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Entry  Thu Jul 9 17:12:52 2020, gautam, Update, BHD, In-air BHD OMCchamber.pdfAP_Table_20180328.pdf
    Reply  Tue Jul 14 15:29:25 2020, gautam, Update, BHD, In-air BHD - DCPD amplifier noise DCPDamp.pdf
    Reply  Wed Jul 15 19:11:40 2020, gautam, Update, BHD, In-air BHD - alignment into OMC 
       Reply  Thu Jul 16 01:12:22 2020, gautam, Update, BHD, In-air BHD - preparing the LO path IMG_8626.JPGIMG_8627.JPGIMG_8628.JPGIMG_8629.JPG
          Reply  Sun Jul 19 15:40:15 2020, gautam, Update, BHD, In-air BHD - CDS and wiring summary wiringDiagram.pdf
             Reply  Wed Jul 29 11:57:59 2020, rana, Update, BHD, In-air BHD - CDS and wiring summary 
          Reply  Mon Jul 20 17:55:15 2020, gautam, Update, BHD, In-air BHD - preparing the LO path 
             Reply  Tue Jul 21 00:30:24 2020, gautam, Update, BHD, In-air BHD - LO RIN LO_RIN.pdf
Message ID: 15464     Entry time: Thu Jul 9 17:12:52 2020     Reply to this: 15479   15483
Author: gautam 
Type: Update 
Category: BHD 
Subject: In-air BHD 


We can probably learn something about the interferometer / top level BHD plan with an in-air BHD setup, even if the noise is bad. Here are some thoughts about how we would do it. 

LO delivery:

For this first attempt, we don't really care about the PRC filtering. So possible places to pick off an LO beam are:

LO beam pickoff options
Location Pros Cons
  • Filtered by IMC
  • Medium level of invasiveness  
  • We lose the IP POS diagnostic, which is kind of useful nowadays given the drifty TTs.
  • Only few mW LO power available
PSL table IR beam currently going to green doubling setup
  • Least invasive w.r.t. normal IFO operation
  • Plenty of light (~100 mW) available. But how much can we safely couple into fiber?
  • Beam not filtered by IMC (although it is filtered by the PMC)
  • Since this beam is extracted from inside the PRC, probably enjoys the best filtering.
  • Possibly drifts a lot, so tricky to reliably couple into a fiber?
  • Maximally invasive w.r.t. regular IFO operations.

In all cases, I think the easiest option to actually route whatever beam we choose into a fiber, and then bring it over to whatever cavity we choose to use for an OMC. I'm assuming whatever phase control technique we end up using can cancel the fiber phase noise at relevant frequencies.

LO phase control

  • Stress the fiber? This will require us to purchase some custom hardware, and interface it to the CDS system.
  • PZT mirror? We should have sufficient hardware available to drive a PI style PZT mirror.

There is a question about the range, but I think these are the only two realistic options we can implement on a reasonable time scale.


Again, there are a few options. Here are some pros and cons that come to my mind.

OMC cavity options
Option Pros Cons
Old copper OMC
  • Probably the simplest option in terms of the peripherals.
  • PZT driver recently verified to work
  • We can get the OMMT and DCPDs out as well.
  • Allows us to not compromise on the RF darm optical gain (not sure if locking will be as easy if we cut the power to the AS55 photodiode by 50-75%).
  • Requires a vent.
  • Probably not the most efficient use of the space on the AP table.
  • Filtering performance isn't quantified.
Spare PMC
  • Doesn't require a vent.
  • Compact footprint.
  • Need to build the cavity.
  • Need to check if the drive electronics from the old copper OMC can easily be interfaced with whatever PZT we use on this cavity.
  • Filtering performance kind of unknown?
Custom cavity with spare mirrors
  • Doesn't require a vent.
  • Probably no more difficult than the spare PMC option?
  • We need at least one actuatable mirror, so we'd need some PZT mounted optic + associated drive electronics.

If we can do a vent (we'd just need a single chamber open), I'd go for the option of getting the copper OMC out and using that. Attachment #1 shows the approximate sizes of the various components (OMMT, OMC cavity, DCPDs), while Attachment #2 shows a rough sketch of where things would go on the AP table, with the rectangles approximately to scale.


I'd made a c1omc model sometime ago. Basically, I think we have sufficient ADC/DAC channels in the c1ioo machine for any of the options listed above - but using the copper OMC and associated peripherals would allow the easiest interfacing.

Criticisms/comments/thoughts please.

Attachment 1: OMCchamber.pdf  3.188 MB  Uploaded Thu Jul 9 18:43:38 2020  | Hide | Hide all
Attachment 2: AP_Table_20180328.pdf  20.185 MB  Uploaded Thu Jul 9 18:43:51 2020  | Hide | Hide all
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