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David Notebook: Difference between revisions
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==Things to Do/Check==
*Does the cloth transmit significantly more of either 1064 or 1555?
*Try colored glass filters to block 1555. More tests to show light is 633--use chopper at low frequency and look by eye for flashing. Evacuate cavity--is there still light? Is there still noise when locking? (Shouldn't be if the noise is 1555 like we think).
Putting the cavity mirror in front of the PVC pipe drops the signal by a factor of 50 to .4 nW (was I off by a factor of 10 when I checked with gas in the cavity? I don't think so, but maybe recheck).
Since the signals when locking don't seem to be from 633, the .4 amps/watt value I've been using for the photodiode to calculate powers is probably incorrect. For 1064, it is closer to .25 (so powers are actually higher), and it is unrated at 1555. Still, the relative power drops are useful.
Removing the cavity mirror and completely blocking the PVC opening with a book still let through about .25 nW, so actually when the cavity mirror is in place about as much light gets to the photodiode from the PVC pipe as from through the cloth. Maybe it's time to make a better case for the photodiode. Still, since the book cuts down the signal by a factor of 80, most of the light does enter through the PVC pipe opening. Does the cloth transmit significantly more of either 1064 or 1555?
So at least some of the locking signal is from 1064, and some is likely to be 1555 as well. The cavity mirror helps and other filters probably would as well, but it still seems the best option is to use the beam chopper.
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