Quantum Efficiency Measurements of a
NIRSpec infrared sensor in the ODL*
Peter McCullough, Project P. I.
Mike Regan, ODL Lead
Kevin Lindsay
Eddie Bergeron
Thanks to Bernie Rauscher and Don Figer, et al.
See JWST-STScI-001053 for details.
Presented to TIPS at STScI
by McCullough
Mar 15, 2007
*ODL = Operations Detector Lab at STScI and JHU
Monochromator
Optical Coupling
Lamp
Lockin and cable
for PbSe diode
Blackbody
Image of Blackbody
8
•Blackbody
•Window
•Filter
•Pinhole
•Detector
•Dewar
Simple  Predictable
R
Contours are in
counts (ADUs)
Insert Integrating Sphere to make flat fields
Flat Field
4.5 um
(Subsampled to 512x512)
White: QE=1.05
Black: QE<0.85
Bad pixels: << 1% by
number
Corners have low QE
Reference pixels visible as
black edges
Flat Field
3.9 um
(Subsampled to 512x512)
White: QE=1.05
Black: QE<0.85
Bad pixels: << 1% by
number
Corners have low QE
Reference pixels visible as
black edges
(Same caption as
previous slide, just
different wavelength).
Gain requires accurate nonlinearity correction
0.8 um photons give different
gain than 1.8 um photons.
Interpreted as due to a quantum
yield. Analysis in preparation.
2
Gain versus
wavelength
and binning
Bin factor
1
2
3
4
5
1
0
0.8
Wavelength (um)
2.7
Apparent Gain depends on
binning, due to interpixel
capacitance.
0
z
0
z
1-4z
z
0
z
0
(circuit diagram from Finger et al. 2005)
Summary
JWST-STScI-001053
• Rockwell (Teledyne) 2kx2k sensor H2RG-S010 tested in
Operations Detector Lab at STScI.
• Median QE = 95% within 5% (1 sigma) at tested wavelengths
(3.38, 3.9, 4.5 microns).
• Interpixel capacitance (IPC) is significant and blurs images
due to the 2.5% crosstalk to each of the 4 nearest-neighbor
pixels. Neglecting this crosstalk would cause the QE to be
overestimated by 2*4*2.5% = 20%. This is apparently typical
for epoxy-filled H2RG devices.
• New analysis (binning method) invented to account for IPC in
measurement of system gain; alternative to autocorrelation
method previously used. Intuitive and more resistant to EMI.
• Analysis of measurements from 0.5 to 6.0 um in preparation.