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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
Natural sun light
Heliostat flat
mirrors
Calibrated
PSD sensor
Entrance
window
Sun light illuminated
OTA full aperture
NAOJ clean room
OTA
NAOJ Heliostat on the
roof of clean room
FPP
OBU
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Test configuration
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
Optical
path
CT
SP (left)
(right)
BFI

(nm)
630.0
630.2
Gain
(e/DN)
48
100
Estimated photons at 1
solar light (1x1 sum)
Photon count
Exposure
1)
(DN)
time (msec)
Difference
from
prediction
(%)
CCD
well
depth
(%)
42~42%
40~43%
34~36%
Longest exposure
without saturation
1x1 sum
2x2 sum
(msec)
(msec)
873~885
frame
65~66
26922~28662
48 frames
124~132
22811~24284
48 frames
105~111
388.3
64
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
668.4
1048~1110
100ms exp
54~57
149~141
86~82
NFI 2)
517.3
64
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
656.3
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)
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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)

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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)
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Shuttered observables have exposure time of 100-400msec for 1x1 and 60250msec 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)
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
CT data will have suitable number of photons in flight.
The expected photon level in flight is 42% of the CCD full well.
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