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 [1] (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 [2] and scattering [3] 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 [4] and scattererometry [5]. Average gain per cleaning session is R+0.70% and SC-0.30% in the visible.

2 SEPTEMBER 98:

Aluminizing, see the plot [6] 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 [7] mirror reflectometry and scatterometry.

See the f/7.5 [8] mirror reflectometry and scatterometry.

Last update: 18 April 01

Follow-up November 2009 [9]