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Nick Brewer: Difference between revisions
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'''<big>2/8/17</big>'''
Some RF power from the VCO seemed to be getting through even when it was not being triggered by the delay box. Also, when the VCO was connected to the 15 V supply it seemed to add noise to the SHG error signal. So I took it out and now I'm just using the RF generators to look at one frequency at a time.
I think the backburned peak I'm trying to see EIT on is too wide. A rough calculation is showing that the EIT peak should be a couple kHz wide, and the backburned peak is closer to 4 MHz. I'm trying to narrow it by adjusting the time and power that go into creating it.
It's difficult to get more than ~1.4 W of green light from the SHG cavity and have it be stable for a while.
The best bet might be focusing the beams tighter to get more intensity in the EIT beam.
'''<big>1/30/17</big>'''
I try to keep the maximum RF power going into any AOM less than 5 W (37 dBm).
The control and repump beam are coupled into the same fiber using a polarizing beam cube and a polarization maintaining fiber. The output of the fiber is sent through a glan taylor polarizer and a 1/2 wave plate. The probe is also sent through a fiber with a glan taylor and 1/2 wave plate at the output. There is about a microwatt of repump and probe power. I have seen
The two beams are directed parallel to each other, but horizontally displaced by ~3/4 inches, and sent through a 200 mm lens so that they focus and overlap each other in the crystal. This geometry is used so that the probe can be separated from the control/repump beams. There is another 200 mm lens on the other side of the crystal to recollimate the beams.
I keep the cryostat between 4.5 K and 5 K mostly by adjusting the pressure in the dewar. I try to keep the pressure around 3 psi, and at this pressure the cryostat is around 5 K. Over the course of a few hours the pressure gets closer to 6 psi at which point the cryostat is usually close to 4.5 K. At that point I vent it back to 3 or 4 psi.
I have a Matlab program that controls the delay box and the RF generators to the probe, control, and repump beams.
RF3 is the control
An RF switch changes the input to the probe to a VCO instead of the RF generator. An integrator integrates a 10 microsecond pulse from the delay box to create a triangle wave, which is used as the tuning voltage of the VCO. The circuit is built so that the offset and amplitude of the triangle wave can be adjusted by potentiometers, therefore changing the range that the VCO scans over.
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