Abstract:
The reflectivity of the optical components of the 0.7-m GROWTH India Telescope (GIT) at
the Indian Astronomical Observatory (IAO), Hanle, was measured using a CT7 reflectometer
at seven discrete wavelengths ranging from 365 to 970 nm. The measurements were carried out
to assess the present condition of the reflective coatings and establish baseline data for future
monitoring.
The primary mirror was measured at four accessible positions and showed an average reflectivity
of approximately 78%, with a scattering loss of around 18.2%. The reflectivity varied
with wavelength, ranging from 72.7% at 464 nm to 82.4% at 624 nm. Measurements of the
secondary mirror at two positions yielded an average reflectivity of approximately 90.2%, with
a scattering loss of about 2%.
The results indicate comparatively higher dust accumulation and lower reflectivity for the
primary mirror. The measurements provide baseline data for future assessment of coating
degradation and optical performance through periodic monitoring under the environmental
conditions of the Hanle site.
