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Entry  Mon Jul 18 14:20:09 2022, Koji, General, General, OMC #002 Plan Portal 
    Reply  Tue Jul 19 03:17:56 2022, Koji, General, General, OMC #002 Power Budget before mirror cleaning 
       Reply  Thu Jul 21 02:55:06 2022, Koji, General, General, OMC #002 Power Budget after mirror cleaning 
    Reply  Thu Jul 21 14:35:35 2022, Koji, General, General, Bond reinforcement blocks for the invar brackets IMG_1095.JPGIMG_1091.JPG
    Reply  Thu Jul 21 14:55:48 2022, Koji, General, General, Optics bonding for the backscatter measurement IMG_1098.JPG
    Reply  Thu Jul 21 17:47:00 2022, Koji, General, General, The profile of the beam incident on the fiber input coupler fiber_beam_profile.pdf
    Reply  Fri Jul 22 00:31:17 2022, Koji, General, General, OMC #002 backscatter measurement OMC_backscatter.pdf
    Reply  Fri Jul 22 17:47:38 2022, Koji, General, General, C&B request for the reinforcement blocks PXL_20220722_222013127.jpg
    Reply  Tue Jul 26 00:12:58 2022, Koji, General, General, High QE PD: QE measurements IMG_1118.JPG
       Reply  Wed Jul 27 10:34:09 2022, Koji, General, General, High QE PD: QE measurements 2 IMG_1119.JPGIMG_1120.JPG
    Reply  Wed Jul 27 10:09:51 2022, Koji, General, General, 4+4 wire clamp in hand PXL_20220727_072154009.jpg
    Reply  Wed Jul 27 10:34:30 2022, Koji, General, General, OMC #002 Protective FirstContact Paint IMG_1125.JPG
    Reply  Wed Jul 27 23:52:18 2022, Koji, General, General, OMC #002 Cable bracket replacement (1) IMG_1126.JPGIMG_1135.JPGIMG_1127.JPGIMG_1129.JPGIMG_1130.JPG
    Reply  Thu Jul 28 00:28:15 2022, Koji, General, General, OMC #002 Cable bracket replacement (2)  IMG_1132.JPGIMG_1133.JPGIMG_1136.JPG
    Reply  Thu Jul 28 00:46:47 2022, Koji, General, General, Subject: OMC #002 Cable bracket replacement (3) IMG_1137.JPGIMG_1148.JPGIMG_1138.JPG
    Reply  Wed Aug 10 18:42:27 2022, Koji, General, General, OMC #002 Cable bracket replacement (4) PXL_20220809_235457354.jpgPXL_20220811_011910569.jpgPXL_20220811_013746139.jpg
       Reply  Thu Aug 11 15:24:57 2022, Koji, General, General, OMC #002 Cable bracket replacement (5) 
    Reply  Mon Aug 15 21:31:56 2022, Koji, General, General, OMC #002 Cable bracket replacement (6)  IMG_1155.JPGIMG_1149.JPGIMG_1150.JPG
    Reply  Mon Aug 15 22:06:18 2022, Koji, General, General, OMC #002 new cable tie installed IMG_1929.JPGIMG_1930.JPG
    Reply  Mon Aug 15 22:43:35 2022, Koji, General, General, OMC #002 Delamination repair Part1 (1) IMG_1926.JPGPXL_20220816_011346581.jpg
       Reply  Mon Aug 15 22:49:03 2022, Koji, General, General, OMC #002 Delamination repair Part1 (2) 7x
          Reply  Wed Aug 24 02:51:23 2022, Koji, General, General, OMC #002 Delamination repair Part1 (3) 8x
    Reply  Wed Aug 24 02:53:46 2022, Koji, General, General, OMC #002 Delamination repair Part2 (1) IMG_1168.JPGIMG_1169.JPGIMG_1170.JPGIMG_1171.JPGIMG_1175.JPG
       Reply  Wed Aug 24 03:20:59 2022, Koji, General, General, OMC #002 Delamination repair Part2 (2) 11x
          Reply  Wed Aug 24 03:26:43 2022, Koji, General, General, OMC #002 Delamination repair Part2 (3) 8x
    Reply  Wed Aug 24 02:57:43 2022, Koji, General, General, EP30-2 bonding setup IMG_1178.JPGIMG_1179.JPGIMG_1180.JPG
    Reply  Wed Aug 24 11:29:47 2022, Koji, General, General, OMC #002 ready for shipment IMG_1207.JPGPXL_20220825_004259850.jpgPXL_20220825_004307204.jpgPXL_20220825_005423342.jpgPXL_20220825_005549985.jpg
    Reply  Thu Aug 25 14:22:08 2022, Koji, General, General, LLO OMC #001 Ballast Mass investigation DSCN0917.JPGDSCN0922.JPGP6108705.JPGP6108707.JPGP6108706.JPG
       Reply  Thu Aug 25 20:05:00 2022, Koji, General, General, LLO OMC #001 Ballast Mass investigation balance_mass_config_LLO.pdf
    Reply  Fri Aug 26 22:29:02 2022, Koji, General, General, Tool Shipping Prep PXL_20220831_025623318.jpgPXL_20220831_024518032.jpgPXL_20220831_030234581.jpg
Message ID: 422     Entry time: Fri Jul 22 00:31:17 2022     In reply to: 415
Author: Koji 
Type: General 
Category: General 
Subject: OMC #002 backscatter measurement 

Measure the power ratio between the forward-propagating and reverse-propagating beams.

  1. Place a small deflecting mirror at the transmission.
  2. Place a flat mirror at the deflected transmission. When the alignment of this mirror is adjusted to retroreflect this beam, the DC of the cavity reflection PD increases, and also the CCD shows spurious fringes.
  3. This condition allows us to locate the power meter at the reverse-propagating spot of the transmission (Attachment 1)
  4. Place a black glass beam dump for the main (bright) transmission (Attachment 2)
  5. Now the power meter is receiving the counter-propagating beam. Turn off the room light and place an anodized Al baffle as shown in Attachment 2. Move the baffle to block only the counter-propagating. Move the baffle out. => Record the power meter reading with/without the baffle in the counter-propagating path. The difference is the power of the reverse-propagating beam.
  6. Now measure the power of the reflected main transmission. This tells us the power ratio between the foward- and back-propagating beams.
  7. Remove the small deflecting mirror and measure the power of the main transmission.
  8. Now the back-propagating power can be estimated from 6 and 7. The same amount is going back to the IFO path.
  9. The reflectivity can be calculated from the 7 and the transmission

- To increase the incident laser power, NPRO Current ADJ was set to be 0 (increased from -50)

- 1st:  Without the baffle 0.373 +/- 0.001 uW / With the baffle 0.318 +/- 0.001 uW
- 2nd: Without the baffle 0.370 +/- 0.001 uW / With the baffle 0.318 +/- 0.001 uW
- 3rd: Without the baffle 0.370 +/- 0.001 uW / With the baffle 0.317 +/- 0.001 uW

==> 53.3 +/- 0.6 nW

- The main transmission was 84.0mW
==> Backpropagation ratio was 0.634+/-0.007 ppm

- Direct measurement of the OMC was  after BS 96.6mW
==> Backpropagation power from the cavity: 61.3 +/- 0.7 nW

- Cavity transmission for the matched beam is Tcav RinputBS = 0.963
==> Incident resonant TEM00 power 100.3mW

- Reflection 61.3+/-0.7 nW x RinputBS = 60.8+/-0.7 nW
-> The effective reflectivity for the mode-matched resonant TEM00 beam incident on the OMC (1st steering mirror) is 0.606+/-0.007 ppm

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