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[[attachment:BHD_layout_options.pdf|Schematic BHD layout options]] [[attachment:BHD_layout_options.pdf|Schematic BHD layout options]]. In the linked document, some options for placement of the BHD optics are schematically sketched (but I don't consider the option of adding a new table). Some more discussion may be found in [[https://nodus.ligo.caltech.edu:8081/40m/14148| this elog]]

Balanced Homodyne Detection

Requirements

  1. Displacement noise of OMC/LMC mirrors
    • Are we using a single cavity or two?
  2. Scatter loss in mirrors
    • This will affect the backscatter into the IFO
    • This will limit the transmissivity of the cavity for a given finesse.
  3. Cavity design: triangle, quad ring, quad zig-zag (reference the new OMC paper from Koji)
    • What does this mean?
  4. Laser amplitude / frequency noise including DC offsets in various other lock points and motions to simulate bilinear noise
  5. Oscillator noise: AM / FM
    • This will set the requirement on the filtering necessary.
  6. Aux length noise: MICH/PRC/ SRC
  7. Req. on offsets/asymmetries: arm finesse, arm reflectivity, mass imbalance of ETMs
  8. Phase noise of LO
    • This will set the requirement on whatever we use to control the homodyne angle.
  9. Polarization stability requirement for polarization BHD
    • i.e. let's say we have some finite Ip/Is ratio. What does this mean for the readout in signal-referred units?
  10. Backscatter
    • RIN on the LO
    • Phase noise due to motion of the mirrors
  11. Pointing
    • If we opt to not use a mode-cleaner for the LO field, what is the pointing requirement on whatever option we choose?
  12. Suspension
    • What kind of suspension(s) are we planning to use?

    • VOPO and OMCS seem too big to fit on any of our existing tables.

  13. Control scheme
    • How will we control the LO phase?

Layout options

Schematic BHD layout options. In the linked document, some options for placement of the BHD optics are schematically sketched (but I don't consider the option of adding a new table). Some more discussion may be found in this elog

Action items

  • Design SRC so that
    1. Suppress 02/20 modes
    2. Partially transmit 01/10 modes for AS WFS
    3. Suppress thermally generated modes
    4. After the above have been satisfied, choose transmission to maximize ponderomotive squeezing
  • Budget above noises, but especially investigate polarization stability.
  • How is homodyne angle controlled?
  • Beam routing
    • Where to pick off LO?
    • Can we use ETMX transmission for LO? (Koji is crazy)
  • A+ BHD noise budget for both baseline double OMC and polarization BHD.
  • Can we add a heater back to OMC mirror to control ROC? How should the temperature be sensed and controlled?
    • Heater below breadboard for cavity length control

    • Heater on back of mirror for RoC Control

    • Offload PZT DC voltage to slow servo (breadboard heater) to always keep PZT in the middle of the range

Modeling/Noise Budget

  • Some BHD modeling is done in the OptimalGWextraction repo here.

Polarization BHD

Balanced Homodyne Detection (last edited 2020-04-29 17:41:39 by JonathanrichardsonATligoDOTorg)