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Nick Brewer: Difference between revisions
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'''<big>3/5/15</big>'''
The AOMs are now set up so that the control and probe beams connect the top two ground states to the top excited state and the repumper connects the bottom ground state to the bottom excited state. This way we should be able to leave the repumper on during our experiments in order to continually pump out the unused ground state. I tried to see EIT a few times but was unsuccessful. I tried to replicate Hemmer's papers where they see EIT in Pr3+:YSO, I calculated intensities incorrectly so I was an order of magnitude higher than I thought. I'll fix it and try again. The laser doesn't seem to be as stable as you would guess when it is locked to the invar cavity. It definitely drifts with temperature. The spectral holes still drift a little but not as much as no lock. It might be that we won't be able to see anything until we get the ULE cavity back.
The SHG cavity peaks become distorted around 1 W of input power. Once the cavity is locked the power fluctuates over several hundred mW (depending on the input power). In order to stabilize it you need to adjust the error signal offset, and to a lesser extent the piezo gain, while it is locked. It becomes increasing difficult to lock to and I can't really get a stable lock over ~3.5 W or so. Also, the efficiency drops as the input power increases. Around 1 W we see around 25% efficiency, but it decreases to ~15% closer to 3 W of input power. I am able to get a maximum of 600-800 mW of green, depending on the power meter being used. [http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-18-11-10985 This] paper talks about peak distortion at higher input powers that is pretty much the same thing we are seeing. They say they don't have a problem locking it though. We should be able to produce enough green power for now, but I would like to fix it so we can have a more stable lock at higher powers. Right now I am thinking we should redesign the cavity so that the focus in the crystal is much looser. That way the thermal effects won't be as big of a deal. I think we will be able to loosen the focus and still retain good efficiency. I will run some simulations later to see what will be best.
One of the RF Bay MPA-40-40 4 Watt RF amplifiers seems to not be working right. When we scan the probe the oscilloscope trace doesn't look at smooth as it should be. There is a significant drop in green light at 80 MHz. When I switch amplifiers it looks right. For now I just switched the probe's amplifier and put the malfunctioning one on the repump AOM.
'''<big>2/16/15</big>'''
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