1 Minute of KAGRA AOS Meeting on Optical Levers
   2 [Wiki page]
   3 http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/LCGT/subgroup/AOS/Meetings#m9th
   4 This page is written by Japanese,
   5 but you can find Michimura-kun's slide and Sekiguchi-kun's
   6 simulation/calculation)
   7 
   8 --------------------------
   9 Date: Apr 27, 2012 10:00-12:00 (JST)
  10 Place: Tsubono Lab + EVO
  11 Participants: T. Akutsu, Y. Aso, R. DeSalvo, U. Iwasaki, Y. Saito,
  12 E. Majorana, L. Naticchioni, Y.Michimura, T. Sekiguchi, R. Takahashi,
  13 and M. Ando (EVO)
  14 [Most of the minute by Michimura]
  15 
  16 (1) THE FUNCTION OF OPLEVS
  17  - sensing angular motion of mirrors for damping the resonant peaks
  18 (local control)
  19  - angular drift monitor for mirrors and optical benches
  20  - coil balancing
  21 
  22 
  23 (2) WHERE DO OPLEVS GO?
  24  - TMs
  25   for iKAGRA: viewports above and below, lever length ~ 1.5 m, incident
  26 angle ~ 45 deg
  27   for bKAGRA: viewports at AO chamber, use pick off mirror (or using a
  28 crank position where vacuum tube radius would change), lever length ~ 30
  29 m, incident angle ~ 1 deg
  30 
  31  - BS
  32   one viewport below, lever length ~ 1m, incident angle few deg
  33 
  34  - RC mirrors
  35   viewports above and below, lever length ~ 1.5 m, incident angle ~ 45 deg
  36 
  37  - MC mirrors, MMT mirrors, etc.
  38   same as RC mirrors? (TBD)
  39 
  40  - optical benches
  41   viewport below? (TBD)
  42 
  43 
  44 (3) DESIGN
  45  - folding or 2-QPDs?
  46   OpLevs are for the angular sensing, not the longitudinal sensing
  47   so, let's set the folding method as a default
  48 
  49 
  50 (4) REQUIREMENTS
  51  - power ~ 5 mW, RIN ~ 1e-7 /rtHz (preliminary)
  52   are there any S-LED which satisfy this requirement?
  53 
  54  - wavelength TBD
  55   decisive factor is the life time
  56 
  57  - pointing drift
  58   smaller than 0.4 urad/h
  59   we have to care about the drift due to the temperature drift of the pylon
  60   for bKAGRA TMs, we also have to care about the relative drift between
  61 the base inside the chamber and the ground
  62 
  63  - sensing range
  64   we need two kind; low noise but small range + noisy but larger range
  65   for TMs we need ~ ± 100 mm at most (considering mirror motion ± 1
  66 mrad)
  67   for other mirrors, ~ ± 10mm at most
  68 
  69 
  70 (5) MISCS
  71  - we have to measure the reflectivity of the HR coating for OpLev light
  72  - the size of the viewports and also the holes on the optical bench
  73 must be larger than the beam size of the OpLev beam and the beam motion
  74 (10cm should be enough?)
  75  - QPDs should be rotatably mounted for pitch/yaw diagonalization
  76  - local control should be done at the higher stages of the suspention,
  77 using steep servo filters specially designed for each suspention
  78 
  79 (6) ACTION ITEMS
  80  - selection of the light source and sensors (TBD.)
  81  - design of the pylon for launcher/sensor (TBD.)
  82  - calculation of the local damping of the resonant peaks using OpLevs
  83 and other local sensors (Sekiguchi, Michimura)