TUnable Liquid crystal Polarimeter (TULIP) for MAST
A
Tunable Liquid Crystal Polarimeter (TULIP) for the upcoming MAST telescope is
proposed. The design is based on tunable retarders called Liquid Crystal
Variable Retarders. In the first phase instrument is designed for operation in
the wavelength range (600 to 900 nm). The specifications are decided with the
goal of achieving polarimetric sensitivity of 1e-3 within few seconds. For
higher sensitivity one can make long integrations, which is possible with
adaptive-optics. The polarization analysis of the modulated beams can be done in
single beam mode (large FOV, less sensitivity) as well as dual beam mode
(reduced FOV, more sensitive). This first mode is suitable for good seeing and
operational AO system. The second mode of dual beam is useful
when seeing is poor and AO is not operational. The FOV constraint is due to
single CCD camera in proposed MAST filtergraph (Imager for Mast) and
spectrograph (RES). However, by using two identical CCD cameras we can do
sensitive polarimetry over a large FOV. The sensitivity in case of dual beam is
larger as all the photons are utilized as compared to single beam mode where
only 50% are used. As the accuracy of polarimeter is determined by quality of
calibration, a dedicated unit with good quality calibration optics is proposed
for routine calibration.