4.0-m Victor Blanco Telescope Reflectometry Data

[As part of the move to the NOIRLab web site, this page is not to be migrated and its contents have been archived in https://www.ctio.noao.edu/cgi-bin/DocDB/ShowDocument?docid=1404]

A recent summary of reflectometry data

Measurements of the reflectivity and total integrated scattering of the Blanco primary mirror (M1) and f/8 secondary mirror (M2) are periodically taken and archived to monitor the quality of the telescopes reflecting surfaces. Currently, measurements are taken with an Iris 908RS scattero-reflectometer during mirror washings (every few months) and aluminizations (less often).

Here is the most recent memo by Daniel Holck on the reflectivity data for the Blanco Telescope:

Blanco Reflectance Log: March-November 2011

Recent measurements (2011) for the Blanco primary mirror M1 show that the reflectivity in the blue (470-530nm) is 92% after aluminization, and slightly lower at redder wavelengths (90% @ 650nm, 88% @ 880nm). Reflectivity tends to decrease ~0.3-0.6% per month afterwards, depending on wavelength. Recent mirror washings appear to increase the blue reflectivity ~0.3-1.0%. The reflectivity of the Blanco f/8 secondary mirror M2 is measured less often, but given its position and baffling, it is much more protected from dust and less variation has been measured. M2 was aluminized in 2001, and recent washings took place in 2007 and 2010. The M2 mirror's reflectivity is typically ~90% in the blue optical (470-530nm) after a wash.

What follows are archival measurements of the Blanco mirrors for the period 1998-2010, and associated documents and figures.

A/ Primary mirror :

AUGUST 00 - NOW: reflectivity and scattering

The measurements were interrupted between November 00 and February 01. Monthly variation rates (over the last 8 months) are: R -0.34% and BRDF(-15) +0.24%. The scatter in the reflectometry plot since February is not well understood, although it might be partly due to the summer seasonal effect (high humidity and thus unstable measuring conditions?).

 

FEBRUARY 01:

in-situ washing. Iris reflectometry and BRDF data before/after wash was respectively:

* 89.6/93.5% (470nm), 89.6/93.6% (530nm), 86.3/89.8% (650nm), 85.1/89.0% (800nm)
* 2.66/0.21% (+20deg), 2.36/0.33% (-15deg), 0.47/0.24% (-45deg)

 

AUGUST 00:

Aluminizing. Iris Reflectometry and BRDF data before/after the coating was respectively:

* 70.6/92.6% (470nm), 71.7/93.0% (530nm), 70.1/89.3% (650nm), 72.2/88.0% (800nm)
* 11.4/0.13% (+20deg), 13.1/0.25% (-15deg), 1.02/0.03% (-45deg)

Before the coating process started, we noticed a strong reflectivity discrepancy between the Minolta and Iris measurements, of the order of 10% (Iris: 71.7% vs. Minolta: 81.5% at 530nm), which becomes much less for the fresh Aluminium (Iris: 93.0% vs. Minolta: 93.6%).

 

AUGUST 98 - AUGUST 00:

Regular CO2 cleaning (twice per month)

All data taken with the Minolta. See the plots corresponding to the entire period: reflectivity and scattering.

Yearly variation rates are R -2.5% and SC +2.0%, in agreement with what is measured at the 1.5m. A seasonal trend seems to show up, as is the case for the 1.5m.

Below is a table of the 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 23Dec98), 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 cleaned and measured just before realuminizing.

From 17 April 99 to August 00, we sampled the same 3 points marked on the mirror (the sampling points were random up to that date). On 18 Sept 99, we changed the edge sampling point.

 

Date % Reflectivity
before CO2
cleaning		 % Reflectivity
after CO2
cleaning		 % Scattering
before CO2
cleaning		 % Scattering
after CO2
cleaning		 Elapsed time
(week)
between
new Al and CO2
 
  400nm 700nm 400nm 700nm 400nm 700nm 400nm 700nm  
7-Aug-98 81.68 78.56 93.88 89.6 8.32 8.75 0.58 0.33 new
aluminium
25-Aug-98 92.6 88.83 92.82 89.16 0.70 0.61 0.73 0.55 2 (1)
10-Sep-98 91.99 88.55 92.88 89.05 0.91 0.73 0.73 0.56 4 (1)
30-Sep-98 92.33 88.53 92.34 88.64 1.12 0.86 0.92 0.73 7 (1)
14-Oct-98 93.59 88.71 93.83 88.68 0.93 0.82 0.78 0.66 9 (1)
29-Oct-98 91.81 88.66 90.97 88.22 0.69 0.61 0.94 0.70 11 (1)
12-Nov-98 90.96 88.06 90.45 87.96 1.09 0.95 1.12 0.83 12 (1)
26-Nov-98 91.19 87.75 90.4 87.31 1.40 1.21 1.55 1.07 15 (2)
12-Dic-98 90.87 87.45 91.28 87.87 1.94 1.45 1.1 0.92 17 (3)
23-Dic-98
+/-		 92.57
0.51		 88.33
0.30		 92.69
0.78		 88.51
0.39		 1.30
0.19		 1.19
0.09		 1.20
0.25		 1.00
0.21		 19 (4)
10-Jan-99
+/-		 90.78
1.83		 87.2
1.19		 91.58
1.02		 87.96
0.40		 1.83
0.60		 1.56
0.19		 1.56
0.20		 1.29
0.14		 21 (4)
23-Jan-99 90.8 87.03 90.95 87.55 2.29 2.03 2.04 1.52 23 (3)
5-Feb-99 91.11 87.59 91.41 87.76 1.92 1.64 2.02 1.55 25 (3)
19-Feb-99 89.94 86.42 90.3 86.67 2.86 2.59 2.68 2.35 27 (3)
6-Mar-99 89.51 86.32 89.82 86.61 2.98 2.42 3.18 2.45 29 (3)
19-Mar-99 90.25 86.94 90.48 87.04 2.75 2.19 2.68 2.12 31 (3)
3-April-99
+/-		 89.62
1.03		 86.23
0.45		 90.31
0.77		 86.51
0.23		 3.62
0.81		 2.9
0.39		 3.15
0.07		 2.77
0.10		 33 (3)
17-April-99 90.4 86.93 90.55 87.14 2.88 2.25 2.75 2.00 35 (3)
1-May-99 89.85 87.07 88.88 85.82 2.6 2.02 2.82 2.09 37 (3)
15-May-99 89.79 86.85 89.81 86.97 2.95 2.15 2.87 2.12 39 (3)
30-May-99 89.45 86.69 89.75 86.92 2.94 2.2 2.86 2.06 41 (3)
13-Jun-99 89.83 87.01 89.69 87.05 2.76 2.04 2.92 2.07 43 (2)
10-Jul-99 89.7 86.78 89.47 87.14 - - 2.81 1.99 47 (2)
23-Jul-99 89.48 86.56 89.74 87.06 2.99 2.15 2.91 2.07 49 (2)
8-Aug-99 88.35 86.55 88.51 86.62 3.0 2.17 3.02 2.14 51 (2)
22-Aug-99 88.82 86.31 88.69 86.3 3.12 2.29 3.01 2.15 53 (2)
4-Sep-99 89.3 86.4 87.89 85.31 3.15 2.25 3.68 2.45 55 (2)
18-Sep-99 89.6 86.37 89.2 86.24 2.95 2.32 3.15 2.38 57 (3)
3-Oct-99 88.56 85.61 88.87 86.02 3.21 2.47 3.36 2.43 59 (3)
15-Oct-99 89.9 87.01 89.79 86.89 2.83 2.1 3.13 2.29 61 (3)
30-Oct-99 88.91 86.09 89.23 86.42 3.22 2.46 3.24 2.35 63 (3)
12-Nov-99 88.72 85.97 88.77 86.08 3.38 2.57 3.33 2.47 65 (3)
29-Nov-99 87.66 85.26 87.85 85.36 4.36 3.35 4.27 3.21 67 (3)
10-Dec-99 87.83 85.22 87.48 85.2 4.11 3.23 4.24 3.11 69 (3)
23-Dec-99 87.67 85.06 88.12 85.43 4.82 3.64 4.42 3.31 71 (3)
7-Jan-00 85.67 83.43 86.32 83.94         no cleaning
(interp)
22-Jan-00 83.67 81.8 84.51 82.44 7.43 6.01 7.22 5.77 75 (3)
5-Feb-00 83.49 81.88 84.04 82.31 7.50 5.95 7.29 5.67 77 (3)
interpolated
22-Feb-00 83.31 81.96 83.57 82.18 7.57 5.89 7.36 5.57 79 (3)
interpolated
3-Mar-00 83.12 82.06 83.1 82.04 7.64 5.82 7.44 5.48 81 (3)
17-Mar-00 82.36 81.18 82.95 81.92 8.48 6.56 8.05 5.93 83 (2)
31-Mar-00 83.04 81.6 83.2 81.73 7.93 5.96 8.02 6.05 85 (3)
13-Apr-00 82.39 80.99 82.27 81.02 8.51 6.37 8.60 6.34 87 (3)
30-Apr-00 82.91 81.88 83.03 82.13 8.34 5.95 8.13 5.75 89 (3)
10-May-00 81.02 79.8 81.11 80.67 10.18 7.99 9.68 7.03 90 (2)
27-May-00 82.82 81.87 82.76 81.89 8.02 5.93 7.71 5.70 91 (3)
11-June-00 82.22 81.04 81.98 81.35 8.81 6.79 8.85 6.45 93 (3)
23-June-00                 No cleaning
6-July-00 81.88 81.26 81.82 81.17 8.68 6.28 8.86 6.44 97 (3)
22-July-00 80.76 80.58 82.31 81.41 9.39 6.73 8.24 6.16 99 (3)
22-Ago-00 100 100 100 100 100 100 100 100 99 (3)

Here are efficiency plots of the CO2 cleaning: reflectivity and scattererometry. Average gain per cleaning session is R+0.36% and SC-0.28% in the visible.

 

AUGUST 98:

See the plots for before washing and after realuminizing (note: the mirror had not been cleaned at all since early 1997). Data with the Minolta.

 

2/ SECONDARY MIRRORS:

# F/8 M2: last aluminized on 31 January 01. Iris reflectometry and BRDF data before/after coating was respectively:

* 80.7/90.3% (470nm), 81.6/90.5% (530nm), 80.8/88.2% (650nm), 80.1/85.5% (800nm)
* 6.9/0.2% (+20deg), 6.3/0.2% (-15deg), 0.2/0.03% (-45deg)

Blanco R&S follow up

Blanco Follow up January 2010

Last update: 23 November 2011 by Eric Mamajek