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 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 James Webb Space Telescope (JWST) is a space-based, infrared observatory designed to study the early stages of
galaxy formation in the Universe. It is currently scheduled to be launched in 2013 and will go into orbit about the
second Lagrange point of the Sun-Earth system and passively cooled to 30-50 K to enable astronomical observations
from 0.6 to 28 μm. The JWST observatory consists of three primary elements: the spacecraft, the optical telescope
element (OTE) and the integrated science instrument module (ISIM). The ISIM Element primarily consists of a
mechanical metering structure, three science instruments and a fine guidance sensor with significant scientific capability.
One of the critical opto-mechanical alignments for mission success is the co-registration of the OTE exit pupil with the
entrance pupils of the ISIM instruments. To verify that the ISIM Element will be properly aligned with the nominal
OTE exit pupil when the two elements come together, we have developed a cryogenic pupil measurement test
architecture to measure three of the most critical pupil degrees-of-freedom during optical testing of the ISIM Element.
The pupil measurement scheme makes use of: specularly reflective pupil alignment references located inside of the
JWST instruments; ground support equipment that contains a pupil imaging module; an OTE simulator; and pupil
viewing channels in two of the JWST flight instruments. Current modeling and analysis activities indicate this
measurement approach will be able to verify pupil shear to an accuracy of 0.5-1%.
The expected stable point spread function, wide field of view, and sensitivity of the NIRCam instrument on the James
Webb Space Telescope (JWST) will allow a simple, classical Lyot coronagraph to detect warm Jovian-mass companions
orbiting young stars within 150 pc as well as cool Jupiters around the nearest low-mass stars. The coronagraph can also
be used to study protostellar and debris disks. At λ = 4.5 μm, where young planets are particularly bright relative to their
stars, and at separations beyond ~0.5 arcseconds, the low space background gives JWST significant advantages over
ground-based telescopes equipped with adaptive optics. We discuss the scientific capabilities of the NIRCam
coronagraph, describe the technical features of the instrument, and present end-to-end simulations of coronagraphic
observations of planets and circumstellar disks.
A new technique for creating optical masks with a transmittance that varies spatially according to an arbitrary usersupplied
equation is discussed. Initial fabrication and testing demonstrates the viability of the technique, as well as
showing the effect of various deposition parameters in the resulting product. The test data are compared to both
simulated and ideal results. The application of this technique to the creation of a coronagraphic filter with strong
central attenuation and minimal edge diffraction is also discussed.
Smithsonian Astrophysical Observatory (SAO) has set up a program to study coronagraphic techniques. The program consists of the development of new fabrication methods of occulter masks, characterization of the manufactured masks, and application of the masks to study speckle reduction technique. Our occulter mask fabrication development utilizes a focused ion beam system to directly shape mask profiles from absorber material. Initial milling trials show that we can shape nearly Gaussian-shaped mask profiles. Part of this development is the characterization of absorber materials, poly(methyl methacrylate) doped with light-stable chromophores. For the characterization of the masks we have built a mask scanner enabling us to scan the transmission function of occulter masks. The real mask transmission profile is retrieved applying the maximum entropy method to deconvolve the mask transmission function from the beam profile of the test laser. Finally, our test bed for studying coronagraphic techniques is nearing completion. The optical setup is currently configured as a classical coronagraph and can easily be re-configured for studying speckle reduction techniques. The development of the test bed control software is under way. This paper we will give an update of the status of the individual program elements.
SAO has set up a testbed to study coronagraphic techniques, starting with Labeyrie's multi-step speckle reduction technique. This technique expands the general concept of a coronagraph by incorporating a speckle corrector (phase and/or amplitude) in combination with a second occulter for speckle light suppression. Here we are describing the initial testbed configuration. In addition, the testbed will be used to test a new approach of the phase diversity method to retrieve the speckle phase and amplitude. This method requires measurements of the speckle pattern in the focal plane and slightly out-of-focus. Then we will calculate a phase of the wave from which we can derive a correction function for the speckle corrector. Furthermore we report results from a parallel program which studies new manufacturing methods of soft-edge occulter masks. Masks were manufactured using the spherical caps method. Since the results were not satisfying we also investigated the method of ion beam milling of masks. Here we will present the outline of this method. Masks manufactured with both methods will be fully characterized in our mask tester before their use in the testbed.
The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) is one of the four science instruments installed into the Integrated Science Instrument Module (ISIM) on JWST intended to conduct scientific observations over a five year mission lifetime. NIRCam's requirements include operation at 37 kelvins (K) to produce high resolution images in two wave bands encompassing the range from 0.6 microns to 5 microns. In addition NIRCam is used as a metrology instrument during the JWST observatory commissioning on orbit, during the initial and subsequent precision alignments of the observatory's multiple-segment 6.3 meter primary mirror. This paper describes some preliminary performance results of prototype coronagraph masks.
The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) is one of the four science instruments installed into the Integrated Science Instrument Module (ISIM) on JWST intended to conduct scientific observations over a five-year mission lifetime. NIRCam's requirements include operation at 37 kelvins to produce high resolution images in two wave bands encompassing the range from 0.6 microns to 5 microns. In addition NIRCam is used as a metrology instrument during the JWST observatory commissioning on orbit, during the initial and subsequent precision alignments of the observatory's multiple-segment 6.3 meter primary mirror. JWST is scheduled for launch and deployment in 2012. This paper is an overview of the NIRCam instrument's Optical Calibration Sources (Flat Field and Point Source). It will discuss the source requirements and will explain the optical and electronic technology developed to fulfill their mission requirements.