I was so lazy that I have not added any entry about the 3days work. So I summarize this week measurements.
1. OLG measurement
We measured the open loop gain of FSS loop on Monday and Wednesday. The UGF was 125kHz on Monday and 75kHz on Wednesday. We are not sure why those UGFs are so different but we realized that the transmitted light power was different. That makes difference about optical gain of Reference cavity and that means it also make difference in the OLG.
2. OLG fitting
I fitted the OLG with modeled FSS control loop. The attached files is the plot of fitted and measured curves on 5/29. I forgot to bring the data of 5/31 from PSL room, so I would upload that curve tomorrow.
3. cavity pole measurement
to measure cavity pole of reference cavity, we added amplitude modulation with FSS AOM and measured the transfer function from Refcav Refl DC PD to Trans DC PD. The result is attached. The cavity pole was estimated as 87kHz.
4. Free run noise estimation.
On Monday, we tried to estimate the free run noise of the NPRO laser frequency, from error signal and open loop gain of FSS loop. But the result of this estimation was larger than typical NPRO frequency noise with factor of 10. And after some discussion, we realized that the error signal is smaller than the detector noise of a FFT analyzer. So we have not measured the error signal but the detector noise of FFT analyzer. On wednesday, we changed the port to measure the error signal from TTFSS servo common OUT1 to OUT2. There is 10dB amplifier between those ports, so with OUT2, we can measure 'the error signal of FSS loop'.
For estimation of free run noise, the open loop gain is needed but I forgot to bring the data as I mentioned. I would upload the estimated free run noise tomorrow.
