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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'''
Generating the (probable) 633 seems repeatable. David found it yesterday morning without having to realign the 780 to the 1064. He lost it later in the day, but was able to realign things and find it again. It seems brighter than ever. (He turned up the 780 tapered amp some.)
David coupled the beam that goes through the dichroic through a multimode fiber, and when the modulation is on, you can see some modulation in frequency in the light that it is transmitted. (It's not really flashing in the sense that it never goes to low brightness; the intensity definitely fluctuates visibly, though.) We can see this by eye, but we are still unable to detect it with the power meter or OSA.
We borrowed a filter centered at 630nm from John Boffard from CC Lin's group, and with that filter in front of the fiber coupler, the flashing through the fiber is more pronounced. The flashing light seems to be a larger fraction of the light, and the constant background seems to be cut down.
Looking at the spectrum analyzer, it seems that the "other red" we saw on 5/16 was probably ASE from the 780 tapered amplifier that has a wavelength outside of the range of the notch of the 780 notch filters.
'''5/16/2014'''
We almost certainly saw 633! We couldn't see it on the spectrum analyzer yet, so I'm not 100% sure, but I'm about 98% sure it's real.
We were able to see a bright red beam that did all of the following:
-
-seemed to correspond with the resonance peaks of the cavity▼
-
▲--seemed to correspond with the resonance peaks of the cavity
--seemed to correspond with the turning on and off of the modulation RF
It was a bit confusing, though, because in addition to the (probable) 633 that has the above characteristics, you can still see other red light coming from the prism. This other red light is constant in intensity, in contrast to the 633. I'm not sure exactly what is from, but it must be from the 785 beam. Maybe it is diffuse scattered light from the reflections of the (small amount of) 785 that reaches the prism. At its best, the 633 was seen to be at least as bright as this other constant beam, if not brighter. The 633 seemed to be coming from the same location on the prism as this other beam, though it was visible when the prism was viewed at a slightly different angle.
We initially overlapped the transmitted 785 (through the dichroic) and the generated 807 that also is transmitted through the dichroic. We did this with the Newport camera.
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