Aluminization Plant

Telescope mirrors are coated with a thin metallic film to improve photon collection. However, this coating degrades over time due to environmental factors, requiring periodic recoating to maintain the telescope's performance. During the recoating process, the mirrors are removed from the telescope and transported to the coating facility. The process involves three stages: removing the degraded coating, cleaning and drying the optical surface, and applying a new coating inside a coating chamber. The telescope remains out of operation throughout the recoating activity.

At the PRL Mount Abu Observatory, two coating plants have been installed: one for the PRL 1.2m telescope mirrors and another for the PRL 2.5m telescope mirrors. The telescope mirror coatings typically have a thickness of 1500 angstroms with a uniformity better than 5%.


1.2m Mirror coating plant

In 2002, a dedicated thermal evaporation-based mirror coating plant was developed and installed for the PRL 1.2m telescope. This plant is currently used to apply bare aluminum coatings to the primary and secondary mirrors of the 1.2m telescope. During the coating process, the mirror is positioned vertically, with its optical axis horizontal, inside the chamber. The plant can accommodate substrates up to 1.2m in diameter for thin-film coating. For the removal of degraded aluminum coatings, cleaning, and drying of the mirror's optical surface, a separate coating removal and mirror cleaning station is utilized.

2.5m Mirror coating Plant

Since the 1.2m coating plant cannot accommodate the mirrors of the 2.5m telescope due to size constraints, a dedicated plant was developed and commissioned in 2023 for the PRL 2.5m telescope mirrors. The primary and secondary mirrors of the 2.5m telescope were successfully re-coated for the first time in the last quarter of 2023 using this new plant. This plant employs a thermal evaporation technique for applying thin-film bare aluminum coatings. During the coating process, the mirror is positioned horizontally, with its optical axis vertical, inside the chamber. The plant can handle substrates up to 2.5m in diameter for re-coating. The entire coating sequence is automated with specialized software developed for the plant. Additionally, a dedicated coating removal and mirror cleaning station was developed for removing degraded aluminum coatings, cleaning, and drying the mirror's optical surface.