1.5m telescope reflectometry data
A/ PRIMARY MIRROR:
3 APRIL 01: Reflectometry and BRDF data with Iris:
This corresponds to a 1.1% reflectivity loss per month at 530nm (average over 5 months), about twice higher than usual.
SEPTEMBER and NOVEMBER 00: regular washing in September improved reflectivity by 8.5% in average. Reflectometry and BRDF data with Iris (before/after wash respectively):
These numbers are actually close (some are even slightly higher!) than what is quoted in the litterature for a new coating. In October, rain leaked through the dome shutter and contaminated M1 (lots of long ugly white stripes across the mirror): in the bad areas (about 20% of the mirror), about 6% loss was measured but it was well recovered with washing in November (only about 1.8% less compared to previous wash). The reflectivity and BRDF improved to:
MARCH 00: mirror washed on the 21st, see the plots of reflectivity and scattering (the numbers after the last aluminizing are also plotted for reference). All data with the Minolta.
SEPTEMBER 98 - MARCH 00: regular CO2 cleaning
See the plots of reflectivity and scattering for that period (data with the Minolta).
Reflectivity decreases in average by 2.5% per year and scatter increases by 2.0% per year. There seems to be a seasonal trend as the slopes are much higher in 'summer' (October to April) when the site humidity is higher (32-55%), which makes the dust stick more easily onto the glass: summer slope for R and SC is about 0.63% per month, whereas it is only about 0.05% per month in 'winter' (May to September, RH is 12-32%).
Numerical data: in parenthesis (last column) is the number of points sampled on the mirror for each result. Each point on the mirror is sampled 3 times (averaged by the reflectometer). On some dates (like 10Jan98), we also indicate the variations (+/-) in the data. For the first row, replace "before/after CO2 cleaning" by "before/after Al". The case "before Al" means the mirror was CO2 dusted and measured just before realuminizing.
|
DATE |
% Reflectivity before CO2 cleaning |
% Reflectivity after CO2 cleaning |
% Scattering before CO2 cleaning |
% Scattering after CO2 cleaning |
Elapsed time (weeks) between new Al and CO2 |
||||
|
|
400nm |
700nm |
400nm |
700nm |
400nm |
700nm |
400nm |
700nm |
|
|
2-Sep-98 +/- |
87.42 0.47 |
84.22 0.13 |
93.46 0.74 |
89.11 0.50 |
4.49 0.71 |
4.40 0.39 |
1.47 1.41 |
0.77 0.71 |
new aluminium (3) |
|
10-Sep-98 |
95.16 |
90.1 |
94.53 |
89.75 |
0.61 |
0.43 |
0.49 |
0.35 |
1 (1) |
|
14-Oct-98 |
94.1 |
88.89 |
95.23 |
90.05 |
1.06 |
0.80 |
0.63 |
0.54 |
6 (2) |
|
13-Nov-98 |
no data |
|
|
|
|
|
|
|
10 (0) |
|
11-Dec-98 |
91.59 |
87.23 |
93.58 |
89.08 |
1.95 |
1.61 |
1.51 |
1.18 |
14 (4) |
|
10-Jan-99 +/- |
91.62 1.78 |
86.91 0.83 |
93.69 0.9 |
88.76 0.78 |
1.77 0.01 |
1.98 0.04 |
1.41 0.16 |
1.32 0.22 |
18 (4) |
|
19-Fev-99 |
91.18 |
86.46 |
92.24 |
87.58 |
3.34 |
3.34 |
3.12 |
2.55 |
23 (3) |
|
19-Mar-99 |
92.34 |
87.46 |
92.59 |
88.06 |
2.61 |
2.56 |
2.69 |
2.11 |
27 (3) |
|
17-Apr-99 |
92.27 |
87.55 |
92.63 |
87.93 |
2.94 |
2.45 |
2.91 |
2.24 |
31 (3) |
|
16-May-99 |
92.18 |
87.64 |
92.43 |
87.89 |
2.75 |
2.38 |
2.69 |
2.18 |
35 (3) |
|
13-Jun-99 |
92.58 |
87.87 |
92.75 |
88.12 |
2.54 |
2.25 |
2.44 |
2.02 |
39 (3) |
|
10-Jul-99 |
91.59 |
87.7 |
91.61 |
87.91 |
2.75 |
2.39 |
2.66 |
2.16 |
43 (3) |
|
8-Aug-99 |
91.44 |
87.61 |
91.78 |
87.91 |
2.57 |
2.3 |
2.38 |
2.01 |
47 (3) |
|
4-Sept-99 |
91.45 |
87.21 |
92.35 |
87.84 |
2.81 |
2.42 |
2.55 |
2.09 |
51 (3) |
|
3-Oct-99 |
91.31 |
86.96 |
91.56 |
87.06 |
3.21 |
2.61 |
3.09 |
2.55 |
55 (3) |
|
30-Oct-99 |
90.96 |
86.87 |
91.19 |
87.3 |
3.24 |
2.80 |
3.25 |
2.45 |
59 (3) |
|
29-Nov-99 |
91.08 |
86.7 |
|
|
3.64 |
3.28 |
|
|
63(3) no cleaning |
|
23-Dec-99 |
90.52 |
86.39 |
91.84 |
87.42 |
4.04 |
3.48 |
3.62 |
2.75 |
67 (3) |
|
22-Jan-00 |
|
|
|
|
|
|
|
|
71 no data taken |
|
6-Feb-00 |
87.88 |
84.63 |
88.98 |
85.63 |
5.57 |
4.86 |
5.14 |
4.05 |
73 (3) |
|
17-Mar-00 |
87.34 |
84.27 |
88.1 |
85.18 |
5.55 |
5.03 |
5.35 |
4.25 |
78 (3) |
|
21-Mar-00 |
88.3 |
84.69 |
92.66 |
89.03 |
5.62 |
4.68 |
2.20 |
1.09 |
78(3) WASH |
|
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See the efficiency plots of the CO2 cleaning: reflectivity and scattererometry. Average gain per cleaning session is R+0.70% and SC-0.30% in the visible.
2 SEPTEMBER 98: Aluminizing, see the plot of reflectivity and scattering before and after aluminizing (last one was in Apr 97).
B/ SECONDARY MIRRORS
Aluminized together on August 26, 1999. Measurements with the Minolta.
See the F/13.5 mirror reflectometry and scatterometry.
See the F/7.5 mirror reflectometry and scatterometry.
Last update: 18 April 01
