40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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Message ID: 253     Entry time: Wed Aug 4 10:56:04 2010
Author: Megan 
Type: DailyProgress 
Subject: Optics Set Up! 

All of the optics were set up in the path of the transmitted light from both cavities. Each path needed both a quarter wave plate and a half wave plate to be able to get the s polarization needed by the beam splitter. This solved problems we had earlier with the 50/50 beam splitter doing more like 25/75!

For mode matching, 2 lenses were placed in the path of the RCAV, one with a focal length of 175mm at a distance of roughly 7.5 inches from the first mirror and the other with a focal length of 200mm roughly 5.5 inches before the second mirror. This gave a waist of 224 µm 7.5 inches after the beam splitter.

The ACAV got only 1 lens, with a focal length of 200mm, 2.5 inches before the second mirror, with a waist of 208 µm at the same distance (7.5 inches from the beam splitter).

The first photodetector was placed with a mirror (for better alignment) above the beam splitter, and the other was placed after 2 mirrors and another lens in the other path. The second photodetector has a smaller detector area, so we ideally would like the waist at the detector to be under 100 µm. To make the beam smaller, we used another lens with a focal length of 30mm roughly 2 inches after the second mirror. This still leaves the beam a little larger than we'd like (it's very sensitive to alignment), but it will be fine for the moment.

The two cavities have still not been intentionally locked simultaneously. Yesterday, they differed by roughly 17 MHz (if I remember correctly) and so they were being heated overnight so their temperature can stabilize and we can see if they are closer today.

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