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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

OBU

OTAFPP

Calibrated PSD sensor

Heliostat flat mirrors

Natural sun light

NAOJ clean room

Entrance window

OBU

OTAFPP

Calibrated PSD sensor

Heliostat flat mirrors

Natural sun light

NAOJ clean room

Entrance window

Test configuration

NAOJ Heliostat on the roof of clean room

Sun light illuminated OTA full aperture

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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 wavelengthsEstimated photons at 1 solar light (1x1 sum)

Longest exposure without saturation

Optical path

(nm)

Gain (e/DN)

Photon count (DN) 1)

Exposure time (msec)

Difference from

prediction (%)

CCD well depth

(%) 1x1 sum (msec)

2x2 sum (msec)

CT 630.0 48 873~885 frame 65~66 42~42% 26922~28662 48 frames 124~132 40~43% SP (left)

(right) 630.2 100

22811~24284 48 frames 105~111 34~36%

388.3 505 100ms exp 105 310 182 396.9 1441~1062 1000ms exp 151~111 1084~1471 630~863 430.5 2352~2033 100ms exp 90~78 66~77 45~49 450.5 1326~1168 100ms exp 112~98 118~134 71~79 555.0 646~684 100ms exp 63~66 242~228 140~132

BFI

668.4

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1048~1110 100ms exp 54~57 149~141 86~82 517.3 183 100ms exp 53 839 505 525.0 382~404 100ms exp 87~92 409~387 228~218 557.6 391~416 100ms exp 106~113 400~376 228~221 589.6 705 100ms exp 127 219 129 630.2 580~552 100ms exp 130~124 269~283 162~165

NFI 2)

656.3

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515~507 100ms exp 135~133

303~308 180~181 Note 1) Two values are given in each data. The first value is the throughput determined from all the data points

collected in the 2004 SOT sun test. The last value is the throughput determined from the best data taken with clear sky on 2004/8/18, giving more confident values.

Note 2) NFI measurements were made for nearby continuum near the spectral line of interest. Exposure duration

would be increased when the wavelength is located inside the profile of spectral line.

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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%).

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.

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 60-25

0msec for 2x2 (all the wavelengths). Shutterless observables with 100msec works properly. Since a few 200msec shutterless observables may be saturated, alternate obs

ervables (100msec exposures at two field of view) are prepared.