The geoCARB sensor uses a 4-channel push broom slit-scan infrared imaging grating spectrometer to measure the absorption spectra of sunlight reflected from the ground in narrow wavelength regions. The instrument is designed for flight at geostationary orbit to provide mapping of greenhouse gases over continental scales, several times per day, with a spatial resolution of a few kilometers. The sensor provides multiple daily maps of column-averaged mixing ratios of CO2, CH4, and CO over the regions of interest, which enables flux determination at unprecedented time, space, and accuracy scales. The geoCARB sensor development is based on our experience in successful implementation of advanced space deployed optical instruments for remote sensing. A few recent examples include the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on the geostationary Solar Dynamics Observatory (SDO), the Space Based Infrared System (SBIRS GEO-1) and the Interface Region Imaging Spectrograph (IRIS), along with sensors under development, the Near Infared camera (NIRCam) for James Webb (JWST), and the Global Lightning Mapper (GLM) and Solar UltraViolet Imager (SUVI) for the GOES-R series. The Tropospheric Infrared Mapping Spectrometer (TIMS), developed in part through the NASA Instrument Incubator Program (IIP), provides an important part of the strong technological foundation for geoCARB. The paper discusses subsystem heritage and technology readiness levels for these subsystems. The system level flight technology readiness and methods used to determine this level are presented along with plans to enhance the level.
The NIRCam instrument on the James Webb Space Telescope (JWST) will provide a coronagraphic
imaging capability to search for extrasolar planets in the 2 - 5 microns wavelength range. This capability is
realized by a set of Lyot pupil stops with patterns matching the occulting mask located in the JWST
intermediate focal plane in the NIRCam optical system. The complex patterns with transparent apertures
are made by photolithographic process using a metal coating in the opaque region. The optical density
needs to be high for the opaque region, and transmission needs to be high at the aperture. In addition, the
Lyot stop needs to operate under cryogenic conditions. We will report on the Lyot stop design, fabrication
and testing in this paper.
The NIRCam instrument on the James Webb Space Telescope will have a Lyot coronagraph for high contrast imaging of
extrasolar planets and circumstellar disks at λ=2 - 5 μm. Half-tone patterns are used to create graded-transmission image
plane masks. These are generated using electron beam lithography and reactive ion etching of a metal layer on an antireflection
coated sapphire substrate. We report here on the manufacture and evaluation of the flight occulters.
The Bandpass Filters in the NIRCam instrument are required to have high throughput in bandpass spectral region and excellent
out-of-band blocking over the entire region of detector spectral response. The high throughput is needed for the instrument to have high sensitivity for detecting distant galaxies, and the out-of-band
blocking is needed for accurate calibration on James Webb Space Telescope. The operating temperature of the instrument is at cryogenic temperature from 32 Kelvin to 39.5 Kelvin. We have performed spectral measurement of NIRCam bandpass filters at cryogenic temperature after three cryo-to-ambient cycles. We will report the experiment and results in this paper. This work was performed and funded by NASA Goddard Space Flight Center under Prime Contract NAS5-02105.
The NIRCam instrument on the James Webb Space Telescope will provide coronagraphic imaging from λ =1-5 μm of
high contrast sources such as extrasolar planets and circumstellar disks. A Lyot coronagraph with a variety of circular
and wedge-shaped occulting masks and matching Lyot pupil stops will be implemented. The occulters approximate
grayscale transmission profiles using halftone binary patterns comprising wavelength-sized metal dots on anti-reflection
coated sapphire substrates. The mask patterns are being created in the Micro Devices Laboratory at the Jet Propulsion
Laboratory using electron beam lithography. Samples of these occulters have been successfully evaluated in a
coronagraphic testbed. In a separate process, the complex apertures that form the Lyot stops will be deposited onto
optical wedges. The NIRCam coronagraph flight components are expected to be completed this year.
The near-infrared camera (NIRCam) on the James Webb Space Telescope (JWST) will incorporate 2 identical
grisms in each of its 2 long wavelength channels. These transmission gratings have been added to assist with
the coarse phasing of the JWST telescope, but they will also be used for slitless wide-field scientific observations
over selectable regions of the λ = 2.4 − 5.0 μm wavelength range at spectroscopic resolution R ≡ λ/δλ ≃ 2000.
We describe the grism design details and their expected performance in NIRCam. The grisms will provide point-source
continuum sensitivity of approximately AB = 23 mag in 10,000 s exposures with S/N = 5 when binned
to R = 1000. This is approximately a factor of 3 worse than expected for the JWST NIRSpec instrument, but
the NIRCam grisms provide better spatial resolution, better spectrophotometric precision, and complete field
coverage. The grisms will be especially useful for high precision spectrophotometric observations of transiting
exoplanets. We expect that R = 500 spectra of the primary transits and secondary eclipses of Jupiter-sized
exoplanets can be acquired at moderate or high signal-to-noise for stars as faint as M = 10 − 12 mag in 1000 s of
integration time, and even bright stars (V = 5 mag) should be observable without saturation. We also discuss
briefly how these observations will open up new areas of exoplanet science and suggest other unique scientific
applications of the grisms.
The Dichroic Beam Splitter (DBS) in the NIRCam instrument is required to have small reflected wavefront error and
high throughput in order for the instrument to view the images of first light in the Universe in the James Webb Space
Telescope (JWST). The operating temperature of the instrument is from 32 Kelvin to 39.5 Kelvin. We have performed
NIRCam prototype DBS (fabricated by JDS Uniphase) spectral and reflected wavefront error measurements at cryogenic
temperatures. We report the experiment and the results in this paper.
The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) is one of the four science instruments to be installed into the Integrated Science Instrument Module (ISIM) on JWST. NIRCam's requirements include operation at 37 Kelvin to produce high-resolution images in two wave bands encompassing the range from 0.6 microns to 5 microns. In addition, NIRCam is to be used as a metrology instrument during the JWST observatory commissioning on orbit, during the precise alignment of the observatory's multiple-segment primary mirror. This paper will present the optical analyses performed in the development of the NIRCam optical system. The Compound Reflectance concept to specify coating on optics for ghost image reduction is introduced in this paper.
A multiple channel optical modulator provides a means of parallel information processing and enables fast laser printing. We have studied a multiple channel optical modulator utilizing total internal reflection (TIR) and the electro- optical properties of LiTaO<SUB>3</SUB> crystals. We characterized the multichannel TIR modulator by illuminating it separately with a source of a single mode coherent radiation (a Ti:Sapphire laser), and with a source of multimode radiation (a laser diode). The best contrast ratio (on/off intensity ratio) is 100:1, and a contrast ratio of 20:1 is achieved at a driving voltage as low as 60 V. No significant cross-talk has been observed at a modulation frequency of 10 Hz. We found that the response of the modulator is very strongly influenced by the spatial coherence of the illumination source. We also found the presence of a photorefractive effect induced by the high power density of the impinging light beam. This photorefractive effect is not permanent, and can be recovered if the laser illumination is removed for a period of time.