NIRSpec DQE Project
April 21, 2005
SPACE
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INSTITUTE
JAMES WEBB
SPACE TELESCOPE
Background
• NIRSpec Project Office at GSFC requested the IDTL
to measure DQE at one wavelength in the M-band.
• IDTL accepted request and plans to make
measurement in summer 2005.
April 21, 2005
TIPS Presentation
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JAMES WEBB
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Definitions: QE
• Quantum Efficiency (QE) is a measure of
photogenerated charge as a fraction of incident
photon flux. It can appear to be greater than 1 in
devices with charge gain, i.e. photomultiplier tubes
(g~106).
QE = gh
where h is the probability that an incident photon
produced charge that was measured.
April 21, 2005
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Definitions: DQE
• Detective Quantum Efficiency (DQE) is a measure of
sensitivity. It cannot exceed 1. In the shot noise
limited case, it is a measure of photogenerated
events as a fraction of incident photon flux.
Ï ( S / N ) measured ¸
DQE = Ì
˝
Ó ( S / N ) shot ˛
April 21, 2005
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JAMES WEBB
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Definitions: DQE
hFt
Ï
Ô
2
h
Ft
+
n
Ô
r + idark t
DQE = Ì
Ft
Ô
ÔÓ
Ft
April 21, 2005
TIPS Presentation
2
¸
Ô
Ô
shot noise limited
æ
ææææ
æÆh.
˝
Ô
Ô˛
5
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When DQE=QE
• For long wavelengths, i.e. l~ lcutoff, charge gain will
be nearly 1. In this case, QE=DQE=h.
April 21, 2005
TIPS Presentation
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NIRSpec DQE Project Goals
1.
2.
3.
4.
Measure DQE at one wavelength near 5 mm for
one NIRSpec prototype detector.
Measure DQE at all wavelengths between 0.4 to
5.5 mm for one NIRSpec prototype detector.
Perform IDTL full-suite testing on one NIRSpec
prototype detector.
Train STScI personnel in detector testing, data
analysis, and lab procedures.
April 21, 2005
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Plan
1.
2.
3.
4.
Measure gain (e-/ADU) using photon transfer
experiment.
Measure DQE by obtaining stacks of flats looking
at calibrated cool blackbody with M-band filter in
the beam.
Repeat #2 using uncalibrated hot blackbody,
calibrated diode, monochromator, integrating
sphere, and order-sorting cutoff filters.
Perform remaining IDTL tests, i.e. dark current,
read noise, persistence, etc.
April 21, 2005
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Photon Transfer Experiment
• Goal is to get conversion from ADU to electrons
• Obtain stack of images at various exposure times
under constant flux. Compute median variance for
each exposure time.
s
2
ADU
s r2,e-
hFt
1 Ê hFt ˆ
1
2
2
= 2 +
= Á
˜ + s r , ADU = S ADU + s r , ADU .
G
G
GË G ¯
G
April 21, 2005
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Photon Transfer Example
April 21, 2005
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QE Example
charge gain neglected
April 21, 2005
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Spectral Flat Fields near 1 mm
fringing
12
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Si PIN QE versus Wavelength
100%
90%
140 K
160 K
180 K
200 K
80%
70%
QE
60%
50%
40%
30%
20%
10%
0%
800
850
900
950
1000
1050
1100
Wavelength (nm)
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IDTL Test System
Leach II Controller Electronics
Dewar
(6Kx6K capacity)
Entrance
Window
Vacuum Hose
He Lines
April 21, 2005
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Experiment Setup #1
420K BB
Source
Pinhole
camera
April 21, 2005
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Experiment Setup #2
Integrating
Sphere
T
MC
e
diod
April 21, 2005
Pinhole
diode
chrom.
Source
MCT
Mono-
1000K BB
camera
TIPS Presentation
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Calibrated Blackbody Source
•
•
•
•
•
Mikron M340
T=253°K-423 °K +/-0.1°K
NIST traceable
Stabilizes in ~10 min.
Source temperature
controlled by PID controller
which displays
temperature in a digital
readout.
• Controlled/read by RS232.
April 21, 2005
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Calibrated MCT Diode
•
•
•
•
•
•
•
•
Sciencetech, Inc.
Detector Type: HgCdTe Photoconductor
Active Area: 1.0 mm x 1.0 mm
Spectral range: 2.0 –15.0+ _m; pk @ 13 um
Detectivity (D*pk): 4.0 x 10^10 cm-Hz^1/2/W, min
Dewar Hold Time: 12 hours minimum with liquid N2
Field of View: 60o nominal
Responsivity (pk), 10^6 V/W HI ; 10^4 V/W LO
April 21, 2005
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Estimated Fluxes
• Assumes 50 mm pinhole diameter
• 2400 ph/s/pixel/M-band at 423 °K
• 91 ph/s/pixel/M-band at 293 °K
April 21, 2005
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Schedule
April 21, 2005
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Personnel
•
•
•
•
•
Don Figer
Lance Simms (SLAC)
Mike Regan
Ernie Morse
Sylvia Baggett
April 21, 2005
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Current IDTL Projects
1.
2.
3.
4.
5.
LSST Detector Testing Project. Goal: Test performance of
two SiPIN detectors for LSST. PI: Figer. Deadline: August
2005. Status: First part completed. Second part to be tested
in May.
SNAP Detector Testing Project. Goal: Test performance of
three MCT detectors for SNAP. PI: Figer. Deadline: October
2005. Status: First part completed.
JDEM Detector Testing Project. Goal: Test performance of
one MCT detector for JDEM. PI: Figer. Deadline: October
2005.
JWST NIRSpec DQE Testing Project. Goal: Measure DQE.
PI: Figer. Deadline: September 2005.
WHIRC. Goal: Integrate MONSOON Detector Controller into
WHIRC instrument. PI: Meixner.
April 21, 2005
TIPS Presentation
22