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FMCG/Operating procedure: Difference between revisions
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→Absorption Scan
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# Now return to the rear of the rack and, after verifying the probe tapered amplifier TEC 2000 temperature controller is enabled, enable the probe tapered amplifier output by pressing the '''output''' button on the Newport Model 560B driver. The drive current on the TA sets the eventual light intensity on the detectors. Historically, we have worked with currents as high as 1200 mA, though recently we have worked at much lower values around 750 mA, which delivers ~500 μW of laser power through a hot cell to the detector.
# Once the TA is enabled and light is being sent to the detectors, adjust the gain settings on the I-V converters appropriately. 100-200 uA/V is usually appropriate for the laser powers mentioned above.
# At this point, the detector sum signals should be visible on the scope. The signals should be pretty constant over time. If you notice non-periodic "noise" on this signal, it's possible the beam alignment between the TA and the fiber input is poor. While monitoring the signal, go behind the rack and walk the beam using the two mirrors on the second shelf from the top.
# Once the coupling is optimized, the laser can be scanned across the resonance to measure absorption. The detuning can be scanned by varying the temperature of the diode in one of three ways:
## The temperature can be set manually by pressing '''Set''' on the TEC half of the controller and entering a numerical value with the keypad followed by '''Enter'''.
## After '''Set''' is pressed, pressing the '''Live Entry''' button will allow the user to slowly ramp the temperature by turning the knob next to the '''Live Entry''' button.
## The controller can be controlled using the GPIB connector on the back. This is done using a LabVIEW program, which is what will be described below.
# In the '''FPGA Magnetometer.lvproj''' project, open the '''Laser Scan v1.1''' program under the '''Main Programs''' folder. By default, the program is set up to take an absorption scan with the probe beam:
## '''Differential''' should not be enabled.
## The light next to '''Scan Probe''' should be bright green.
## With the resonance at roughtly 7 kΩ, ramping the temperature from 5 kΩ t
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