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Entry  Fri Dec 27 16:26:11 2019, Yehonathan, Update, PSL, PMC Linewidth measurement PMCTransmissionSpectra.pdf
    Reply  Wed Jan 1 14:14:00 2020, Yehonathan, Update, PSL, PMC Linewidth measurement 150MHzSideBandCreation.pdfLinewidthMeasurment.pdf
       Reply  Wed Jan 15 15:04:31 2020, gautam, Update, PSL, PMC Linewidth measurement 
          Reply  Fri Jan 17 22:11:19 2020, Yehonathan, Update, PSL, Ringdown measurements 20200117_192455.jpg20200117_192448.jpg
             Reply  Sat Jan 25 11:54:42 2020, Yehonathan, Update, PSL, Ringdown measurements Input_beam_path.jpgReflected_Beam_Path.jpgTransmitted_Beam_Path.jpgPMCRingdownNormalizedRawdata.pdfTransPDFits.pdf
                Reply  Mon Jan 27 21:35:06 2020, Yehonathan, Update, PSL, Ringdown measurements IMC_REFL_Beam_Path.jpg
                   Reply  Mon Jan 27 21:48:49 2020, gautam, Update, PSL, Ringdown measurements elevatedSeis.pdf
                      Reply  Tue Jan 28 16:01:17 2020, gautam, Update, IOO, IMC WFS servos stable again QPD_recenter.png
                         Reply  Tue Jan 28 20:51:37 2020, Yehonathan, Update, IOO, IMC WFS servos stable again 
                            Reply  Wed Jan 29 12:40:24 2020, Yehonathan, Update, IOO, IMC Ringdowns preliminary data analysis IMCRingdownNormalizedRawdata.pdfIMCTransPDFits.pdf
                               Reply  Mon Feb 3 13:54:10 2020, Yehonathan, Update, IOO, IMC Ringdowns extended data analysis IMCTransReflAnalysis_anotated.pdf
                                  Reply  Wed Feb 5 21:13:17 2020, Yehonathan, Update, IOO, IMC Ringdowns extended data analysis 
                                     Reply  Sat Feb 15 12:56:24 2020, Yehonathan, Update, IOO, IMC Transfer function measurement IMCFrequencyResponse.pdfIMCRingdownNormalizedRawdata.pdfIMCREFLPDFits.pdf
Message ID: 15154     Entry time: Sat Jan 25 11:54:42 2020     In reply to: 15132     Reply to this: 15160
Author: Yehonathan 
Type: Update 
Category: PSL 
Subject: Ringdown measurements 

Zero order beam PMC ringdown

On Wednesday I installed 3 PDs (see attached photos) measuring: 

1. The input light to the PMC. Flip-mirror was installed (sorry Shruti) on the beam path to the fiber coupler.

2. Reflected light from the PMC.

3. PMC transmitted light.

I connected the three PDs to the oscilloscope and the AOM driver to a function generator. I drive the AOM with a square wave going from 1V to 0V.

I slowly increased the square wave frequency. The PMC servo doesn't seem to care. I reach 100KHz - it seems excessive but still works. In any case, I get the same results doing a single shut-down from a DC level.

I download the traces. I normalize the traces but I don't rescale them (Attachment 4) so that the small extinction can be investigated.

I notice now that the PDs show the same extinction. It probably means I should have taken dark currents data for the PDs.

Also, I forgot to take the reflected data when the PMC is out of resonance with the laser which could have helped us determine the PMC transmission.

Again, the shutdown is not as sharp as I want. There is a noticeable smoothening in the transition around t = 0 which makes the fit to an exponential difficult. I suspect that the function generator is the limiting device now. I hooked up the function generator to the oscilloscope which showed similar distortion (didn't save the trace)

I try to fit the transmission PD trace to a double exponential and to Zucker model (Attachment 5).

The two exponentials model, being much less restrictive, gives a better fit but the best fit gives two identical time constants of 92ns.

The Zucker model gives a time constant of 88ns. Both of these results are consistent with more or less with the linewidth measurement but this measurement is still ridden with systematics which hopefully will become minimized IMC ringdowns.

Attachment 1: Input_beam_path.jpg  1.798 MB  Uploaded Sat Jan 25 14:20:11 2020  | Hide | Hide all
Attachment 2: Reflected_Beam_Path.jpg  673 kB  Uploaded Sat Jan 25 14:20:21 2020  | Hide | Hide all
Attachment 3: Transmitted_Beam_Path.jpg  2.981 MB  Uploaded Sat Jan 25 14:20:34 2020  | Hide | Hide all
Attachment 4: PMCRingdownNormalizedRawdata.pdf  147 kB  Uploaded Sat Jan 25 17:05:57 2020  | Hide | Hide all
Attachment 5: TransPDFits.pdf  46 kB  Uploaded Sat Jan 25 19:01:04 2020  | Hide | Hide all
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