CTIO 0.9m (36") telescope reflectometry data

JUNE 99: We aluminized both mirrors. Last time was: 6June97 for M1 and 9Dic97 for M2. See the following plots. In the text below, we give the average number (2 points sampled each time) at 550nm for a rapid evaluation of, respectively, the reflectivity and the scattered light.

• M1: was very dirty visually, covered with dust (77.0% and 10.80%). We noted the presence of lots of particles longer than 0.5mm, even a few (10) >1mm. First we cleaned it with CO2 (86.7% and 4.40%). Then we washed it with Orvus soap (contact with natural sponge), rinsed with bi-distilled water and dried with dry nitrogen (91.0% and 1.10%). The result was spectacular, close to a fresh aluminium!

• M2: was quite clean after removal from the telescope (88.1% and 1.80%). Cleaning it with C02 made it slightly worse! (87.9% and 1.90%). Aluminizing improved a lot the reflectivity but not the scatter (89.8% and 1.80%).

M2 reflectivity and M2 scattering

LATEST:12 April 00: We washed M1. The following graph show reflectivity and scatter as we found the mirror after 10 months (without cleaning it at all), after a CO2 cleaning, and finally after washing. Last aluminizing data is also plotted for reference. Final state of the mirror is actually better than after aluminizing (!), a curious phenomenon also noticed by Giordano at the NTT using Collodion peeling films!

The curious effect of increasing scatter between 400and 700nm as found after 10 months (yellow line) is not explained. Same phenomenon was measured 10 months ago, just before aluminizing...

Between June 97 and June 99, M1 reflectivity as decreased by 0.33%/month (400nm) and 0.18%/month (700nm) and scatter has increased by 0.32%/month (400nm) and 0.44%/month (700nm). Between June 99 and April 00, M1 reflectivity as decreased by 0.30%/month (400nm) and 0.17%/month (700nm) and scatter has increased by 0.36%/month (400nm) and 0.52%/month (700nm).