40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  Cryo Lab eLog  Not logged in ELOG logo
Entry  Wed Oct 20 11:31:06 2021, shruti, Update, PSOMA, Towards locking PSOMA with cantilever 
    Reply  Tue Oct 26 10:01:54 2021, shruti, Update, PSOMA, Towards locking PSOMA with cantilever TiltedCantilever.pdfcantileversurface.pdfclampsurface.pdf
       Reply  Thu Nov 18 11:09:24 2021, shruti, Update, PSOMA, Towards locking PSOMA with cantilever CavitySetup.pdfGeometry01.jpeg
          Reply  Wed Dec 1 13:21:54 2021, shruti, Update, PSOMA, Towards locking PSOMA with cantilever IMG_1250.pngIMG_1252.pngIMG_1251.pngIMG_1253.pngIMG_1254.png
             Reply  Thu Dec 2 13:40:57 2021, shruti, Update, PSOMA, Progress and cavity parameters/ lock parameters 
Message ID: 2830     Entry time: Thu Dec 2 13:40:57 2021     In reply to: 2829
Author: shruti 
Type: Update 
Category: PSOMA 
Subject: Progress and cavity parameters/ lock parameters 


Videos of flashes and a very noisy lock.

In Attachment 1 and the video showing a lock, the PDH signal essentially goes to its rails. Most of the noise is in oscillations that are roughly at 143 kHz.


Cavity and Lock Parameters

This elog (2815) shows the cantilever with its mount and a top view of the cavity.


  • FSR: ~ 600 MHz
  • Finesse: [Input coupler transmittance: <4% , Cantilever transmittance:]. Check polarization - measure Finesse for both.
  • cavity pole: also depends on polarization
  • DC optical gain (measured as the PDH slope): W/m, W/Hz



  • Laser resistance->temperature conversion chart
  • Laser temp->frequency to be measured using beat (has not been done consistently in the past since it varies with current)
  • Actuation Coefficient
  • Signal path calibration (first should optimize demod phase)
    • New Focus 1811 40,000 V/A, ~0.85 A/W ?
    • Mixer conv loss: 5 dB
    • 50 Ohm term before LP (6 dB attenuation)
    • compare the W/m calibration to expectation based on:
      • input laser power
      • RF modulation depth
      • cavity Finesse
  • LB lock box transfer function with & w/o Boost engaged.
  • Useful dynamic ranges
    • LB box input stage: +- 10 V. The input stage is a difference amplifier buffer, allowing +- 10 V common mode signals to be subtracted before the filter stage
    • LB box filter stage: +- 330 mV
    • LB box summing stage: +- 10 V
    • LB box output drive: +- 20 mA or +- 10 V
    • ITC 502 current modulation input: +- 10 V
  • Measure transfer functions of laser
    • Measure ITC current driver separately, then ITC+laser
    • Measure phase response using beat and phase lock


ELOG V3.1.3-