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Josh Notebook: Difference between revisions
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'''5/22/2014'''
Still unable to definitively isolate and detect 633.
Coming from the cavity, we have the following filtering:
1000nm shortpass dichroic
two 780 notch filters
1 cavity mirror (reflects (thus blocking) 1064 and 1555 extremely well)
John Boffard's 633 10nm-wide bandpass filter
After that, we have the light coupled to a multimode fiber.
We still can't see anything on the OSA. We ''maybe'' can see about 0.2nW on the power meter if we put the fiber right up against it, and then cover everything with dark cloth and cardboard and turn all the lights off. This is definitely reaching the lower limits of what the detector can see, though, so we're not sure. Also, there's no way to be sure that this is 633.
We can definitely see this same signal if we put the same fiber up to one of our "bare" photodiodes (not the pre-boxed kind, the kind where it's just a diode that we soldered up). We send the output of the photodiode to an SRS preamp - (SR 570) - and then we send that signal to the scope. The pre-amp is used to filter out any DC offset of the signal, and it also provides the needed gain. We can easily see this signal on the scope, though we're not sure how much comes from 633. We're sure that it's not all of it because we can see a small portion even when 780 is blocked. However, it is very obviously coordinated with the lock, and the signal is by far (by a factor of 5 maybe) the largest when we have 1064 locked to the cavity and 780 on.
I set up 1/2" apertures after the prism set-up (mentioned 5/16) to make sure we know exactly where the 633 is going. You can see the 633 through the two apertures. I think that I will put a lens in and try to see if I can measure any power there.
'''5/20/2014'''
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