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Entry  Mon Oct 26 19:10:59 2015, gautam, Update, Green Locking, AUX PDH loop characterization 
    Reply  Tue Dec 8 23:24:08 2015, gautam, Update, Green Locking, Y end laser (Lightwave) PZT calibration Ycalib_8Dec.pdf
       Reply  Sun Dec 13 21:55:28 2015, gautam, Update, Green Locking, Y end laser (Lightwave) PZT calibration IMG_5972.JPGServoY_TF_13Dec2015.pdfDatanCode.zipPSD_916Hz.pdf
          Reply  Mon Dec 14 16:27:11 2015, gautam, Update, Green Locking, Y-end AUX PDH noise breakdown YAUX_NB_Dec2015.pdfPDH_errSig_Calib.pdf
             Reply  Mon Jan 4 16:45:11 2016, gautam, Update, Green Locking, Y-end AUX PDH noise breakdown ErrSigBreakdown.pdfcontrolSigBreakdown.pdfYEnd_PDH_OLTF.pdf
          Reply  Mon Jan 4 16:09:54 2016, gautam, Update, Green Locking, Y end laser (Lightwave) PZT calibration choosingExcFreqs.pdflaserPZTcalib.pdf
Message ID: 11865     Entry time: Tue Dec 8 23:24:08 2015     In reply to: 11715     Reply to this: 11877
Author: gautam 
Type: Update 
Category: Green Locking 
Subject: Y end laser (Lightwave) PZT calibration 


I measured the PZT actuator gain for the Lightwave NPRO at the Y-end to be 3.6 +/- 0.3 MHz/V. This is somewhat lower than the value of 5 MHz/V reported here, but I think is consistent with that measurement. 


In order to calibrate the Y-axis of my Aux PDH loop noise budget plots, I wanted a measurement of the end laser actuator gain. I proceeded to measure this as follows:

  1. Use a function generator to add a DC offset to the error point - I did this by taking the output of the RF mixer -> Input A of an SR560, output of the function generator -> input B of the SR560 (via a 20 Ohm attenuator, and with a 50ohm T-eed to the input for impedance matching), and setting the output to A-B, and feeding that to the "Servo Input" on the PDH box.
  2. I then locked the arm to IR, ran the dither to maximize the green transmission, and set up a beat note at ~39 MHz with the help of the analyzer in the control room.
  3. Set phase tracker UGF, clear phase history.
  4. Vary the DC offset to the error point by using the offset on the function generator. I varied the offset until the green TEM00 lock was lost, in steps of 0.1 V. At each step, I averaged the output of the phase tracker for 15 seconds.
  5. Convert the applied DC offset to the DC offset appearing at the servo output using the transfer function of the servo box (DC gain measured to be ~65 dB), taking into account the 20dB attenuator also.

The attached plot shows the measured data. The X-axis is shown after the conversion mentioned in the last bullet point. The error bars are the standard deviations of the averaging at each DC offset. 

To do:

  1. The value of the DC gain of the servo, 65 dB, is an approximate one based on a rough measurement I did earlier today. I'll take a TF measurement with an SR785 tomorrow, but I think this shouldn't change the number too much.
  2. Upload the noise budget measurements for the Y-end PDH loop.
Attachment 1: Ycalib_8Dec.pdf  83 kB  | Hide | Hide all
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