40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Entry  Thu Oct 13 23:58:38 2011, Koji, Update, LSC, fixing REFL165  PA131612.jpgPA131618.jpg
    Reply  Sat Oct 15 16:42:08 2011, Koji, Update, LSC, Testing REFL165  REFL165_test_111014_KA.pdfREFL165_transimpedance2.pdf
       Reply  Sat Oct 15 17:06:20 2011, Koji, Update, LSC, Installation REFL165  
       Reply  Sun Oct 16 02:30:00 2011, rana, Update, Electronics, Testing REFL165  
    Reply  Wed Mar 1 17:25:28 2017, Steve, Update, LSC, MCREFL condition pictures IMG_3646.JPGmcRefl_1.jpgmcRefl_3.jpgmcRefl_5.jpg
       Reply  Fri Mar 17 14:49:09 2017, gautam, Update, LSC, MCREFL condition pictures IMG_7219.JPGMCREFL_X.pdfMCREFL_Y.pdf
Message ID: 12891     Entry time: Fri Mar 17 14:49:09 2017     In reply to: 12860
Author: gautam 
Type: Update 
Category: LSC 
Subject: MCREFL condition pictures 

I did a quick measurement of the beam size on the MC REFL PD today morning. I disabled the MC autolocker while this measurement was in progress. The measurement set up was as follows:

This way I was able to get right up to the heat sink - so this is approximately 2cm away from the active area of the PD. I could also measure the beam size in both the horizontal and vertical directions.

The measured and fitted data are:


The beam size is ~0.4mm in diameter, while the active area of the photodiode is 2mm in diameter according to the datasheet. So the beam is ~5x smaller than the active area of the PD. I couldn't find anything in the datasheet about what the damage threshold is in terms of incident optical power, but there is ~100mW on th MC REFL PD when the MC is unlocked, which corresponds to a peak intensity of ~1.7 W / mm^2...

Even though no optics were intentionally touched for this measurement, I quickly verified that the spot is centered on the MC REFL PD by looking at the DC output of the PD, and then re-enabled the autolocker.

Attachment 2: MCREFL_X.pdf  17 kB  | Hide | Hide all
Attachment 3: MCREFL_Y.pdf  17 kB  | Hide | Hide all
ELOG V3.1.3-