The results of the AM/PM measurements:

• Attachment 1: Traces of 9 AM TFs overlaid on top of each other, calibrated by measuring the voltage at the ‘GREEN_REFL’ output where the TF was measured (described in elog 40m:15197). This was almost exactly 2 V.
• Attachment 2: Traces of 9 PM TFs also overlaid measured using DLFD (as described in elog 40m:15180). Calibrated using the measured ~600 mV pk-pk voltage. The phase plots were unwrapped (shifted by 180 deg if needed) so that each started from roughly 0 deg.

Both the AM and PM TFs were scaled to make them have the same average value. Manually adjusting the delay line offset for each measurement using the oscilloscope was probably not accurate enough and therefore resulted in different scaling which this should somewhat compensate.

Attachment 3:

• The orange and green lines are the averages of the PM and AM values of Attachments 1 and 2 respectively.
• The solid red line is at 230 kHz, which was the previously chosen value for PDH locking. The peak seems to have shifted to the left from previous measurements (elog 40m:12077).
• A horizontal black dashed line is drawn to show where the ratio is 10^5.
• The red regions correspond to frequencies where PM/AM > 10^5 [only shown for frequencies greater than 200kHz], these are roughly (in kHz):
  • 211.4-213.9
  • 221.4-230.7 (peak at 225.642)
  • 240.8-257.9
  • ~748.3
  • 753.3-799.8, two largest peaks at 763.673 and 770.237
  • 809.6-829.3, peak at 819.472
  • 839.2-842.4
  • 881.8-891.7

Updated Calibration

The new plot is in Attachment 5.

The new calibration factor used: 5 MHz/V at the output of the mixer to obtain the frequency modulation and then division by the mod. freq. to obtain PM.

5 MHz/V because changing the PZT voltage by 0.01 V=> change in beat frequency by 0.1 MHz, which was seen as a 20 mV change in the delay line mixer output.

Again, the calibration is not very precise and I will probably repeat this experiment at some point more precisely.