphasized that Bell's inequality was introduced to measure nonlocal entanglement between two quantum systems. In the present talk, I will discuss classical and quantum non-separable states, their generation and analysis.

It is assumed that an electron can also have finite electric dipole moment (EDM) as its another intrinsic property like its mass or charge. The EDM of an electron can arise due to simultaneous violations of parity (P) and time reversal (T) symmetries. However,its Standard Model predicted value differs by several orders compared to other models of elementary particle physics. Direct observation of EDM of a single electron is impractical. Therefore,atoms or molecules are used as a means of its detection. In this talk, I shall demonstrate the triatomic molecule HgOH as one of the most promising candidates for electron EDM experiment. In this context, I shall also discuss about roles of studying permanent electric dipole moment and static electric dipole polarizabilities of molecule.

In 1950's, Miller's experiment on biomolecule (amino acids) synthesis from prebiotic soup revolutionized our understanding on the Origin of life. Carl Sagan et al., in 1970 showed shock processing of simple molecules (ammonia, methane, water etc..) was also a pathway to the formation of amino acids in extreme conditions. Later, since 2000, the astrochemical ices containing simple and complex (purine and pyrimidine) molecules subjected to UV and charged particle irradiation were reported to synthesize amino acids and even nucleobases. However, the fate of biomolecules subjected to extreme conditions are to-date least understood. Recently, we have overcome the experimental limitations and observed complex macroscale structures in shock processed biomolecules. The results suggest the thread like features, so far, reported in meteorites are rather assemblages of biomolecules. In this talk, I will cover our efforts to understand the fate of biomolecules in extreme conditions and the preliminary results.

Fluorescent point-defect centers in diamond, especially nitrogen vacancy (NV) center in diamond, have been widely exploited as a potential solid state spin-qubit system which has significantly boosted up research on quantum technology. There is a constant effort on standardizing the experimental protocols to manipulate the NV spins in a controlled fashion. On the other hand, research works have been devoted on optimizing the preparation procedure which can produce defect centers with superior optical properties, controllable spin states and that can be prepared in a reproducible manner. Through this presentation we will demonstrate a few important experimental progresses both in the direction of optimizing of quantum controlled experiments, and spectroscopic characterization of NV centers which are suitable for applications in quantum technology. In addition, our ongoing experimental efforts to explore new quantum defect centers will also be discussed.

The parity (P) and time reversal (T) violating electric dipole moment of the electron (eEDM) is an extremely important non-accelerator probe of particle physics, and is also relevant to our understanding of the matter-antimatter asymmetry in the universe. This particle physics property can obtained by measuring a shift in the energy of a molecule in some state due to the eEDM, and combining it with a quantity that can only be calculated using relativistic many-body theory, the effective electric field (Eeff). The eEDM has not yet been detected; the best upper bounds have been obtained using ThO, followed by HfF+ and YbF. Advances in experimental techniques, as well as search for better molecular candidates, therefore, become imperative to probe new physics. In this presentation, we shall discuss our work, where we propose mercury alkalis (HgLi, HgNa, and HgK) as promising eEDM candidates, based on both theoretical as well as experimental considerations. We find that these reasonably large values of Eeff, in combination with attractive experimental features, lead to estimated sensitivities of ~10-30 e-cm, which is an order of magnitude better than the current best candidate, ThO. We shall also discuss our results of our calculations on the triatomic system, YbOH, on which an experiment has just commenced.

Photons with orbital angular momentum can be used for encoding information beyond one bit per single photon. This provides a great resource for the study of various fundamental properties of nature as well as utilise these properties for carrying out certain quantum information tasks. Also, photons with orbital angular momentum represent higher dimensional quantum systems or qudits. In this talk, we will discuss the generation and entanglement of photons produced by spontaneous parametric down conversion in the orbital angular momentum basis. We will also discuss the possiblity of using orbital angular momentum of the photons along with polarization for generating hyper and hybrid entangled quantum states.

Photonic waveguides have emerged as an ideal system for the study of quantum optical effects. In addition, they find interesting applications in quantum information science. I will describe my work on the transport and quantum walk of light in optical waveguides.

A novel table-top Laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy hybrid system have been developed using a single pulsed Nd:YAG laser and a high-resolution ICCD coupled echelle spectrograph for more advanced material characterization. The complimentary elemental and molecular information of the analyte provides comprehensive information about the sample and help to omit the ambiguity while explain the inherent properties of the materials. The synergy between LIBS and Raman data has been successfully used for the analysis of clinical samples (kidney stones, teeth), plastics, chemicals, minerals, archeological samples, etc. The feasibility of collecting information from a remote distance has also been investigated using the combined measurements. The developed hyphenated remote LIBS-Raman system has been tested for security and mineralogical applications.

Development of coherent sources of laser radiation in mid-infrared (mid-IR) spectral domain is of major interest due to variety of applications ranging from remote sensing to optical communication. The advent of mid-IR sources, together with the spatial shaping into optical vortex profiles have led to interesting applications in the field of material lithography, studying chiral materials, microscopy etc. Optical vortices are beams with helical phase variation along propagation direction. Such beams have azimuthal phase variation represented by exp(ilθ), where l is the topological charge or order of the vortex. However, generation of optical vortices with wide wavelength coverage and high output power in ultrafast temporal domain requires exploration of alternative techniques. In this talk, I will present ultrafast optical parametric oscillators (OPOs) as a robust source of optical vortices in mid-IR spectral region. I will discuss challenges in designing such sources and performance of a vortex pumped picosecond OPO in mid-IR region up to 4035 nm.

Integrated optics platforms are widely explored nowadays for implementing different quantum information protocols and quantum optics experiments. In comparison to their bulk counterparts, on-chip circuits offer advantages in terms of scalability, reconfigurability and phase stability. In addition, integrated waveguides also offer higher non-linear interaction strengths and different degrees of freedom for quantum state preparation. With this motivation, several examples of on-chip linear optical networks based on different material platforms have been used to implement various quantum optics experiments such as bosonic transport simulations on silicon-on-insulator [1], universal linear optics circuit on doped silica [2] and so on. In this talk, I will focus on a few of such waveguide devices for state preparation and our recent work on an 8 x 8 reconfigurable transformation circuit which acts as an optical photonic processor based on Si3N4 waveguides [3]. The advantage of this platform compared to others is the unique combination of high index contrast, enabling a dense waveguide arrangement, ultra-low straight-propagation loss and offers spectrally wide transparency range. In addition, the device is reprogrammable, remotely controllable, and enables any 8x8 transformation. Our preliminary single photon experiments on this device, illustrates strong potential of this platform for quantum information processing protocols and quantum technologies. If time permits, I will also introduce my work on light-matter interaction in metastable helium vapours for optical memories and parametric amplification based on coherent population oscillations. [1] N.C. Harris, et al., "Quantum transport simulations in a programmable nanophotonic processor" Nature Photonics 11, 447 (2017). [2] J. Carolan et al., "Universal linear optics" Science 349 (6249), 711 (2015). [3] C. Taballione et al., "8 x 8 programmable quantum photonic processor based on silicon nitride waveguides", arXiv:1805.10999

Practical solid-state sources of tunable coherent radiation extending from the ultraviolet to mid-infrared can have an immense impact not only on the research and industry, but also on our daily life. In particular, mid-infrared wavelength range covering the molecular finger-print region is of great interest for variety of applications including spectroscopy and biomedicine. Nonlinear frequency conversion sources such as optical parametric oscillators have emerged as powerful tools, enabling access to these different spectral regions and are capable of providing broad and continuous wavelength coverage, operating in all time-scales from continuous-wave to ultrafast femtosecond regime. In this talk, I will present some of the recent advances in the development of parametric sources together with some interesting applications.

Light beams carrying both spin angular momentum (SAM) and orbital angular momentum (OAM) can be represented by mapping the total angular momentum onto a higher-order Poincare sphere. Due to their non-separable nature and infinite dimensionality in OAM degree of freedom, these beams have vast applications in optical communication. Thus it is highly beneficial to generate higher-order Poincare beams with large OAM order and at different wavelengths. However, the wavelength tunability is restricted in typical techniques to generate such beams which mainly rely on q-plates, spatial light modulators, or interferometric methods. The polarization dependence on phase matching condition makes it challenging to use nonlinear interactions of these beams to generate different wavelengths. In this talk, we present the nonlinear second harmonic generation of ultrafast, higher-order Poincare beams with large OAM orders (up to 24) at 405 nm wavelength.

The quantitative elemental estimation in rock samples is studied using Laser induced breakdown spectroscopy and in house developed the ratio-based CF-LIBS algorithm and synthetic spectrum generation methods. Main aim of this study is to estimate the accurate elemental compositions. As LIBS elemental analysis is based on some assumption such as Local thermodynamic equilibrium (LTE) conditions, optically thin, etc. the estimation by usual LIBS analysis does not give accurate elemental compositions. We have developed the ratio-based CF-LIBS algorithm as well as synthetic spectrum generation method. In synthetic spectrum method, the self-absorption effect is incorporated and results based on this is matching with the reference value obtained from the X-ray fluorescence (XRF) spectroscopy. In this seminar, I will discuss about the recent LIBS experiment on Rock samples and results. We have recently developed the Double pulse-LIBS setup in PRL and perform experiments for signal enhancement. The results on double pulse will be also discussed.

Oftentimes, in the study of molecular conformations and weak non-covalent complexes, multiple minima are encountered. Molecules may exhibit more than one conformation of nearly equal energies. Likewise, non-covalent complexes, such as hydrogen bonded complexes may manifest more than one isomeric form of the complex, with comparable interaction energies. It is a non-trivial problem to study such multiple minima systems. Moreover, the multiple-minima may have a profound influence in the chemistry of such systems and hence warrants a detailed study. In the talk, we will discuss the importance of studying such systems and the experimental methodology that is best suited for such studies, with special reference to weak intermolecular interactions and conformations.

In a broader sense, the exploitation of strange quantum mechanical phenomenon in practical applications to achieve more advantages than as usual is my interest. In this seminar, I will show that interest via both theoretical and experimental studies of quantum ghost imaging, the design of quantum microscope and theoretical studies of entanglement generation in telecommunication wavelengths. In the first part of this seminar, I will talk about quantum ghost imaging and its practical implication of a design of a quantum microscope with very high resolving power and non-invasive features. In quantum communication networks, the rules of quantum mechanics are used in practical communication networks. Quantum networks are capable of fulfilling the needs of secure networks: by using the technique of propagation of entanglement via an optical fiber link or free space, data are transferred as quantum states in these networks. For the future quantum network, it demands a highly efficient generator of entanglement states. In the final part of this seminar, I will present theoretical studies on efficient generation of entangled photon pair in the wavelength of telecommunication regime. In addition, I will talk about optical imaging through scattering media in brief.

A review of shock tubes is made based on the various modifications starting from simple shock tube to high enthalpy shock tube such as free piston driven shock tube (FPST) to produce shock waves of short duration for materials research. Shock tubes are required in various fields such as material science, astro-chemistry, astro-physics, chemical kinetics, biomedical and aerospace applications. To produce high enthalpy test gases we designed and developed material shock tubes (MST1, MST2) and free piston driven shock tube (MST3). These shock tubes are used to produce reflected shock pressure and temperature of about 10-100 bar and 1500-25000 K for 1-2 ms duration. These facilities are used to studied interaction of different types of materials with shock heated test gases in the form of pellets and fine powders. These thermodynamic conditions can be controlled by changing test gas pressure and diaphragm thickness. Application of these shock tube facilities are presented briefly for material research.

The differential optical response of a system for left and right circular polarized illumination has been widely used for the structural characterization of stereoisomers. Circular differential scattering is one of such techniques, which has become synonymous to "chiral geometry" of the system under consideration. In this talk we will discuss our recent findings claiming that even achiral structures can give raise to large differential optical response between right and left circular polarized excitation. We consider, plasmonic structure with mirror symmetry and show that the angular profile and intensity of the electric field in the farfield depends on the handedness of the circular polarized light with which it is illuminated. We investigate the individual contribution of the multipole moments to understand the source of the differential response of such achiral systems.

The demand for secure communication and high precision measurements have led to the emergence of single photon sources (SPS). Heralded single photon sources are considered as one of the most preferred SPS candidates. Incorporating the orbital angular momentum (OAM) as a degree of freedom, these single photon sources become more useful in many quantum information applications. The quantum nature of these sources is measured and characterized in terms of second order correlation function. During the talk, I will discuss the non-classical behaviour of single photons carrying orbital angular momentum. I will also discuss the analogous nature of photon OAM and number states in terms of second order correlation function.

Chemical reactions occurring on metal surfaces is a subject of wide interest, primarily because of its direct connections to heterogeneous catalyst technology. These processes are often complex and are composed of several elementary steps such as adsorption, diffusion, bond breaking/making and desorption. Moreover, each of these steps are accompanied by energy exchange with the underlying catalyst surface (often a metal) via different pathways and spanning different time scales. Understanding the energetics and dynamics of these elementary steps can have profound implications on our understanding of surface chemistry. In this talk, I will give an overview of some recent efforts in this direction especially focusing on studies involving quantum state resolved molecular beam surface scattering– experiments. Here, the incident molecules (on the target surface) are prepared in a precise quantum state distribution using a combination of molecular beam/laser pumping methods and the scattered molecules are detected using laser spectroscopy based techniques. In particular, I will discuss the case of unusually slow vibrational relaxation rate of CO on Au(111) surface,as suggested by the state resolved scattering experiments and its possible implications for reaction mechanisms in surface chemistry.

Quantum Key Distribution (QKD) is a key exchange protocol which is implemented over free space optical links or optical fiber cable. When direct communication is not possible, QKD is performed over fiber cables, but the imperfections in detectors used at the receiver side and also the material properties of fiber cables limit the long-distance communication. Free-space based QKD is free from such limitations and can pave the way for satellite-based quantum com-munication to set up a global network for sharing secret messages. To implement free space optical (FSO) links, it is essential to study the effect of atmospheric turbulence. Here, an analysis is made for satellite-based quantum communication using QKD protocols. The results obtained indicate that SARG04 protocol is an effective approach for satellite-based quantum communication.

Light carrying orbital angular momentum (OAM), generally known as optical vortex, finds applications mainly in optical tweezers and optical communication. Conventional optical vortices have their limitations in applications involving transmission of OAM modes through optical fibers, as the size of the vortex strongly depends on its topological charge, therfore, coupling to fixed core fibers becomes difficult for higher order OAM modes. A new class of optical vortex beam, termed as 'perfect optical vortex' (POV) solves the size effects of a normal vortex beam. Conventioanally, POVs are formed as a Fourier transform of Bessel-Gaussian (BG) beams. In my talk, I'll explain about the generation of heralded single photons carrying OAM (quantum twisted photons) using spontaneous parametric down-conversion. Further, I'll show that the efficiency of generated twisted photons can be improved for higher OAM values with the use of BG beams or POVs as pump. The present studies may be useful in the efficient generation of higher dimensional OAM entangled states.

One of the major mechanisms by which water molecules are formed in the interstellar medium (ISM) is via a series of ion-molecule reactions in gas phase involving hydroxyl cations and hydrogen molecule. The abundance of water molecules in the ISM is governed by the rate at which these reactions occur. Therefore, the measurements of the rate coefficients of these reactions in the interstellar conditions is crucial to the understanding of the formation of water in the ISM and several related processes. In this talk, I will present the results from the first measurements of the rate coefficients of the reactions relevant to the formation of gas-phase water molecules in the ISM.

Predicting the dynamics of an interacting many-body system is often a challenging task either by an analytical method or by numerical simulation. The way to a faster and more accurate solution was embedded in the vision of Feynman’s quantum computers for universal quantum simulations. Ultracold quantum gases offer unique possibilities to simulate quantum dynamics in a highly controllable and precisely tuneable setup. In this talk, I will present an introduction of the field providing a state-of-the-art picture. Specifically, I will present the results obtained with a rubidium Bose-Einstein condensate loaded in an optical lattice. Using a scanning electron microscope [1], we prepared the initial state and observed “Negative differential conductivity” in an interacting quantum gas [2]. Finally, I will present my future research plan. [1] B. Santra and H. Ott, J. Phys. B. 48, 122001 (2015) [2] R. Labouvie, B. Santra, S. Heun, S. Wimberger, H. Ott, Phys. Rev. Lett. 115, 050601 (2015)

Low energy electrons (LEE) can be used as a tool to control chemical reactions at the single molecular level, in gas phase, and in condensed phase. Electron-induced chemical processes at low energies can proceed either via charge transfer followed by electronic excitation of the target, or by the way of dissociative electron attachment (DEA). The DEA process is initiated when the molecule resonantly captures a LEE to form a molecular negative ion (NIR), which is a short-lived electron-molecule compound state. An exciting new aspect of DEA is the possibility of chemical control. The recent discovery of functional group dependence in DEA allows selective bond dissociation (1). Control and selection of chemical reactions using electrons have become more fascinating after it was proposed recently by us that a low energy electron can be used as a catalyst for selective multi-bond breaking reactions (2, 3). This theoretical discovery of formation of neutral molecules by electron catalysed multiple bond breaking mechanism endorse more control over electron induced chemistry. Also, the interest in electron-induced chemistry has recently been renewed by the discovery that low energy electrons play a significant role in damaging and also repairing DNA. Further, there is an increasing realization of its importance in plasma devices and nanolithography. Moreover, electron induced chemistry introduces a new frontier in astro-chemistry. Recent studies identified one hundred eight molecular species in the Interstellar Medium (ISM) through vibrational emission bands (obtained from telescopes such as ALMA) and (sub) millimetre rotational transitions. These species include simplest diatomics (H2 and O2) to complex organic molecules (aldehydes esters, ketones and poly aromatic hydrocarbons). Understanding the mechanism for the formation of such molecules in the ISM opens up the secret of molecular universe. One of the proposed mechanism for the prebiotic synthesis occurs on ice mantles surrounding micron sized dust grains through energetic processors. Recent studies showed that low energy electron can also be an important energy source to initiate this prebiotic synthesis (4). Prebiotic synthesis by low energy electrons can be studied by understanding the chemical reactions through several mechanisms which are active in the low energy regime such as DEA, catalytic electron, excitation and dissociation. Post irradiation interactions inside the ice mantles or inside thick monolayers of films can also shed light on the ISM organic syntheses. For these studies low energy electron collision experiments in condensed phase is one of the ideal situation to stimulate the ISM’s cold (<10K) and empty (>10-12 Torr) environment in laboratory conditions. This talk will focus on astro-chemically relevant LEE induced chemical reactions those we have studied in our laboratories (5, 6) and state of the art design and fabrication of experimental apparatus for LEE-molecule collisions in the condensed phase.

The credentials of Bessel beam with reference to Gaussian, Hermit Gaussian, Laguerre Gaussian are smallest spot size and long-range non-diffraction. Such properties make the Bessel beams indispensable for a variety of applications including fine alignments of the laser beam, optical power transport and atomic guiding. Typically, the Bessel beams are generated by propagating Gaussian beam through axicons. However, the Bessel beams generated though the conventional techniques have the common drawback of fixed range. Additionally, due to the imperfection in the tip of the axicon, the Bessel beams have intensity modulation in the central lobe along the propagation direction. In this talk, I will discuss our new results on a novel experimental technique of Bessel beam generation using hollow Gaussian beam. Since the hollow Gaussian beam has no intensity at the center, it eliminates the effect of the axicon tip and produce a Bessel beam without wiggling in the intensity distribution along beam propagation. Additionally, using higher order hollow Gaussian order, we showed the control in the range of the Bessel beam. We also observe the increase in the peak intensity of Bessel beam using single-pass second harmonic generation (SHG) in lithium tantalate (MgO:sPPCLT) and lithium niobate (MgO:sPPCLN) crystals. I will also cover the basics of Bessel beams and nonlinear optics.

Airy beams, 1D and 2D, are the optical fields with very peculiar properties of non-diffraction, self-healing and self-acceleration. Typically, the optical Airy beams are generated through the Fourier transformation of a cubic phase modulation Gaussian beam. The cubic phase modulation to the Gaussian beam is done using different phase modulators including spatial phase modulator (SLM), cubic phase mask (CPM), non-linear quadratic crystal, and cylindrical lens. However, none of the existing techniques can provide both 1D and 2D Airy beams simultaneously. Here we report on an experimental scheme using a pair of concave and convex cylindrical lenses and some common optical elements available in standard optics lab, producing 1D and 2D Airy beams at same time of high power over a wide wavelength range. The efficiency of our experimental setup for 1D Airy beam generation is more than 80 % and for 2D Airy beam, it is around 70 %, which is much higher than the other techniques, for example, CPM and SLM. We have also studied the frequency doubling characteristics of 1D and 2D Airy beams using a 5-mm-long BIBO crystal. In second harmonic process the power conversion efficiency of 2D Airy beam is higher than 1D Airy beam.

Quantum entanglement, the quintessential curious phenomenon, shows strong non-classical correlations in joint two separate quantum systems, and plays a crucial role in many important applications in quantum information processing, including quantum communication, quantum cryptography and teleportation. Orbital angular momentum (OAM) entanglement in the biphoton eigenmodes has high potential in the field of quantum communication as it can give high dimensional entanglement between the photon pairs. We report a study of biphoton OAM eigenmodes generated in the spontaneous parametric down-conversion process using asymmetric vortex beam. With the help of spiral phase plate (SPP) we generate the symmetric optical vortex beam. The OAM content for different asymmetry is verified using OAM projective measurements. Using the tailored OAM pump beam we have studied the biphoton OAM eigenmodes in the SPDC process, and shown that one can tune or select the desired eigenmodes by simply controlling the asymmetry in the pump beam. Calculation of Schmidt number(K) of the total OAM Hilbert space spanned by the biphoton modes showed that proper tailoring of OAM in the pump beam will increase the dimensionality of the state.

Optical parametric oscillators (OPO) have proved their versatility as a source of coherent radiation over a wide range of wavelengths, which is not possible to achieve with conventional Lasers. For example, the mid-IR wavelength range which is also known as fingerprinting region due to the presence of fundamental absorption bands of various molecules and widely used for high resolution molecular spectroscopy, can not be accessed without the use of nonlinear parametric processes and or OPOs. The OPO sources conventionally produce output radiation in Gaussian intensity distribution. However, generating mid-IR radiation in vortex spatial intensity profile, one can extend the advantages of such sources in terms both spectral and spatial parameters. Using a PPLN based OPO we have transferred optical vortices at near-IR wavelength directly to the mid-IR region and produced high power and higher order optical vortices continuously tunable across 2.3 μm to 3.3 μm. In this talk, I will discuss about the generation technique for optical vortices in mid-IR and their characteristics.

The orbital angular momentum (OAM) states of photons are suitable candidates for the implementation of quantum systems for use in high-dimensional quantum key distribution. Unlike the polarization of light, which offers a two-level Hilbert space, the OAM of photons provides an infinite-dimensional Hilbert space. The effect of atmospheric turbulence on such high-dimensional OAM entanglement will be presented. The evolution of high-dimensional quantum states in an OAM basis shows that the amount of entanglement between two qutrits does not decay fast compared to higher order OAM state. This is in contrast to the situation that was observed for qubits in weak scintillation. Also to implement quantum teleportation, one needs to perform joint Bell measurements using Hong-Ou-Mandel (HOM) interference. Similar to the prior case, turbulence can cause considerable distortion of optical modes traversing atmospheric channels. In this talk, the effect of turbulence on the HOM interference effect will also be discussed. Under certain conditions, turbulence does not have any effect on the quantum interference of OAM entangled state. This opens up the use for quantum communication and quantum synchronization via free-space communication channels.

Graphene has attracted considerable attention due to its massless and gapless energy spectrum. This talk will cover graphene based three different device geometries with experimental evidences of their operation in the THz frequency regime. Dual-gate lateral p-i- n graphene channel transistor (DG-GFET) structure under complementary dual-gate bias and forward drain bias, promotes spontaneous incoherent THz light emission. A laser cavity structure implemented in the active gain area can transform the incoherent light emission to the single-mode lasing. We designed and fabricated a DG-GFET incorporating a distributed feedback (DFB) cavity by using toothbrush-shaped dual-gate metal electrodes. Recently we succeeded in observing broadband (1-7.6 THz range) amplified spontaneous incoherent LED- like emission as well as single mode lasing at the DFB fundamental mode frequency of 5.2 THz at 100K. Asymmetric dual-grating- gate meta-surface structures may promote plasmonic superradiance and/or plasmonic instabilities giving rise to a giant THz gain enhancement at the plasmonic resonant frequencies. Further improvement will be given by a gated double- graphene-layer (G-DGL) nanocapacitor vdW 2D heterostructures. Exploitation of the graphene plasmonics in vdW 2D heterostructures will be the key to realize room-temperature, intense THz lasing.

Solid state laser research has been of interest for decades due to the pace at which new light sources have been identified over the years. The new spectral properties, robustness, compactness, low noise, high–power and reduced costs have all been reasons for the continued interest in the development and deployment of solid-state lasers. In my talk, I will be discussing some of the work that I have done pertaining to the basics of building novel laser sources and also building optical systems for specific applications like ultra-high precision measurement in laser interferometric gravitational wave detectors (LIGO), molecular spectroscopy and trace gas sensing.

Photon is the most popular qubit candidate in quantum information processing. Single photon sources have applications in various quantum cryptographic protocols and they have gained more importance over the years with the discovery of an infinite dimensional OAM (Orbital Angular Momentum) degree of freedom. We study the statistics of a heralded single photon source generated in spontaneous parametric down-conversion by looking at its second order optical coherence. In this talk I will discuss the non-classical nature of the heralded single photon source. I will also discuss the observed variation in non-classicality of the source when it is carrying OAM.

NH and ND molecules play a very crucial role in the prestellar chemistry as they act as intermediate during the formation of the ubiquitous ammonia. Hence there is a need for the accurate modelling of their abundances in space to better understand the physical conditions and the chemical evolution of the prestellar core. We consider H2 and He as the colliding partners as they are dominant species in the interstellar medium and significantly contribute to the excitation of both NH and ND. The earlier studies on the NH-He system were performed using a potential energy surface (PES) which was proved to be relatively close. However, they did not consider the vibration of the NH bond which can impact the magnitude of the collisional data. Hence we take into account the vibration of the N-H molecules.We are also working on the NH-H2 system and preliminary rate coefficients which are first of its kind. These results would be of particular interest because they are first for this system and they should contribute significantly impact the astrophysical modelling by allowing an accurate determination of the NH abundance in the space.

Nanosecondand Femtosecond Laser Induced Breakdown Spectroscopy (LIBS) spectra/data of a series of Nitrates, Pyrazoles and Imidazoles were recorded in air, argon and nitrogen atmospheres to understand the formation of molecular species of CN and C2. Molecular species formation was dominant with fs excitation (versus atomic species dominance in the ns LIBS data).The LIBS spectra were analysed for understanding (a) the influence of molecular structure i.e. type of bonds (C-C, C=C, C-N and C=N) on atomic (C, H, N and O) and molecular (CN, C2 and NH) emissions, (b) effect of surrounding atmosphere on the fs and ns LIBS spectra, (c) correlation between stoichiometric and intensity ratios of molecular as well as atomic species, (d) effect of the number of substituents and their position in the ring on the fragmentation pathways and (e) correlation between oxygen balance and LIBS spectra. Such data will be helpful for discrimination of explosive molecules from non-explosives. Time resolved spectral analysis were performed on molecular (CN, C2) and atomic (C, H, N and O) emissions to understand the plasma dynamics, and alsodetermined the decay times in three atmospheres. Plasma temperature and electron density were measured for Cu I, Li I and Ba I plasma of nitrates with nanosecond (ns) excitation in air atmosphere.IR and Raman spectra of these molecules were also studied both experimentally and theoretically.

Polarization of light is a consequence of the vectorial nature of electromagnetic field and it can be represented as a spin angular momentum of light. Beside that, light beam also carry orbital angular momentum. For most of the analysis, light beam is considered as scalar in nature in which polarization is same all across the beam. But one can couple these two momentum states of light to generate vector vortex beams. Here, we generate such vector vortex beam using optical parametric oscillators (OPO), where we can exploit all the advantages of OPO to generate highly stable, tunable vector vortex beam. Further discussion on generation techniques and application will be presented in the seminar.

Spontaneous parametric down-conversion (SPDC) is a well-known process used to generate twin photons that are correlated in various degrees of freedom. The spatial correlation between the photon pairs guarantees that the angular spectrum of the pump is transferred to the SPDC 'heralded' single photon. Due to the incoherence of individual parametric down-converted photons, the angular spectrum of SPDC does not evidently show the signature of spatial properties of the pump. Here, we theoretically and experimentally show that the amplitude distribution of the pump beam is revealed in the Fourier plane of SPDC distribution restricted by an aperture. Phase measurements show that the SPDC mode distribution does not contain the transverse phase corresponding to that of the pump mode. The results might be useful for applications of SPDC in quantum imaging and quantum information.

The study of ultrafast intense laser interaction with neutral atomic systems revealed ground breaking phenomena such as non-sequential double ionization and high order harmonic generation of attosecond pulses. Because of their different energetics and high degree of electron correlations, anionic systems are expected to present new intense field mechanisms. I will present our recent work on intense field interaction with atomic, molecular and cluster anionic systems. Using the fast beam method and cutting edge 3D coincident fragment imaging, I disentangle all the possible interaction processes. For each fragmentation process, the characteristic angular resolved kinetic energy release distributions are studied as a function of laser peak intensity as well as time resolved in two-color pump-probe experiments. Early studies revealed efficient non-sequential multiple-detachment mechanism that does not rely on re-scattering dynamics, which dominate intense field interactions with neutral species. In particular, I will demonstrate how photodissociation competes with photodetachment, double detachment and Coulomb explosion of the relatively simple F2 ̄ molecular anion. While dissociative photodetachment is dominated by sequential dissociation followed by detachment of the atomic F ̄product, double-detachment exhibits competing sequential and non-sequential contributions, while multiple detachment is non sequential in nature and results in Coulomb explosion.

The talk will be started with the presentation of my Ph.D thesis which is entitled as “A Theoretical Study on the Effect of Temperature on Supercontinuum Generation and Modulational Instability in Liquid-core Photonic Crystal Fiber”. The generation of supercontinuum light and modulational instability in photonic crystal fiber will be explained. The investigation of the effect of temperature on such highly nonlinear phenomena will be detailed. The possibility of using temperature as a control parameter in order to tune the bandwidth of broadband spectrum will be discussed. Following the thesis presentation, a research proposal on the studies on entangled photon pair generation using spontaneous four-wave mixing in erbium doped photonic crystal fiber will be discussed. An useful application of optical fibers is the production of entangled photon pairs using FWM. Various types of fiber have been investigated in the context of FWM assisted entangled photon pairs. In this line, the necessity of investigating erbium doped photonic crystal fiber as a medium to generate entangled photon pairs will be discussed. The methodology and the techniques that are required to carry out the investigation of four-wave mixing in erbium doped photonic crystal fiber in the quantum realm will be explained.

In this seminar, I will review the physical processes leading to ”sub-Doppler” temperatures in laser cooled atom. These processes are generally accepted to be well described by sop called ”Sisyphus cooling”. However, recent experimental and theoretical findings show that the Sisyphus model is at best a partial explanation for the relevant light-atom interaction. Aside from the purely academic question about the nature of the cooling process, there are indications, partially controversial, that the ensuing momentum distribution in the atomic cloud follows a power law. This could in turn makes such samples good candidate for fundamental studies of anomalous diffusion and non-ergodicity. Moreover, the acute sensitivity of the cooling process on the exact atomic structure may also provide a tool for precession spectroscopy.

Hybrid entangled states, having entanglement between different degrees-of-freedom (DoF) of a particle pair, are of great interest for quantum information science and communication protocols. Among different DoFs, the hybrid entangled states encoded with polarization and orbital angular momentum (OAM) allow the generation of qubit-qudit entangled states, macroscopic entanglement with very high quanta of OAM and improvement in angular resolution in remote sensing. Till date, such hybrid entangled states are generated by using a high-fidelity polarization entangled state and subsequent imprinting of chosen amount of OAM using suitable mode converters such as spatial light modulator in complicated experimental schemes. Given that the entangled sources have feeble number of photons, loss of photons during imprinting of OAM using diffractive optical elements limits the use of such hybrid state for practical applications. Here we report, on a simple experimental scheme to generate hybrid entangled state in polarization and OAM through direct transfer of classical non-separable state of the pump beam in parametric down conversion process. As a proof of principle, using local non-separable pump state of OAM mode l=3, we have produced quantum hybrid entangled state with entanglement witness parameter of = 1.25ą0.03 violating by 8 standard deviation. The generic scheme can be used to produce hybrid entangled state between two photons differing by any quantum number through proper choice of non-separable state of the pump beam.

In recent times, vortex dipoles have created a lot of interest in studying in propagation dynamics and optical vortex meteorology. Typically, optical vortex dipoles are created using holographic techniques. But recently we have generated the vortex dipole using an optical parametric oscillator (OPO) while pumping with Gaussian beam in the green, this doubly resonant OPO produces vortex dipole tunable across the wavelength range 968-1181 nm.

The famous uncertainty relation introduced by Heisenberg is a basic feature of quantum theory enshrined in all textbooks. The rigorous form of the Heisenberg-Robertson uncertainty relation expresses a limitation in the possible preparations of the system by giving a lower bound to the product of the variances of two observables in terms of their commutator. However, it does not capture the concept of incompatible observables because it can be trivial, i.e., the lower bound can be null even for two incompatible observables. Here, we will prove two stronger uncertainty relations, relating to the sum of variances, whose lower bound is guaranteed to be nontrivial whenever the two observables are incompatible on the state of the system. These "stronger uncertainty relations" go beyond the Heisenberg-Robertson relation and suggest that quantum mechanical uncertainties respect more stringent bounds than what is thought before.

Motivated by a recent observation of unusually large differences between the measurement and theoretical studies on the field shift ratio of the D_2 and D_1 lines in the Ca^+ ion, we investigate the role of the nuclear charge distribution in the determination of the field shifts. In my talk, I shall discuss about the theoretical results of the field shift constants obtained from both the uniform and Fermi nuclear charge distributions. To validate the results, calculations are carried out using two distinct procedures as finite gradient approach and evaluation of the expectation value in the perturbative framework. At the end, I shall also highlight possible scopes to remove discrepancies between the experimental and theoretical results further.

A novel scheme for coherent generation, control and manipulation of structured beams in a system of homogeneously broadened atomic vapor with atoms in a closed three-level Λ-configuration has been used to explain the recent experimental results of Radwell et al. Phys. Rev. Lett. 114, 123603(2015). The key feature underlying structured beam generation is transverse magnetic field induced phase dependent absorption between two Laguerre-Gaussian beams which connects two optical transitions of opposite polarities. We show how the coherent control field can be used to manipulate an azimuthal modulation of the absorption profile that is dictated by the phase and polarization structure of the probe beam. The mechanism of efficient generation and manipulation of an optical beam may have important applications in information science and optical communications.

Ultrafast laser direct writing is a technique with no parallel to deposit energy locally in short time scales to alter properties of materials (such as electrical, optical, and mechanical) without any damage to surroundings. The unique nonlinear interaction of light with matter due to high intensities associated with short pulses (of the order of femto-seconds) confines the modification within the focal volume of ultrafast light. Clear plastics (polymers) that are transparent exhibited fluorescence and para-magnetism upon interaction with a femtosecond laser. Bits of information can be encoded and stored in polymers by modifying locally with a femtosecond laser. 32 grey levels (5-bit) of information have been stored in a polymer Poly Methyl Methacrylate (PMMA) without any loss of information throughout the volume with a storage capacity up to 0.2 TB/disc. There have been attempts to overcome diffraction limited structures with standard ultrafast laser writing technique. Sphere assisted lithography (photonic nanojets) was shown to be promising to obtain not only diffraction limited structures but also micro-structuring over large surface areas with the help of mono-layers of spheres. Micro-structuring on a large surface area was demonstrated on different substrates including silicon, glass and quartz with dielectric spheres such as polystyrene and silica. Sphere assisted lithography/Photonic nanojet lithography technique was integrated with Laser Induced Forward Transfer (LIFT) technique to deposit 2D array of metal nanodots, and nano-triangles. By controlling the laser energy, metallic structures of different size, and shape were obtained. Ultrafast laser writing and photonic nanojets are promising for future applications in the areas of integrated photonics.

Internet data traffic is increasing exponentially with time and putting pressure on optical telecommunication networks whose backbone mainly consists of single mode fibers. To increase the data carrying capacity of single mode fibers, different multiplexing schemes as well as data formats have been proposed and demonstrated experimentally. These multiplexing schemes based on the properties of light which include wavelength, phase, amplitude and polarization. But these schemes are not enough for future capacity crunch, therefore, new multiplexing technique must be explored. To overcome this upcoming issue in communication systems, Orbital Angular Momentum (OAM) mode multiplexing has been proposed recently. OAM is an intrinsic property of light, which is quantized and allows infinite states of light unlike polarization. In this talk, I will discuss about OAM of light, design criteria for OAM supported fiber and data transmission study through it.

The effect of an additional transverse magnetic field (TMF) is studied on Hanle resonances for both linearly (&#963;) and elliptical polarized light in atomic Rubidium. The TMF redistributes the population among the Zeeman sublevels and its effect is found to be opposite for longitudinal and transverse magnetic field scans for elliptical polarized light. A new technique for measuring magnetic field using Hanle resonances with &#960;-polarized light is reported with pure Rb vapor cells and a cell buffer gas. It is shown that with a &#960;-polarized, no resonance signal is observed in absence of the TMF. When the TMF is applied, two dips are observed on either of zero scanning magnetic fields in the transmission spectrum. The separation between the two dips is linearly proportional to magnitude of the TMF, which can be used for magnetometry. The influence of a closed transition on neighboring open transitions that are partially resolved under Doppler broadening is also studied. We show that a sign reversal from an electromagnetically induced transparency (EIT) resonance to an electromagnetically induced absorption (EIA) resonance occurs with increase in ellipticity for the Fg = 2 &#61664; Fe = 1 and Fg = 2 &#61664; Fe = 2 transitions of 87Rb D2 line in a transverse field scan.

In astronomy and astrophysics, there exist two several-decade-old mysterious spectra. One is referred to as the diffuse interstellar bands (DIBs) -- the absorption features that are observed in the visible to the near-infrared spectra of astronomical objects. The other is termed as the unidentified infrared emission bands (UIEs) -- the emission features observed in the mid-infrared spectra of the astronomical objects. Despite the observation of several hundred lines in the DIBs over nearly a century and several bands in the UIEs over four decades, only very few of them could be conclusively attributed to any known chemical species. At the Max Planck Institute for Nuclear Physics in Heidelberg, we are developing a novel spectroscopy technique with the objective to solving these mysterious spectra. In this technique, the molecular ions proposed to be the candidates for the spectral features in the DIBs and the UIEs (big carbon clusters such as fullerenes and polycyclic aromatic hydrocarbons) are stored in a cryogenic, electrostatic ion beam trap that simulates the true interstellar environment (with the temperature of 10 K and residual gas density of about 2000 particles/cm3). The stored molecular ions are then subjected to excitation by the laser light spanning the range (typically visible to near-infrared) of the absorption features of the molecular ion under concern. At resonance, the absorbed energy will be re-distributed among the vibrational modes of the molecule followed by the delayed emission of mid-infrared radiation from the triplet states. A fraction of the emitted light will be guided onto highly sensitive blocked impurity band (BIB) detectors which feature extremely low dark current and high sensitivity. Scanning the excitation laser wavelength provides the absorption spectrum (for the DIBs) and scanning the emitted infrared wavelength provides an emission spectrum (for the UIEs). The measurement scheme, preparatory work toward its implementation, and the current status of the experimental setup will be presented.

It is well known that classically a particle can not accelerate in absence of an applied force. Surprisingly, in 1979, Berry and Balazs found that the free particle Schrodinger equation admits a wave packet solution that linearly accelerates and is non-dispersive. Several different explanations have been offered to understand unusual behavior of such wave packets, which provide valuable insights into working of quantum mechanics. In this talk, we shall review some of these explanations, and shall discuss some of our recent work in this area.

The developments in the field of Quantum Information science require successful candidates for quantum bits (qubits). Quantum states of a single photon are ideal qubit candidates. Spontaneous Parametric Down-Conversion (SPDC) is an important non-linear process in which heralded single photons are generated. Photons can exhibit different probability distributions based on the nature of the source. Classical sources like thermal/partially coherent light show super-Poissonian statistics and coherent light show Poissonian statistics, while single photon sources are characterized by the non-classical sub-Poissonian statistics. In this talk, I will discuss about the statistics of both classical and non-classical sources of light on the basis of photon number fluctuations. Also, I will discuss the sub-Poissonian statistics of Type-I SPDC photons and hence the confirmation of their non-classical nature.

Half a century back, Dicke studied a model of a collection of two level atoms interacting with a single cavity mode. It was found that when the atoms are in what is called Dicke state, the photon emission probability is significantly larger than the spontaneous emission probability, which was called super-radiance. In this talk, it will be shown that such a super-radiant state of photons is actually a coherent state. The relation between Bose-Einstein condensation, spontaneous symmetry breaking and super-radiance in photonic systems will be shown. It will be shown that super-radiant emission of photons from Dicke states is fundamentally different from spontaneous and stimulated emission phenomena.

In this talk I will discuss some of the advances in using light especially lasers for imaging biological samples in three dimensions and manipulating them. The gold standard in high-resolution imaging is confocal microscopy that primarily uses linear fluorescence. Non-Linear optics has also found its way into exploring the biological world. Tools like multiphoton fluorescence and Second Harmonic Generation (SHG) are being increasingly used to image biological samples and extract finer details. Newer approaches are also using light sheets for faster and deeper imaging of whole organisms and thick tissues. Precise focusing and nonlinear confinement of NIR ultrafast laser light is being used for precise nano-surgical interventions.

Orbital angular momentum (OAM) of light beams has been recently explored for the implementation of many quantum information tasks. This is an infinite dimensional degree of freedom which can be used along with polarization. However, for many protocols we just need to have two dimensional qubits of OAM. Experimentally this was done by restricting the detection to two OAM states, which causes huge loss of photons. Instead, we address the possibility of using even/odd states of OAM of photons for the quantum information tasks so that the photon number will be preserved. We consider single photon qubit states as well as two photon entangled states in even/odd basis of OAM. We present a method for the tomography and general projective measurement in even/odd basis. With the general projective measurement, we can have the Bell violation which can be used in quantum cryptography. I will describe schemes for the various measurements and implementation of quantum protocols such as super dense coding and teleportation.

Surface plasmons are free charge oscillations occur at the interface of metal and dielectric layer. Surface plasmon resonance (SPR) based phase measurement technique provides higher accuracy than conventional intensity measurement techniques. In this talk I will discuss some of our recent results on SPR based radially sheared interference imaging and novel scheme of incoherent and coherent Moiré pattern generation and their possible applications in switching, logic operations and non-contact testing of surface profilometry.

Recent developments in the field of structured beams have led to a new class of optical beams known as 'perfect' vortices. Unlike normal optical vortices, the perfect vortices have ring radius independent of its topological charge (order). Such property makes perfect vortices interesting for many fields in science and technology. In this talk I will discuss on our recent work on nonlinear generation of "perfect" vortices. Based on Fourier transformation of the higher order Bessel-Gauss beam generated through the combination of spiral phase plate and axicon we have transformed the Gaussian beam into perfect vortices of power 4.4 W and order up to 6. Using single-pass second harmonic generation (SHG) of such vortices we have generated perfect vortices at green wavelength (530 nm) with output power of 1.2 W and vortex order up to 12 at single-pass conversion efficiency of 27%, independent of the orders. This is the highest single pass SHG efficiency of any optical beams other than Gaussian beams.

Corroborating the analogy between non-Hermitian quantum system and counterpart optical geometries with suitable amount of simultaneous gain and loss, I plan to discuss an innovative scheme for asymmetric mode conversion in a coupled optical system under certain condition in the strong coupling regime (beyond the PT symmetry limit) exploiting singularities (in eigen values and eigen vectors) associated with avoided crossings (in the regime where adiabatic evolution fails) as an efficient tool. Novel propagation dynamics of light wave through this special optical structure is evident, which is being explored in the context of optical isolation for integrated/ on-chip photonics applications. From fundamental physics point of view and applications in photonics like realizing compact random lasing in one dimensional disordered system (longitudinal direction mapped onto time), I plan to focus on my latest findings to demonstrate that the simultaneous presence of spatial and refractive index disorder favors Anderson localization of light. This study has revealed several underlying interesting features of light confinement to a localized state in such a medium of finite length and showed that beyond the point of localization, light indeed propagates without any diffractive spread in the transverse direction in a disordered lattice, a feature that mimics waveguide-like propagation. The hallmark stochastic nature of the phenomena has been encountered in both simulations and experiments using ultrafast laser inscription (ULI) technique.

Stable clusters and molecules under effect of external perturbation attain excited states. This excited system relaxes via various mechanisms at different timescales after perturbation. By studying the time evolution of such excited systems, different types of relaxation mechanisms involved in the de-excitation process can be probed as a function of time, thus, yielding vital information about the underlying dynamics involved. In this talk, I will present the experimental studies that we have performed to understand the time evolution of excited cluster anions and also briefly discuss about the methodology to study the time evolution of excited molecules.

When a high power laser pulse from a multi-terawatt (1012 Watt) laser system is focused on a solid surface, a special type of plasma is formed on the solid surface, a high temperature and high density plasma with very steep density gradient. The state of the matter which is created here is comparable to the inner material of a stellar object. Information about these high intensity femtosecond laser plasma interactions is required in inertial fusion research, laboratory astrophysics and many other purposes. High intensity short pulse laser plasma interaction also produces highly energetic short bunches of charged particles (electrons, protons and ions). Next generation of particle accelerators are predicted to be based on laser plasma interaction. They also produce high energetic electromagnetic pulses such as high-order harmonics, soft and hard x-rays. Recently we found high intensity laser plasma interaction also generates GHz and THz pulses with high energy per pulse. Intense broadband THz pulses are opening new scientific areas to explore, such as nonlinear optics in the THz domain, as well as single-shot THz spectroscopy and imaging. Intense THz pulses can also be used to develop THz streak cameras, which could measure the temporal characteristics of femtosecond X-ray and electron bunches generated by methods such as high-intensity femtosecond laser-plasma interaction. This technique of THz pulse generation can be a potential source of ultra-broadband and intense THz light pulses. Particle-in-cell (PIC) simulations have predicted that GV/cm THz fields can be generated by such laser-plasma interactions. An attractive advantage of this method is that unlike other conventional THz sources (such as the optical rectification technique), there are no known limits in the maximum laser intensity that could be used to drive these laser-plasma THz sources. Therefore, these methods could potentially be driven at very high laser intensities, giving rise to even higher THz yield. In this presentation I’ll mainly focus on a part of my postdoctoral research which is intense THz pulse generation via high intensity femtosecond laser plasma interaction which I have developed at INRS-EMT. Generated THz pulses are characterized and then pulse energy is optimized by controlling plasma conditions and interaction process. These THz pulses can be used as novel probe for laser plasma interaction process. Our recent research covering this prospect will also be discussed.

Predicting the dynamics of an interacting many-body system is often a challenging task either by an analytical method or by numerical simulation. The way to a faster and more accurate solution was embedded in the vision of Feynman?s quantum computers for universal quantum simulations. Ultracold quantum gases offer unique possibilities to simulate quantum dynamics in a highly controllable and precisely tunable setup. In this talk I will present two examples where we have investigated the quantum dynamics of a Bose-Einstein condensate loaded in a 1D optical lattice. In the first experiment we observe Negative differential conductivity, which is a widely exploited mechanism in many areas of research dealing with particle and energy transport. In the second experiment we investigate the non-equilibrium steady-states (NESS) of a driven-dissipative superfluid. NESS constitute fix points of the phase space dynamics of classical and quantum systems. They emerge under the presence of a driving force and lie at the heart of transport phenomena such as heat conduction or current flow.

Understanding the coherent interaction between light and matter is important in many aspects of quantum information sciences. We have embarked on a study of coherent interaction of light fields with cold ensemble of ^{87}Rb atoms under electromagnetically induced transparency condition. We will talk about our results on the noise correlation spectroscopy for two laser fields interacting with cold ^{87}Rb atoms. On keeping one beam at atomic resonance and scanning the detuning of the other around the resonance, a symmetric correlation spectrum with correlation and anti-correlation features at different two-photon detunings is observed. In an another study of noise correlation spectroscopy for a resonant fixed beam, we found that the correlation spectra depend on "which way the detuning of other beam is being scanned". A beautiful Physics dealing with the effect of light induced forces in cold atoms explains our seemingly counter-intuitive results in the correlation spectra.

Optical tweezers is a very versatile tool. In this talk, this tool has been used to address a couple of questions in biology. First, we ask how does the kinesin motor 'walk' on a microtubule? In order to answer this question, a birefringent liquid crystal microparticle was attached to the kinesin and the rotation of the particle studied as the kinesin moves on the microtubule. It was observed, quite in contrast to the expected 'asymmetric mechanism', that it actually exhibits the symmetric one while simply turning in one sense during motility. We also show that the kinesin can be twisted by 45 degrees without damage to the molecule and released to observe relaxation. In the second part of the talk, a new technique of determining asymmetry of arbitrary objects trapped in tweezers relying upon the cross correlation of the rotational Brownian motion and translational Brownian motion is demonstrated. This technique is applied to hypotonic RBC's to show the degree of anisotropy.

Recent development in the field of structured beams have resulted in a special class of optical vortices, known as perfect vortices (PVs), where the radius of the vortex ring is independent of its order. Conventionally, the PVs are generated through the Fourier transformation of Bessel-Gauss (BG) beam. As a result, variation in the size of such vortices requires complicated imaging systems. Howeve, we have devised a simple experimental scheme to generate and vary the size of the PVs using a convex lens and an axicon. In this talk I will discuss on our recent results on generation of variable size perfect vortex beam of different orders and their effect in the angular spectrum of spontaneous parametric down-converted photon.

High-power, ultrafast ultraviolet (UV) radiation at high repetition rate is of great interest because of its variety of applications in many fields of science and technology. In this talk I will discuss on our recent work on development of such a UV source. Using nonlinear wavelength conversion techniques on an Ultrafast ytterbium fiber based Laser, we have generated ultrafast UV radiation at 355 nm with an output power as high as 1.06 W.

Au-TiO2 nanoparticles are expected to have better nonlinear optical properties for its applications in optical switching, optical limiting and other optical devices. We synthesize Au-TiO2 nanoparticles by sol-gel process and deposit on silicon substrates to form nanocrytalline Au-TiO2 thin films using spin coating method. These thin films are analysed using different characterization techniques such as X-ray diffraction, UV-visible absorption etc. Next, we measure the nonlinear refractive index and nonlinear absorption coefficient of these metal doped TiO2 nanocrystalline films using the z-scan technique. In this talk, I will be explaining the synthesis of these nanocrystalline thin films, its characterization techniques and present the results obtained.

The interpretation of the quantum state function \psi has been of considerable debate since its inception. The most important issue is whether \psi; is an ontic and complete description of physical reality, or is it an epistemic and incomplete state of knowledge about an underlying reality? The Copenhagen school advocated the former interpretation whereas Einstein favoured the latter interpretation. Recently, N. Harrigan and R. W. Spekkens [Found. Phys. vol. 40, pp. 125-57 (2010)] introduced a mathematical framework which has brought about clarity in discussions on ontic versus epistemic interpretations. Surprisingly, several theorems have since been proven within their framework [e.g. M. F. Pusey, J. Barrett, and T. Rudolph, Nature Phys. vol. 8, pp. 475-78 (2012)] which show that \psi-epistemic models are incompatible with standard quantum mechanics. There is a simple argument using time evolution to show that maximally \psi-epistemic models cease to be so with time. It will be argued that an Einstein type epistemic interpretation is still possible by embedding quantum mechanics in a larger Hilbert space of ontic states so that quantum states are a subset of these states, and hence epistemic in character.

Polycyclic Aromatic Hydrocarbons (PAH), are known to be the carrier of several infrared features in the Interstellar Medium (ISM). However, the synthesis of smaller and large PAH molecules were to-date not well understood at astrochemical conditions. However, benzene synthesis from propargyl alcohol in fact had opened the possibility of an entirely new reaction network, the ?propargyl channel to PAH?, on the icy mantles of cold dust grains. From the complex chemical network that prevails in the ISM we could expect a variety of propargyl containing molecules that are present and awaiting discovery. Therefore, it is imperative to understand the physico-chemical properties of propargyl compounds at astrochemical conditions. Here, I will be presenting the first results of propargyl containing compounds such as propargyl ether and propargyl alcohol.

Vector beams are the solutions of vector wave equation and having spatially varying polarization throughout the cross section. These are doughnut shaped beams like scalar vortex beams and ring shaped beams, with phase and polarization being undefined at their center. Such vector vortex beams are classified into four types depending upon the spatial variation in their polarization vector. Recent investigation identifies that vector beams are classically entangled in polarization and orbital angular momentum (OAM) and it can violate Bell?s like inequality. Moreover, demonstration shows that classical entanglement can also be used for teleportation protocols. The generation of all these four types of vector beams using modified polarization Sagnac-interferometer with a vortex lens will be discussed along with the non-coaxial superposition of two vector vortex beams.

Carbon dioxide being one of the most abundant molecules in the InterStellar Medium (ISM) had got the attention of spectroscopist to understand the morphology as it condenses to form ices in the ISM. Laboratory experiments simulating ISM dry ice were performed intensively since the 1980's in all aspects from morphology, reactivity and desorption, where almost all of these studies depended on the infrared (IR) spectroscopy, which eventually had lead to the finding of dry ice in various sources studied by the Spitzer space telescope. However, still there are fresh debates on the morphology of dry ice as it condenses from the gas phase. In this talk, I will review the morphology of dry ice probed using IR spectroscopy and then discuss how our fresh results at VUV wavelengths help understand it better.

Low energy free-electrons can be used as a tool to initiate control and manipulate chemical reactions and nanoscale molecular synthesis. The overall sequence that leads to the final products involves resonance capture of low-energy free-electron by a reactant molecule and subsequent formation of an intermediate electron-molecule compound state. Our theoretical studies have made a remarkable proposition that the low-energy free-electron can also act as a catalyst in a chemical reaction. Catalytic activity of the electron is bound to the metastability of the electron-molecule compound state. Followed by this theoretical proposition of catalytic electron, many of the reaction mechanisms including the enzymatic repair of thymine dimer, a photo-damaged molecule, and various reaction steps in electrochemical processes have been attributed to the catalytic activity of the electron. We have also experimentally verified that electron is a catalyst by observing the production of CO2 in a resonant, free-electron capture by formic acid. Our low-energy free electron impact experiment sophisticated with in-situ molecular probing using Fourier transform infra-red (FTIR) spectroscopy shows that the resonant formation of CO2 at 6 eV and 11 eV of incident electron is indeed catalysed by the free-electron. This talk covers the details of theoretical discovery of catalytic electron and its experimental verification using electron impact studies in condensed phase.

Sulphur bearing molecules play their part in the complex chemical network that prevails in the icy bodies of the Solar System and on the cold dust grains of the interstellar medium. With the recent discovery of ethanethiol in the interstellar medium and repeated discovery of carbon disulphide in comets it is imperative to understand these molecules at low temperatures in order to reveal the role played in chemical reactions. In this talk, I will be presenting the first results on sulphur bearing molecules, such as ethanethiol and ammonium dithiocarbamate, in low temperature molecular ices obtained from the new 10 K experimental facility.

We generate classical Bell like states of polarization and orbital angular momentum (OAM) using a laser beam. These are equivalent to the hybrid entangled systems in which two degrees of freedom of a single particle are entangled. We consider a cyclic evolution of the polarization state which introduces a relative phase to the generated Bell state. We observe that the violation of Bellâ??s inequality depends on the relative phase and the choice of our measurement basis. We also show that the non-separability remains preserved under scattering through a random medium like rotating ground glass. We verify this by measuring the degree of polarization and observing the intensity distribution of the beam when projected to different polarization states, before as well as after the scattering.

Quantum entanglement is the genuine quantum property of a composite system that forbids individual parties to be attributed with distinct quantum states even if they are far apart from each other. Entanglement has been identified to be an important resource for performing quantum tasks, such as quantum communication and quantum computation. Generation of entanglement in composite systems requires interaction between its subsystems, and hence strongly interacting systems, e.g., quantum spin chains, form physical resources of entanglement. A quantum information perspective on many-body systems generates new ideas and leads to development of novel methods for solving many-body systems. Several concepts developed in quantum information science turn out to be useful tools for detecting co-operative phenomena, like quantum phase transitions. In this talk, I will briefly introduce few key concepts that steer cross-fertilization between these two traditional disciplines of research, and present some of our recent works in this direction. Specifically, I will talk about characterization of quantum correlations in quantum spin systems with defects, and dynamical evolution of entanglement followed by a sudden quench.

This seminar will highlight the multi-disciplinary groundwork for the pioneering in situ organic compositional analyses of nuclei surface of comet 67P/Churyumov-Gerasimenko performed by the Cometary Sampling and Composition Experiment (COSAC) in November 2014. COSAC is a Gas Chromatograph-Mass Spectrometer on board the Philae Lander probe of European Space Agency?s Rosetta mission to comet 67P/Churyumov-Gerasimenko.The talk introduces three holistic yet myriad experimental and analytical campaigns, 1) carried out at a synchrotron radiation facility (DESIRS Beamline ? Synchrotron SOLEIL),2) with the COSAC flight spare model (located at the Max Planck Institute for Solar System Research), 3) with the tentative comet surface analogue material ?tholin?(synthesized at NASA Ames Research Center), all directing to the objectives of COSAC subsequent to its landing on 67P.

The detection of emission bands at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 um towards many astronomical objects in the interstellar medium (ISM) has opened up new prospects in observational, laboratory and theoretical molecular astrophysics.These features have been proposed to be emitted by transiently heated large (50 to 100 C-atom) Polycyclic Aromatic Hydrocarbon (PAH) molecules, although no individual PAH has been identified in the ISM yet. In this talk I will be discussing the emission mechanism and the spectroscopy involved. I will also be discussing the mid-IR spectra of interstellar PAHs and its variation based on theoretical spectroscopic studies. The talk will try to cover substituted PAHs as carriers of some of the observed bands.

Electronic dynamics of the stable states are rather less-complex and have been quite successfully studied for many small as well as large molecular systems. On the other hand, nature of highly excited states which are often unstable is hard to investigate, thus not known comprehensively. Dynamics of large systems having many degrees of freedom is normally resulted in the intermixed kinematics, and consequently extremely hard to untangle. This restricts one to consider a systematic approach: to start from simple and small systems. By using excitations from many ionization schemes and comparing the dissociation processes in near-identical molecular systems, we have analyzed these states in order to probe their properties. I will discuss some of the results obtained from the analysis of dissociation dynamics of two diatomic molecules N2 and CO in electron- and photon-impact processes. Based of the study, few common features of their highly unstable electronic states that can be materialized will be presented.

Interferences in coherent emission of photoelectrons from two equivalent atomic centers in a molecule are the microscopic analogous of the celebrated Young's double-slit experiment. By considering inner-valence shell ionization in the series of simple hydrocarbons C2H2, C2H4 and C2H6, we show that double-slit interference is widespread, and has built-in quantitative information on geometry, orbital composition and many-body effects. A theoretical and experimental study is presented over the photon energy range 70-700 eV. A strong dependence of the oscillation period upon the C-C distance is observed, which can be used to determine bond lengths between selected pairs of equivalent atoms with at least 0.01 Å accuracy. Furthermore, we show that the observed oscillations are directly informative of the nature and atomic composition of the inner-valence molecular orbitals, and observed ratios are quantitative measure of elusive many-body effects. The technique and analysis can be immediately extended to a large class of compounds.