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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: 1029     Entry time: Tue Jul 24 17:02:35 2012     In reply to: 1021     Reply to this: 1032
Author: Sarah 
Type: DailyProgress 
Category: NoiseBudget 
Subject: Transfer Functions (RIN to Frequency noise via photothermal) 

Tara and I measured the transfer function coupling RIN to Frequency noise over a wider range of power levels. 

Setup and Measurements:

RCAV power was set to.3mW. We varied ACAV power, and added the rf amplifier mentioned in Elog 1022  after the rfpd to compensate for low power levels. We measured the visibility of the cavity to be 72%, and including this number should slightly  improve the accuracy of the input power level used in calculations. The TF was measured at the following power levels: 2.7mW, .84mW, .32mW, and the results plotted with the TFs measured last week at: 1.6mW, 1.4mW, 1.3mW, 1.2mW, 1.0mW. It should be noted that the visibility was not measured during data collection for the TFs measured last week, so in scaling the power I assumed a visibility of 72%. This may not be perfectly accurate, however as of now it only affects the labeling of the power, since the creation of the following plots does not depend on input power. The upper power limit for measurement was set by the saturation of the photodiode, which we found out saturates at about 10.2V. While inserting a filter after the photodiode would allow us to measure at higher powers, it would also mean we would need to recalibrate, so we just measured up to the saturation of the photodiode for these measurements. 

Data and Results:

The following plot shows the raw data collected for all eight TFs, in dB and degrees:

tf_plot_all.png

The transfer functions appear quite consistent and thus don't seem to depend on the power level. We expected to see more of a common mode effect for the measurements where ACAV power was comparable to RCAV's .3mW power. This effect is apparently absent, and we plan to do further measurements to investigate it further. We also measured the coherence between the AOM feedback signal and intensity noise, as well as frequency responses for the three recently measured transfer functions, as shown below:

Coherence.pngFreq_response.png

A white noise excitation was used for the frequency response and coherence measurements. The coherence was measured to be essentially zero without excitation. It is possible there was an error in measurement for the .32mW measurements, as the frequency response does not seem to follow the appropriate trend, which should be consistent with the magnitude of the transfer function. 

I converted the 2.7mW transfer function magnitude to units of Hz/Watt and plotted it against the calculations using Cerdonio's and Farsi's results:

tf_meas_calc.png

The voltage to power calibration factor is still a main source of error in this conversion. 

Attachment 5: Coherence.fig  43 kB  Uploaded Tue Jul 24 18:38:20 2012
Attachment 6: Freq_response.fig  40 kB  Uploaded Tue Jul 24 18:38:39 2012
Attachment 7: tf_plot_all.fig  55 kB  Uploaded Tue Jul 24 18:40:08 2012
Attachment 8: tf_meas_calc.fig  82 kB  Uploaded Tue Jul 24 18:40:29 2012
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