Estimate on SOT light level in flight with throughput measurements in SOT sun tests

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Estimate on SOT light level in flight with
throughput measurements in SOT sun tests

• T. Shimizu1, T. Tarbell2, T. Berger2, Y.
  Suematsu3, M. Kubo1,
• K. Ichimoto3, Y. Katsukawa3, M. Miyashita3,
• M. Noguchi3, M. Nakagiri3, S. Tsuneta3,
• D. Elmore4, B. Lites4 and SOT team
• 1. ISAS/JAXA, 2. LMSAL, 3. NAOJ, 4. HAO/NCAR

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• Light throughput measurement before the flight is
  very important to confirm that CCD will not be
  over-saturated in flight as well as
  signal-to-noise performance.
• Natural solar light was fed to the integrated SOT
  flight model in two sun-test opportunities.
• CCD exposures provide the number of photons
  accumulated in an exposure-duration in clean room
  test condition.
• A pinhole-PSD (position sensitive detector)
  sensor (525 nm band) was used to monitor the
  light level simultaneously, giving the absolute
  light level.
• Transmissivity of heliostat two flat mirrors plus
  clean-room entrance window glass was also
  measured as a function of wavelength.
• This throughput measurement with solar light has
  confirmed adequate light level in flight
  experimentally.

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Sun Tests
Sun light illuminated OTA full aperture
NAOJ Heliostat on the roof of clean room
Test configuration
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Pre-calibrated standard Sensor

• A pinhole-PSD (position sensitive detector)
  sensor (525 nm band) was used to monitor the
  light level simultaneously, giving the absolute
  light level.
• The PSD sensor was pre-calibrated with continuous
  monitoring the solar light level in a day long
  under a clear constant sky condition, giving what
  is the voltage for one solar light level.

Pinhole-PSD sensor
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• Summary of photon level in flight for all the
  wavelengths

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• Spectro-Polarimeter (SP)
• SP data will have suitable number of photons in
  flight.
• The continuum photon level accumulated in each
  exposure (0.1sec) is 34-40 of the CCD full well.
  
• The signal-to-noise achieved with 4.8 sec (48
  frame) accumulation is 1500 (0.07). S/N with
  3.2sec (32 frame) accumulation is 1235 (0.08).

• Broadband Filter Imagers (BFI)
• All the wavelengths are not saturated.
• G-band has the shortest exposure time (30 msec
  for half of full well).
• Ca IIH has the longest exposure time (300-500msec
  for half of full well).

• Narrowband Filter Imagers (NFI)
• Shuttered observables have exposure time of
  100-400msec for 1x1 and 60-250msec for 2x2 (all
  the wavelengths).
• Shutterless observables with 100msec works
  properly.
• Since a few 200msec shutterless observables may
  be saturated, alternate observables (100msec
  exposures at two field of view) are prepared.

• Correlation Tracker (CT)
• CT data will have suitable number of photons in
  flight.
• The expected photon level in flight is 42 of the
  CCD full well.