NIRCam ETU Testing at
LMATC, Palo Alto
Kailash C. Sahu
What’s NIRCam?
• NIRCam is the near-infrared camera (0.6-5
microns) for JWST
– Dichroic used to split range into short (0.62.3mm) and long (2.4-5m) sections
– Nyquist sampling at 2 and 4mm
– Coronagraphic capability for both short and
long wavelengths
– Low-resolution spectroscopic capability in
the LW channel.
• NIRCam is the wavefront sensor
– Must be fully redundant
2 Channels Per Module
– 7 wide band filters (4 SW,
3 LW) for deep surveys
– Survey efficiency is
increased by observing
the same field at long and
short wavelength
simultaneously
• Pixel scale:
SW: 0.032”/pix
LW: 0.064”/pix
Module B
• Each module has two
channels (0.6 to 2.3 mm
and 2.4 to 5 mm)
Module A
Short wavelength channel
2.2’
Long wavelength channel
Light from OTE
Collimator
lens group
Short wave camera
lens group
First fold
Short wave
mirror
fold mirror
Pupil imaging lens
assembly
Dichroic
beamsplitter
Coronagraph
occulting masks
Short wave filter
wheel assembly
Pick-off Mirror
Focus and
alignment
mechanism
Long wave filter
wheel assembly
Short wave focal
plane housing
Module A
Long wave
camera lens
group
Long wave focal
plane housing
NIRCam ETU/WFS Testing
• 1-9 April at LMATC (Lockheed Martin
Advanced Techonology Center), Palo
Alto
• First ~3 days (after the “Red Chamber”
attained operating temperature of ~38K)
spent on SCA/Assembly testing, rest on
WFS testing (only with the SW channel).
• People from STScI:
• Massimo Robberto,
• Elizabeth Barker,
• Kailash Sahu (WIT).
• George Hartig,
• Erin Elliot (TEL)
NIRCam ETU/WFS Testing
“First Light”
• Tests were generally very successful
– Operated with the flight software over eight
Fuzzy because of chamber days with no crashes or major problems
vibrations, tests were done – Wavefront sensing components were
with “pulsed light”
demonstrated to work in the NIRCam pupil
Main problems:
- Transfer of FITS files often needed manual
intervention.
- PIL (Pupil Imaging Lens) had some
alignment problems.
Structure in this image is due to the known
poor alignment of the OMA and ETU at this
early stage.
Weak Lens Images
The shapes are very close to predicted images.
Ghosts are due to reflections in the OMA optics,
not NIRCam
DHS Spectra
Spectra are at the correct angle.
Known emission line in the super
continuum source being used for
illumination.
A spectrum extracted from the
previous image. The “notches” in the
filter used in series with the DHS are
apparent.
Flat Fields from Internal Red
Chamber Lamps
Detector Linearity from Chamber
Lamp
Data
Sample ramps from
independent exposures
Black: Without linearity correction
Blue: After linearity correction
These data are the first chance we had to check linearity with ASIC + SCA.
Overall linearity is good (better than 5%) and is dominated by SCA, not ASIC.
Some systematic effects at “low” count rates need to be investigated further.
Detector Latency
(a)
(b)
(a) Over-saturated point source image taken during ETU testing.
Estimated counts (from the ghost): 650,000 to 1 million DN.
(b) Exposure taken immediately after (a).
Counts at the peak of the point source: ~650 DN (< 0.1%)
(c) Exposure taken ~4 minutes later.
Peak counts: ~80 DN.
(c)
SUMMARY
• Initial SCA and WFS testing results are very encouraging.
• The software operated relatively smoothly, but problems
were identified which will be rectified in time for FM testing.
• Participations from all the groups (GSFC, LMATC, UA and
STScI) were coherent and complimentary.
• All the ETU Test data are being archived at STScI through
SID archive.
Sample Images from the Focus
Sweeps
These are not organized in any fashion and some were taken at different
wavelengths.
PIL Image of DHS
Blue areas are due to
the missing pieces in
the DHS. Segment
gaps and the
secondary supports are
evident.