To maintain the required performance of WFIRST Coronagraph in a realistic space environment, a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem is necessary. The LOWFS/C uses a Zernike wavefront sensor (ZWFS) with the phase shifting disk combined with the starlight rejecting occulting mask. For wavefront error corrections, WFIRST LOWFS/C uses a fast steering mirror (FSM) for line-of-sight (LoS) correction, a focusing mirror for focus drift correction, and one of the two deformable mirrors (DM) for other low order wavefront error (WFE) correction. As a part of technology development and demonstration for WFIRST Coronagraph, a dedicated Occulting Mask Coronagraph (OMC) testbed has been built and commissioned. With its configuration similar to the WFIRST flight coronagraph instrument the OMC testbed consists of two coronagraph modes, Shaped Pupil Coronagraph (SPC) and Hybrid Lyot Coronagraph (HLC), a low order wavefront sensor (LOWFS), and an optical telescope assembly (OTA) simulator which can generate realistic LoS drift and jitter as well as low order wavefront error that would be induced by the WFIRST telescope’s vibration and thermal changes. In this paper, we will introduce the concept of WFIRST LOWFS/C, describe the OMC testbed, and present the testbed results of LOWFS sensor performance. We will also present our recent results from the dynamic coronagraph tests in which we have demonstrated of using LOWFS/C to maintain the coronagraph contrast with the presence of WFIRST-like line-of-sight and low order wavefront disturbances.
NASA WFIRST-AFTA mission study includes a coronagraph instrument to find and characterize exoplanets. Various types of masks could be employed to suppress the host starlight to about 10−9 level contrast over a broad spectrum to enable the coronagraph mission objectives. Such masks for high-contrast internal coronagraphic imaging require various fabrication technologies to meet a wide range of specifications, including precise shapes, micron scale island features, ultralow reflectivity regions, uniformity, wave front quality, and achromaticity. We present the approaches employed at JPL to produce pupil plane and image plane coronagraph masks by combining electron beam, deep reactive ion etching, and black silicon technologies with illustrative examples of each, highlighting milestone accomplishments from the High Contrast Imaging Testbed at JPL and from the High Contrast Imaging Lab at Princeton University.
Star light suppression technologies to find and characterize faint exoplanets include internal coronagraph instruments as well as external star shade occulters. Currently, the NASA WFIRST-AFTA mission study includes an internal coronagraph instrument to find and characterize exoplanets. Various types of masks could be employed to suppress the host star light to about 10-9 level contrast over a broad spectrum to enable the coronagraph mission objectives. Such masks for high contrast internal coronagraphic imaging require various fabrication technologies to meet a wide range of specifications, including precise shapes, micron scale island features, ultra-low reflectivity regions, uniformity, wave front quality, achromaticity, etc. We present the approaches employed at JPL to produce pupil plane and image plane coronagraph masks by combining electron beam, deep reactive ion etching, and black silicon technologies with illustrative examples of each, highlighting milestone accomplishments from the High Contrast Imaging Testbed (HCIT) at JPL and from the High Contrast Imaging Lab (HCIL) at Princeton University. We also present briefly the technologies applied to fabricate laboratory scale star shade masks.
NASA’s WFIRST-AFTA mission concept includes the first high-contrast stellar coronagraph in space. This coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. In this paper we present the plan for maturing coronagraph technology to TRL5 in 2014-2016, and the results achieved in the first 6 months of the technology development work. The specific areas that are discussed include coronagraph testbed demonstrations in static and simulated dynamic environment, design and fabrication of occulting masks and apodizers used for starlight suppression, low-order wavefront sensing and control subsystem, deformable mirrors, ultra-low-noise spectrograph detector, and data post-processing.
High contrast internal and external coronagraphic imaging requires a variety of masks depending on different architectures to suppress star light. Various fabrication technologies are required to address a wide range of needs including gradient amplitude transmission, tunable phase profiles, ultra-low reflectivity, precise small scale features, and low-chromaticity. We present the approaches employed at JPL to produce pupil plane and image plane coronagraph masks, and lab-scale external occulter type masks by various techniques including electron beam, ion beam, deep reactive ion etching, and black silicon technologies with illustrative examples of each. Further development is in progress to produce circular masks of various kinds for obscured aperture telescopes.
We report on the development of waveguide-based mixers for operation beyond 2 THz. The mixer element is a
superconducting hot-electron bolometer (HEB) fabricated on a silicon-on-insulator (SOI) substrate. Because it is beyond
the capability of conventional machining techniques to produce the fine structures required for the waveguide embedding
circuit for use at such high frequencies, we employ two lithography-based approaches to produce the waveguide circuit:
a metallic micro-plating process akin to 3-D printing and deep reactive ion etching (DRIE) silicon micromachining.
Various mixer configurations have been successfully produced using these approaches. A single-ended mixer produced
by the metal plating technique has been demonstrated with a receiver noise temperature of 970 K (DSB) at a localoscillator
frequency of 2.74 THz. A similar mixer, produced using a silicon-based micro-machining technique, has a
noise temperature of 2000 K (DSB) at 2.56 THz. In another example, we have successfully produced a waveguide RF
hybrid for operation at 2.74 THz. This is a key component in a balanced mixer, a configuration that efficiently utilizes
local oscillator power, which is scarce at these frequencies. In addition to allowing us to extend the frequency of
operation of waveguide-based receivers beyond 2 THz, these technologies we employ here are amenable to the
production of large array receivers, where numerous copies of the same circuit, precisely the same and aligned to each
other, are required.
We present test results from a compact, fast (F/1.4) imaging spectrometer system with a 33° field of view, operating in
the 450-1650 nm wavelength region with an extended response InGaAs detector array. The system incorporates a simple
two-mirror telescope and a steeply concave bilinear groove diffraction grating made with gray scale x-ray lithography
techniques. High degree of spectral and spatial uniformity (97%) is achieved.
The development of Fourier Transform (FT) spectral techniques in the soft X-ray spectral region has been advocated in
the past as a possible route to constructing a bench-top size spectral imager with high spatial and spectral resolution.
The crux of the imager is a soft X-ray interferometer. Auxiliary subsystems include a wide-band soft X-ray source,
focusing optics and detection systems. When tuned over a sufficiently large range of path delays, the interferometer will
sinusoidally modulate the source spectrum centered at the core wavelength of interest, the spectrum illuminates a target,
the reflected signal is imaged onto a CCD, and data acquired for different frames is converted to spectra in software by
using FT methods similar to those used in IR spectrometry producing spectral image per each pixel. The use of shorter
wavelengths results in dramatic increase in imaging resolution, the modulation across the beam width results in highly
efficient use of the beam spectral content, facilitating construction of a bench-top instrument. With the predicted <0.1eV
spectral and <100 nm spatial resolution, the imager would be able to map core-level shift spectra for elements such as
Carbon, which can be used as a chemical compound fingerprint and imaging intracellular structures.
We report on our progress in the development of a Fourier Transform X-ray (FTXR) interferometer. The enabling
technology is X-ray beam splitting mirrors. The mirrors are not available commercially; multi layers of quarter-wave
films (used in IR and visible) are not suitable, and several efforts by other researchers who used parallel slits met only a
very limited success. In contrast, our beam splitters use thin (about 200 nm) SiN membranes perforated with a large
number of very small holes prepared in our micro-fabrication laboratory at JPL. Precise control of surface roughness
and high planarity are needed to achieve the requisite wave coherency. The beam splitters prepared-to-date had surface
RMS and planarity better that <0.3 nm over a 0.45 mm x 1.4 mm area, meeting requirements for spectral imaging at
100eV. Efforts to improve the mirror flatness to a level required for core-level shifts of Carbon are under way.
The Princeton occulter testbed uses long-distance propagation with a diverging beam and an optimized
occulter mask to simulate the performance of external occulters for finding extrasolar planets. We present
new results from the testbed in both monochromatic and broadband light. In addition, we examine sensing
and control of occulter position using out-of-band spectral leak around the occulter and occulter position
tolerancing. These results are validated by numerical simulations of propagation through the system.
An occulter is used in conjunction with a separate telescope to suppress the light of a distant star. To
demonstrate the performance of this system, we are building an occulter experiment in the laboratory at
Princeton. This experiment will use an etched silicon mask as the occulter, with some modifications to try
to improve the performance. The occulter is illuminated by a diverging laser beam to reduce the aberrations
from the optics before the occulter. We present the progress of this experiment and expectations for future
The development of Fourier Transform (FT) spectral techniques in the soft X-ray (100eV to 500eV spectral region)
has been advocated in the past as a possible route to constructing a bench-top size spectral imager with high spatial
and spectral resolution. The crux of the imager is the soft X-ray interferometer. The auxiliary subsystems include a
soft X-ray source, focusing optics and a CCD-based detection system. When tuned over a sufficiently large range of
path delays (frames), the interferometer will sinusoidally modulate a spectrum of a wide-band X-ray source centered at
the core wavelength of interest with high resolving power. The spectrum illuminates a target, the reflected signal is
imaged onto a CCD, and data acquired for different frames is converted to spectra in software by using FT methods
similar to those used in IR spectrometry, producing spectral image per each pixel. The use of short wavelengths results
in dramatic increase in imaging resolution over that for IR. Important for future NASA missions, and unlike X-ray
Absorption Near Edge Structure (XANES) that uses intense and in monochromatic beams which only a synchrotron
can deliver, FTXR plans to use a miniature, wide bandwidth X-ray source. By modulating the beam spectrum around
the wavelength of interest, the beam energy is used much more efficiently than with gratings (when only a very small,
monochromatized portion of the radiation is used at one time) facilitating construction of a bench-top instrument. With
the predicted <0.1eV spectral and <100 nm spatial resolution, the imager would be able to map a core-level shift
spectrum for each pixel of the image for elements such as C, Si, Ca, N (Kα-lines) which can be used as a chemical
compound fingerprint and for imaging intracellular structures. For heavy elements it could provide "bonding maps"
(L and M-shell lines), enabling to study fossils of microorganisms on space missions and in returned samples to Earth.
We have initiated development of a Fourier Transform X-ray Reflection (FTXR) spectral imager based on the use of a
Mach-Zender type interferometer. The enabling technology for the interferometer is the X-ray beam splitting mirrors.
The mirrors are not available commercially; multi layers of quarter-wave films are not suitable, requiring a different
approach to beam-splitters than in the visible or IR regions. Several efforts by other researchers used parallel slits or
stripes for partial transmission, with only a very limited success. In contrast, our beam splitters are based on thin
(about 200 nm) SiN membranes perforated with a large number of very small holes, prepared using state-of-art microfabrication
techniques that have only recently become available in our laboratory at JPL. Precise control of surface
roughness and high planarity are needed to achieve the wave coherency required for high-contrast fringe forming. The
perforation design is expected to result in much greater surface flatness, facilitating greater wave coherence than for
the other techniques. We report on our progress in the fabrication of beam splitting mirrors to-date, interferometer
design, modeling, assembly, and experimental results.
The Shaped Pupil Coronagraph (SPC) is a high-contrast imaging system pioneered at Princeton for detection of extra-solar earthlike planets. It is designed to achieve 10-10 contrast at an inner working angle of 4λ/D in broadband light. A critical requirement in attaining this contrast level in practice is the ability to control wavefront phase and amplitude aberrations to at least λ/104 in rms phase and 1/1000 rms amplitude, respectively. Furthermore, this has to be maintained over a large spectral band. The High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Lab (JPL) is a state-of-the-art facility for studying such high contrast imaging systems and wavefront control methods. It consists of a vacuum chamber containing a configurable coronagraph setup with a Xinetics deformable mirror. Previously, we demonstrated 4x10-8 contrast with the SPC at HCIT in 10% broadband light. The limiting factors were subsequently identified as (1) manufacturing defects due to minimal feature size constraints on our shaped pupil masks and (2) the inefficiency of the wavefront correction algorithm we used (classical speckle nulling) to correct for these defects. In this paper, we demonstrate the solutions to both of these problems. In particular, we present a method to design masks with practical minimal feature sizes and show new manufactured masks with few defects. These masks were installed at HCIT and tested using more sophisticated wavefront control algorithms based on energy minimization of light in the dark zone. We present the results of these experiments, notably a record 2.4×10-9 contrast in 10% broadband light.
Direct imaging and characterization of exo-solar terrestrial planets require coronagraphic instruments capable
of suppressing star light to 10-10. Pupil shaping masks have been proposed and designed1 at Princeton
University to accomplish such a goal. Based on Princeton designs, free standing (without a substrate) silicon
masks have been fabricated with lithographic and deep etching techniques. In this paper, we discuss the
fabrication of such masks and present their physical and optical characteristics in relevance to their
performance over the visible to near IR bandwidth.
Spatial filtering is necessary to achieve deep nulls in optical interferometer and single mode infrared fibers can serve as
spatial filters. The filtering function is based on the ability of these devices to perform the mode-cleaning function: only
the component of the input field that is coupled to the single bound (fundamental) mode of the device propagates to the
output without substantial loss. In practical fiber devices, there are leakage channels that cause light not coupled into
the fundamental mode to propagate to the output. These include propagation through the fiber cladding and by means
of a leaky mode. We propose a technique for measuring the magnitude of this leakage and apply it to infrared fibers
made at the Naval Research Laboratory and at Tel Aviv University. All measurements are performed at 10.5 μm
The characteristics of Electro-actuated polymers (EAP) are typically considered inadequate for applications in robotics. But in recent years, there has been both dramatic increases in EAP technological capbilities and reductions in power requirements for actuating bio-inspired robotics. As the two trends continue to converge, one may anticipate that dramatic breakthroughs in biologically inspired robotic actuation will result due to the marraige of these technologies. This talk will provide a snapshot of how EAP actuator scientists and roboticists may work together on a common platform to accelerate the growth of both technologies. To demonstrate this concept of a platform to accelerate this convergence, the authors will discuss their work in the niche application of robotic facial expression. In particular, expressive robots appear to be within the range of EAP actuation, thanks to their low force requirements. Several robots will be shown that demonstrate realistic expressions with dramatically decreased force requirements. Also, detailed descriptions will be given of the engineering innovations that have enabled these robotics advancements-most notably, Structured-Porosity Elastomer Materials (SPEMs). SPEM manufacturing techniques create delicate cell-structures in a variety of elastomers that maintain the high elongation characteristics of the mother material, but because of the porisity, behave as sponge-materials, thus lower the force required to emulate facial expressions to levels output by several extant EAP actuators.
The development and fabrication of microfabricated propulsion components at the Jet Propulsion Laboratory is reviewed. These include a vaporizing liquid micro-thruster, which vaporizes propellant to produce thrust. Thrust performances of 32 (mu) N for an input power of 0.8 W were measured. Miniature solenoid and latch valves are being developed by Moog, Inc. in collaboration with JPL.
The MEMS Technology Group is part of the Microdevices Laboratory (MDL) at the Jet Propulsion Laboratory (JPL). The group pursues the development of a wide range of advanced MEMS technologies that are primarily applicable to NASA's robotic as well as manned exploration missions. Thus these technologies are ideally suited for the demanding requirements of space missions namely, low mass, low power consumption and high reliability, without significant loss of capability. End-to-end development of these technologies is conducted at the MDL, a 38,000 sq. ft. facility with approximately 5500 sq. ft. each of cleanroom (class 10 - 100,000) and characterization laboratory space. MDL facilities include computer design and simulation tools, optical and electron-beam lithography, thin film deposition equipment, dry and wet etching facilities including Deep Reactive Ion Etching, device assembly and testing facilities. Following the fabrication of the device prototypes, reliability testing of these devices is conducted at the state-of-the-art Failure Analysis Laboratory at JPL.