1.5-m Reflectrometry

1.5-m Telescope reflectrometry data

A/ PRIMARY MIRROR:

3 APRIL 01:

Reflectometry and BRDF data with Iris:

    •  85.3% (470nm), 85.7% (530nm), 83.1% (650nm), 82.5% (880nm)
    •  4.6% (+20deg), 4.3% (-15deg), 2.0% (-45deg)

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):

    •  83.1/92.4% (470nm), 83.7/92.7% (530nm), 80.7/89.1% (650nm), 81.1/89.0% (880nm)
    •  4.8/0.1% (+20deg), 4.3/0.2% (-15deg), 5.1/0.02% (-45deg)

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:

    •  91.5% (470nm), 91.8% (530nm), 87.5% (650nm), 87.6% (880nm)
    •  0.2% (+20deg), 0.2% (-15deg), 0.02% (-45deg)

 

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-Feb-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 87.34 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

 

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

 

Follow-up November 2009