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Entry  Wed Jun 13 19:00:26 2012, Sarah, DailyProgress, Laser, Transfer Functions 12x
    Reply  Fri Jun 22 22:34:28 2012, tara, DailyProgress, NoiseBudget, RIN coupling to Frequency noise 
    Reply  Wed Jun 27 18:51:56 2012, Sarah, DailyProgress, Laser, Transfer Functions Slide1.pngtf_oa_calc_measured.pngTF_allfreq.pngTF_fit_allfreq.pngnb_allfreq.png
       Reply  Fri Jul 6 18:59:49 2012, tara, DailyProgress, Laser, Transfer Functions IMG_1447.jpgRIN_Fnoise.pngRIN_Fnoise.png
          Reply  Tue Jul 10 02:55:37 2012, tara, DailyProgress, Laser, Transfer Functions 
             Reply  Mon Jul 16 19:08:34 2012, tara, DailyProgress, NoiseBudget, Transfer Functions (RIN to Frequency noise via photothermal) 
                Reply  Tue Jul 17 19:05:32 2012, tara, DailyProgress, NoiseBudget, Transfer Functions (RIN to Frequency noise via photothermal) 7x
                   Reply  Tue Jul 24 17:02:35 2012, Sarah, DailyProgress, NoiseBudget, Transfer Functions (RIN to Frequency noise via photothermal) 8x
                      Reply  Fri Aug 3 02:46:15 2012, tara, DailyProgress, NoiseBudget, Transfer Functions (RIN to Frequency noise via photothermal) RIN_coupling_2012_08_03.pngRIN_coupling.fig
                         Reply  Tue Aug 13 21:45:51 2013, tara, DailyProgress, NoiseBudget, Transfer Functions (RIN to Frequency noise via photothermal) farsi_2013_08_13.pngfarsi_2013_08_13.figRIN_TO_algaas.pngRIN_TO_algaas.fig
                            Reply  Fri Aug 16 04:35:58 2013, tara, DailyProgress, NoiseBudget, Transfer Functions (RIN to Frequency noise via photothermal) RIN_req_algaas.pngRIN_req_algaas.fig
                            Reply  Thu Aug 22 13:36:19 2013, tara, DailyProgress, NoiseBudget, Transfer Functions (RIN to Frequency noise via photothermal) fasi_2013_08_22.pngFarsi_compare.fig
          Reply  Wed Jul 11 11:13:38 2012, Sarah, DailyProgress, Laser, Transfer Functions 7x
          Reply  Sun Jul 15 23:20:32 2012, tara, DailyProgress, NoiseBudget, Transfer Functions (power fluctuation to Frequency noise via photothermal effect) Farsi_compare.pngFarsi_compare.fig
             Reply  Thu Jul 19 03:01:26 2012, tara, DailyProgress, NoiseBudget, Transfer Functions (power fluctuation to Frequency noise via photothermal effect) Farsi_compare.pngFarsi_compare.fig
                Reply  Thu Jul 19 23:56:45 2012, rana, DailyProgress, NoiseBudget, Transfer Functions (power fluctuation to Frequency noise via photothermal effect) 
                   Reply  Fri Jul 20 01:32:45 2012, tara, DailyProgress, NoiseBudget, Transfer Functions (power fluctuation to Frequency noise via photothermal effect) 
Message ID: 1020     Entry time: Mon Jul 16 19:08:34 2012     In reply to: 1016     Reply to this: 1021
Author: tara 
Type: DailyProgress 
Category: NoiseBudget 
Subject: Transfer Functions (RIN to Frequency noise via photothermal) 

Sarah and I are trying to remeasure the coupling from RIN to frequency noise. Here we list the problems that might cause the error in the measurement.

 Before measuring anything, we aligned the beam to ACAV and RCAV , adjusted the power so the power to ACAV is 2mW and RCAV has 0.2mW.

We found out that:

  1. EAOM alignment does not change the measured TF. We misaligned the EAOM and measured the TF. There was no significant change in the measured TF.
  2. The measured TF does not change with excitation level (from SR785). With output level of 1-5Vpkpk, the measured TF remains the same.
  3. However, the TF changes if we change the power to ACAV. The measure TFs with different power level differ at high frequency and they converge at low frequency depend on the power level. For example, if we choose RFpower on Marconi to 12 dBm, the measured TF will be higher than the TF with 13dBm power ~ 2dB at 1kHz, and converge around 300Hz.

Since the TF remains the same at lower frequency, we thought that the gain of ACAV loop cannot keep up with the frequency noise and cause the deviation in the measure TF, so we checked the UGF of ACAV with different power level (*this is done roughly for a quick check, we will come up with more careful analysis later).

RFpower[dBm] [P_acav mW] UGF
10  [0.4] 16kHz
12.2 [1.3] 39kHz
13 [2.0] 50kHz

The measurements above were done with an extra ND filter that reduce the power on RFPD by a factor of 2. The shape of the TF is roughly 1/f.  The UGF is significantly higher than the interested frequency (DC-1kHz), so we think it is not the insufficient gain in ACAV loop.

So we change the gain in RCAV loop, by increasing the power to 0.4 mW. With this level to RCAV, the TF does not change with power to ACAV that much, unless the power goes down to ~0.4mW.  On the other hands, the TF(RIN coupling) also changes if we reduce RCAV gain to certain level. We will investigate more about this.

Quote:

I tried to remeasure the coupling from RIN to frequency noise (same setup as in psl:1005).  However I have not been able to reproduce the result yet.

 

The result we got in psl:1005 does not have the same TF shape as we expected from the calculation. The slope is off by 1/f^0.25. So There might be something wrong with the setup, for example bad alignment in EAOM that adds PM to the beam and effect the PDH signal. So in order to verify the problem I redo the measurement with the similar setup. This time, however, when I change the power into ACAV, the measured TF changes as well (this did not happen before), so I'm checking what's wrong with the setup.

Checking plan:Once I can remeasure the TF (ACAV AOM feedback/ ACAV TRANSPD). I want to check

  1. effect of beam EAOM alignment to the TF
  2. comparison between TF from (ACAV AOM feedback/ACAV TRANSPD) and (beat signal/ACAV TRANSPD). I tried this already and they are quite similar except some phase shift.
  3. To verify that the measurement is valid, I'll make sure that the TF is independent of excitation level and power input to ACAV.

 

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