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Tue Nov 20 10:11:33 2007
PMC pole measurements
We measured the PMC pole in the following way.
1. Reduced laser power by rotating lambda/2 plate at laser output. Thermal effects in the PZT distort resonance peaks. Reducing power too much leads to problems with digitisation error.
2. Sweep NPRO PZT (C1: PSL-FSS_INOFFSET) using trianglewave. Record ramp, PMC transmission and reference cavity transmission ('C1: PSL-FSS_FAST','C1: PSL-ISS_INMONPD_F','C1: PSL-FSS_RCTRANSPD_F).
3. Since the PZT cannot sweep a full FSR in the PMC we looked at the sideband resonances within the reference cavity to calibrate the actuator.
Result: 7.35 +/- 0.22 MHz/V
4. Use #3 to calibrate the x axis of the PMC transmission.
5. Fit PMC resoances to an Airy function to get finesse. Take an average, weighted according to the resnorm. Calculate cavity pole frequency.
Result: 380kHz +/- 59kHz.
This corresponds to a finesse of ~936. According to
the nominal pole is at 488kHz and the finesse is 732.
This is by no means a definitive measurement due to the misshapen resonance peaks recorded.