Coating measurement results

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e-mail from Helena summarizing  REO and Caltech measurements of Beam Splitters

email from Mike Landry to Mike Zucker describing the measurement and results -  For 670 nm probe beam
Sender: mlandry@ligo-wa.caltech.edu
Date: Thu, 11 May 2000 19:18:09 -0700
From: Michael Landry <landry_m@ligo-wa.caltech.edu>
Organization: LIGO Hanford Observatory
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To: Mike Zucker <zucker_m@ligo.mit.edu>
CC: Helena Armandula <armandula_h@ligo.caltech.edu>
Subject: measurements of witness samples

Hi Mike, 

Ok, here's the data on the witness samples I've been looking at. 

Gary Traylor indicates that the identity of the LLO core optics is as follows: 
    ETMx    SPETM07-A 
    ETMy    SPETM05 
    RM        RM04-B 
    BS          BS04 
    ITMx      4ITM03-C 
    ITMy      4ITM02-C 

Thus, careful measurements were made of the witness samples associated with these optics.  I confirmed the identity of each HR sample with the 1064nm laser on ISCT10 (many of the samples have both the AR and the HR piece in the box).  Each sample was cleaned with C02.  The input power was monitored, and it never deviated in any significant way. 

The behaviour of the samples was different.  Samples for the BS and RM had reflectivities that varied smoothly with angle; no precipitous drops.  However the others (ITM, ETM and FM) had structure, particularly in the 0-25 degree range (at heigher angles, they tended to vary more smoothly).  For instance, for the FM sample, sweeping the optic through a fraction of a degree, just across the face of the power meter at 3', you can see the reflected power go from about 0.8mW, down to 0.2 mW, and then back up to 0.8 or so.  I've made a measurement every degree, but this is still a coarse sampling and to really pull out the structure you would have to measure to the tenth of a degree.  I searched for zeros on each sample, where the reflectivity vanished, but did not find any.  The plots represent an accurate range of reflectivites (e.g. the FM reflectivity never seems to drop below that 0.2mW value). 

I've included the eps files attached to this message.  They are also available at my file section if you prefer ( http://www.ligo-wa.caltech.edu/~mlandry ).   Let me know if you want the raw data and I can send it to you. 

Salut, 
Michael 

-- 

Michael Landry
LIGO Hanford Observatory
P.O. Box 1970
Mail Stop S9-02
Richland, WA
U.S.A.  99352

phone 509-372-8133
fax   509-372-8137

Beam Splitter and Folding Mirror
Input Test Mass and End Test Mass
Recycling Mirror