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 (0.6-2.3m) and long (2.4-5) sections

– Nyquist sampling at 2 and 4m– 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

• Each module has two channels (0.6 to 2.3 m and 2.4 to 5 m)

– 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”/pixLW: 0.064”/pix

Long wavelength channelShort wavelength channel

Mo

du

le A

Mo

du

le B

2.2’

Focus and alignment

mechanism

Coronagraphocculting masks

First fold mirror

Collimator lens group

Dichroic beamsplitter

Long wave filter wheel assembly

Long wave camera lens

group

Long wave focal plane housing

Short wave filter wheel assembly

Short wave camera lens group

Short wave fold mirror

Pupil imaging lens assembly

Short wave focal plane housing

Light from OTE

Pick-off Mirror

Module A

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

• Tests were generally very successful– Operated with the flight software over eight days with no crashes or major problems– Wavefront sensing components were 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.

“First Light”Fuzzy because of chamber vibrations, tests were done with “pulsed light”

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.

(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.

Detector Latency

(a) (b)(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.