This work investigates intermediate materials deposited between silver (Ag) thin-film mirrors and an aluminum oxide (AlO_x) barrier overlayer and compares the effects on mirror durability to environmental stresses. Physical vapor deposition of various fluorides, oxides, and nitrides in combination with AlO_x by atomic layer deposition (ALD) is used to develop several coating recipes. Ag-AlO_x samples with different intermediate materials undergo aggressive high-temperature (80°C), high-humidity (80%) (HTHH) testing for 10 days. Reflectivity of mirror samples is measured before and after HTHH testing, and image processing techniques are used to analyze the specular surface of the samples after HTHH testing. Among the seven intermediate materials used in this work, TiN, MgAl₂O₄, NiO, and Al₂O₃ intermediate layers offer more robust protection against chemical corrosion and moisture when compared with samples with no intermediate layer. In addition, results show that the performance of the ALD-AlO_x barrier overlayer depends significantly on the ALD-growth process temperature. Because higher durability is observed in samples with less transparent TiN and NiO layers, we propose a figure of merit based on post-HTHH testing reflectivity change and specular reflective mirror surface area remaining after HTHH testing to judge overall barrier performance.

The James Webb Space Telescope near-infrared camera (JWST NIRCam) has two 2.′2×2.′2 fields of view that can be observed with either imaging or spectroscopic modes. Either of two R∼1500 grisms with orthogonal dispersion directions can be used for slitless spectroscopy over λ=2.4 to 5.0  μm in each module, and shorter wavelength observations of the same fields can be obtained simultaneously. We describe the design drivers and parameters of the grisms and present the latest predicted spectroscopic sensitivities, saturation limits, resolving powers, and wavelength coverage values. Simultaneous short wavelength (0.6 to 2.3  μm) imaging observations of the 2.4 to 5.0  μm spectroscopic field can be performed in one of several different filter bands, either infocus or defocused via weak lenses internal to the NIRCam. The grisms are available for single-object time-series spectroscopy and wide-field multiobject slitless spectroscopy modes in the first cycle of JWST observations. We present and discuss operational considerations including subarray sizes and data volume limits. Potential scientific uses of the grisms are illustrated with simulated observations of deep extragalactic fields, dark clouds, and transiting exoplanets. Information needed to plan observations using these spectroscopic modes is also provided.

The integral field spectrograph, spectrometer for infrared faint field imaging (SPIFFI), has complex line profile shapes that vary with wavelength and pixel scale, the origins of which have been sought since the instrument construction. SPIFFI is currently operational as part of SINFONI at the Very Large Telescope (VLT) and will be upgraded and incorporated into the VLT instrument enhanced resolution imager and spectrograph (ERIS). We conducted an investigation of the line profiles based on the measurements we could take with the instrument calibration unit, as well as laboratory measurements of spare SPIFFI optical components. Cryogenic measurements of a spare SPIFFI diffraction grating showed significant periodic deformation. These measurements match the cryogenic deformation expected from bimetallic bending stress based on a finite element analysis of the lightweighted grating blank. The periodic deformation of the grating surface gives rise to satellite peaks in the diffraction pattern of the grating. An optical simulation including the cryogenic grating deformation reproduces the behavior of the SPIFFI line profiles with both wavelength and pixel scale as measured with the instrument calibration unit. The conclusion is that cryogenic deformation of the diffraction gratings is responsible for the nonideal line profiles, and that the diffraction gratings should be replaced during the upgrade for optimal instrument performance.

The astronomical community continues to be interested in suitable programmable slit masks for use in multiobject spectrometers (MOSs) on space missions. There have been ground-based MOS utilizing digital micromirror devices (DMDs), and they have proven to be highly accurate and reliable instruments. This paper summarizes the results of a continuing study to investigate the performance of DMDs under conditions associated with space deployment. This includes the response of DMDs to accelerated heavy-ion radiation, to the vibration and mechanical shock loads associated with launch, and the operability of DMD under cryogenic temperatures. The optical contrast ratio and a study of the long-term reflectance of a bare device have also been investigated. The results of the radiation testing demonstrate that DMDs in orbit would experience negligible heavy-ion-induced single event upset (SEU) rate burden; we predict an SEU rate of 5.6  micromirrors/24  h. Vibration and mechanical shock testing was performed according to the NASA General Environmental Verification Standard; there were no failed mirrors in the devices tested. The results of low temperature testing suggest that DMDs are not affected by the thermal load and operate smoothly at temperatures at least as low as 78 K. The reflectivity of a bare DMD did not measurably change even after being exposed to ambient conditions over a period of 13 months even. The measured contrast ratio (“on state” versus “off state” of the DMD micromirrors) was greater than 6000∶1 when illuminated with an f/4 optical beam. Overall DMDs are extremely robust and promise to provide a reliable alternative to microshutter arrays to be used in space as remotely programmable slit masks for MOS design.

Directly deposited optical-blocking filters (DD OBFs) have the potential to improve filter performance and lower risk and cost for future x-ray imaging spectroscopy missions. However, they have not been fully characterized on high-performance charge coupled devices (CCDs). This paper reports the results of DD OBFs processed on high-performance photon-counting CCDs. It is found that CCD performance is not degraded by deposition of such filters. X-ray and optical transmission through the OBF is characterized and found to match theoretical expectation. Light-leaks through pinholes and the side and back surfaces are found to lower the optical extinction ratio; various coating processes are developed to resolve these issues.

Exciting concepts are under development for flagship, probe class, explorer class, and suborbital class NASA missions in the ultraviolet/optical spectral range. These missions will depend on high-performance silicon detector arrays being delivered affordably and in high numbers. To that end, we have advanced delta-doping technology to high-throughput and high-yield wafer-scale processing, encompassing a multitude of state-of-the-art silicon-based detector formats and designs. We have embarked on a number of field observations, instrument integrations, and independent evaluations of delta-doped arrays. We present recent data and innovations from JPL’s Advanced Detectors and Systems Program, including two-dimensional doping technology, JPL’s end-to-end postfabrication processing of high-performance UV/optical/NIR arrays and advanced coatings for detectors. While this paper is primarily intended to provide an overview of past work, developments are identified and discussed throughout. Additionally, we present examples of past, in-progress, and planned observations and deployments of delta-doped arrays.

We propose and apply two methods to estimate pupil plane phase discontinuities for two realistic scenarios on the very large telescope (VLT) and Keck. The methods use both phase diversity and a form of image sharpening. For the case of VLT, we simulate the “low wind effect” (LWE) that is responsible for focal plane errors in the spectro-polarimetric high contrast exoplanet research (SPHERE) system in low wind and good seeing conditions. We successfully estimate the simulated LWE using both methods and show that they are complimentary to one another. We also demonstrate that single image phase diversity (also known as phase retrieval with diversity) is also capable of estimating the simulated LWE when using the natural defocus on the SPHERE/differential tip tilt sensor (DTTS) imager. We demonstrate that phase diversity can estimate the LWE to within 30-nm root mean square wavefront error (RMS WFE), which is within the allowable tolerances to achieve a target SPHERE contrast of 10−6. Finally, we simulate 153-nm RMS of piston errors on the mirror segments of Keck and produce NIRC2 images subject to these effects. We show that a single, diverse image with 1.5 waves (peak-to-valley) of focus can be used to estimate this error to within 29-nm RMS WFE, and a perfect correction of our estimation would increase the Strehl ratio of an NIRC2 image by 12%.