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David Notebook: Difference between revisions
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==Daily Log==
'''7/9/14'''
Testing the 633 filter showed it lets through about 90% of 1555.
'''7/8/14'''
Pumped down the cavity in case some nitrogen had leaked in over the last few weeks. Re-added deuterium to about .3 atm. Noted that the .5 nW signal when locking the cavity is present even when the path from the diffraction grating to the photodiode is blocked. The locking signal looks about the same size whether or not the path is blocked, although the offset is different. There is no noticeable difference with the 780 on or off. I tried blocking off part of the optical table at beam level, but this didn't affect the .5 nW signal. It seems that the signal is almost definitely due to scattering. The 633 bandpass filter we use is not rated at 1555, so it may be letting through significant amounts of light at this wavelength. This could explain why the signal was present when locking even with the filter in place if the signal is from scattering. Putting in the cavity window in front of the PVC pipe reduced the locking signal by about a factor of 5 both with the beam path to the detector blocked and unblocked.
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