Conducting high resolution field microscopy with coupled laser spectroscopy that can be used to selectively analyze the
surface chemistry of individual pixels in a scene is an enabling capability for next generation robotic and manned
spaceflight missions, civil, and military applications. In the laboratory, we use a range of imaging and surface
preparation tools that provide us with in-focus images, context imaging for identifying features that we want to
investigate at high magnification, and surface-optical coupling that allows us to apply optical spectroscopic analysis
techniques for analyzing surface chemistry particularly at high magnifications. The camera, handlens, and microscope
probe with scannable laser spectroscopy (CHAMP-SLS) is an imaging/spectroscopy instrument capable of imaging
continuously from infinity down to high resolution microscopy (resolution of ~1 micron/pixel in a final camera format),
the closer CHAMP-SLS is placed to a feature, the higher the resultant magnification. At hand lens to microscopic
magnifications, the imaged scene can be selectively interrogated with point spectroscopic techniques such as Raman
spectroscopy, microscopic Laser Induced Breakdown Spectroscopy
(micro-LIBS), laser ablation mass-spectrometry,
Fluorescence spectroscopy, and/or Reflectance spectroscopy. This paper summarizes the optical design, development,
and testing of the CHAMP-SLS optics.
The Space Interferometry mission's nano-meter class System Testbed has implemented an external metrology system to monitor changes in the length & orientation of the science interferometer baseline vector, which cannot be monitored directly. The output of the system is used in real time fringe tracking of dim stars. This paper describes the external metrology system, its mathematical representation, limitations, and method for estimating the length & orientation of the science baseline vector. Simulations and current system performance are presented and discussed.
Future space-based optical instruments such as the Space Interferometer Mission have vibration-induced error allocations at the levels of a few nano-meters and milli-arc-seconds. A dual stage passive isolation approach has been proposed using isolation first at the vibration-inducing reaction wheels, and a second isolation layer between the bus portion of the space vehicle (the backpack) and the optical payload. The development of the backpack isolator is described, with unit transmissibility results for individual isolator struts. The dual stage isolation approach is demonstrated on a dynamically feature-rich, 7-meter structural testbed (STB3). A new passive suspension that mitigates ground vibrations above 0.4 Hz has been integrated into the testbed. A series of OPD performance predictions have been made using measured transfer functions. These indicate that the 5-nm dynamic OPD allocation is within reach using the dual isolator approach. Demonstrating these low response levels in a noisy air environment has proven to be difficult. We are sequentially executing a plan to mitigate acoustic transmission between backpack and flight structure, as well as developing techniques to mitigate effects of background acoustic noise.
TThe SIM Interferometry Test Bed 3 (STB3) is the spaceborne-stellar-interferometer simulator for SIM, built and operating at JPL. Its construction details and performance are described elsewhere in this conference. The test bed consists of an interferometer system built on a large optical table, and a star simulator built on another large optical table placed directly across it. The optical tables float on
independent, air-filled suspension legs simulating the SIM spacecraft and the distant stars it is to observe. In order to demonstrate the performance requirements, a novel attitude control system (ACS) has been built and installed on the STB3. In this paper, the details of the design, construction and performance of the attitude control system are presented. The attitude control system has been used to meet certain SIM requirements. An example of this performance test is also included.
The Stellar Interferometry Mission (SIM) and particularly one of its testbeds require compound optical pieces the construction and qualification of which, in turn, require very high-precision absolute surface metrology gauges. In this paper, the details of the design, construction and performance of a triplet of interferometers capable of performing the required measurements are presented.
Active wavefront correction of a space telescope provides a technology path for extremely high contrast imaging astronomy at levels well beyond the capabilities of current telescope systems. A precision deformable mirror technology intended specifically for wavefront correction in a visible/near-infrared space telescope
has been developed at Xinetics and extensively tested at JPL over the past several years. Active wavefront phase correction has been demonstrated to 1 Angstrom rms over the spatial frequency range accessible to a mirror with an array of actuators on a 1 mm pitch. It is based on a modular electroceramic design that is scalable to
1000s of actuator elements coupled to the surface of a thin mirror facesheet. It is controlled by a low-power multiplexed driver system. Demonstrated surface figure control, high actuator density, and low power dissipation are described. Performance specifications are discussed in the context of the Eclipse point design for a coronagraphic space telescope.
Keck Interferometer differential-phase planet-detection system requires a picometer accuracy, large (2 μm to 4 μm) amplitude optical path-length modulator that can operate at fairly high frequencies (250 Hz, 750 Hz, and 1250 Hz, a partial, triangular wave motion).
We have developed a gauge which monitors the amplitude of the motion of the path-length modulator and which is capable of reaching a sensitivity of at least 3 pm per sqrt(Hz) within a band width of 1 Hz at 250 Hz, 750 Hz, and 1250 Hz. Two of these gauges are built. The gauges are compared to each other while monitoring a common optical path-length modulator to determine their accuracy.
In this paper, the gauge construction details, the results of the gauge accuracy tests as well as the final path-length modulator performance details are presented.
The proposed Space Interferometry Mission (SIM) spacecraft designs include high resolution stellar interferometers for micro-arc-second accuracy astrometric measurements. The stellar interferometers require picometer accuracy 1D metrology gauges, surface metrology gauges and 3D metrology gauges to measure the required distances or to calibrate the fiducials that define the end points of the interferometric paths. The absolute metrology gauges required by these interferometers can be considerably less accurate due to the careful design of the astrometric interferometers and the fiducials on the spacecraft. An auto-aligning, 3D metrology gauge constructed using the sub-picosecond linear metrology gauges was described in earlier papers. The sub-nanometer, in-vacuum tracking result from this 3D metrology gauge are presented. The resulting jitter is analyzed and is shown to be caused by thermal drift in the alignment of the gauge heads, warpage of the base table and the time-dependent tilt of the experiment as a whole. The aberrations in the light beams of the laser distance gauges can result in errors in the distance measurements performed using these gauges. Simulations using spot shapes and aberrations present in a realistic measurement system used in a stellar interferometer is space are performed to quantify the amount of expected errors. The results of these simulations are presented.
The Palomar Testbed Interferometer (PTI) is an infrared, phase-tracking interferometer in operation at Palomar Mountain since July 1995. It was funded by NASA for the purpose of developing techniques and methodologies for doing narrowangle astrometry for the purpose of detecting extrasolar planets. The instrument employs active fringe trackingin the infrared (2.0-2.4 μm) to monitor fringe phase. It is a dual-star interferometer; it is able to measure fringes on two separate stars simultaneously. An end-to-end heterodyne laser metrology system is used to monitor the optical path length of the starlight. Recently completed engineering upgrades have improved the initial instrument performance. These upgrades are:extended wavelength coverage, a single mode fiber for spatial filtering, vacuum pipes to relay the beams, accelerometers on the siderostat mirrors and a new baseline. Results of recent astrometry data indicate the instrument is approaching the astrometric limit as set by the atmosphere.
The Space Interferometry Mission (SIM) relies on the combination of interferometry with a metrology system capable of measuring picometer relative length changes and micrometer absolute lengths. We are designing the Micro-Arcsec Metrology Test-Bed (MAM) to put these two systems together in a large vacuum tank (12m long, 2.4m in diameter). The interferometer has a 1.8 m baseline and is looking at an artificial star 10 m away. The metrology system is measuring the distances between the interferometer mirrors, the interferometer mirrors and the 'star' (external metrology), and the interferometer arm lengths(internal metrology). We are using two common path laser heterodyne interferometers to monitor each of these distances. The light sources used are two Nd:YAG lasers with different frequencies, f0 and F0 + 30 GHz. This allows measurement of relative lengths changes as well as absolute lengths. The design for the heterodyne interferometers is in progress using our experience from 1-D and 3-D metrology experiments performed in the past. Modifications include reducing the cross-talk in the internal metrology and adding a polarizing beamsplitter to the laser light path to compensate for path lengths changes caused by temperature changes.
The micro-arcsecond metrology testbed (MAM) is a high- precision long baseline interferometer inside a vibration- isolated vacuum tank. The instrument consists of an artificial star, a laser metrology system, and a single- baseline interferometer with a 1.8m baseline and a 5cm clear aperture. MAM's purpose is to demonstrate that the astrometric error budget specified for the Space Interferometry Mission can be met.
The proposed Space Interferometry Mission (SIM) spacecraft carries high resolution stellar interferometers for micro-arc- second accuracy astrometric measurements. These stellar interferometers require picometer accuracy one dimensional metrology gauges, surface metrology gauges and 3-dimensional metrology gauges. The absolute metrology gauges required by these interferometers can be considerably less accurate due to the careful design of the astrometric interferometers on the spacecraft. Open-faced, hollow corner cube retro-reflectors are used as fiducials in the one-dimensional relative and absolute metrology gauges and the 3-dimensional metrology gauge. The diffraction caused by the assembly and the component defects of these hollow retro-reflectors affects the accuracy of these metrology gauges. A simulation quantifying some of the effects of the component and assembly defects of hollow retro-reflectors on the accuracy of a picometer linear metrology gauge is presented. An auto-aligning, 3-dimensional metrology gauge constructed using the sub-picometer linear metrology gauges was described in earlier papers. The functioning automatic alignment and the sub-nanometer, in-air tracking results from this 3-dimensional metrology gauge are presented.
Very high resolution spatial interferometry requires picometer level 1D metrology, surface metrology and 3D metrology. The absolute distance measurements with accuracies of only 1 part in a million are required due to the careful design of spacecraft like the proposed Stellar Interferometry Mission, carrying high resolution stellar interferometers. An absolute calibration system for the surface gauge described in a previous paper is demonstrated. A self-calibrating absolute metrology system with a repeatability of 2 microns rms over a one-way distance of a meter is demonstrated. The accuracy calibration of this gauge is in progress. An auto-aligning, 3D metrology gauge is constructed using the sub-picometer linear metrology gauge described in earlier papers. Initial test results from this demonstration are presented.
Very high resolution spatial interferometry requires picometer level 1D metrology, surface metrology and 3D metrology. Micron level accuracy is required for absolute metrology systems for spacecraft like the proposed Orbiting Stellar Interferometer carrying high resolution spatial interferometers. A surface metrology system with a repeatability of less than 0.1 nm over an aperture of several inches in vacuum has been demonstrated. An absolute calibration system for this gauge is in development. An absolute metrology system with an accuracy of 10 microns over a distance of 10 meters is also under construction. This system uses a 1319 nm, solid-state, infrared laser locked to an Ultra-Low-Expansion glass cavity to an accuracy exceeding 1 part in 1010. The length of the cavity is controlled by a thermal vacuum oven. 1 millidegree Centigrade root-mean-squared (rms) cavity temperature stability with the oven in vacuum has been achieved for time scales of days. The digital laser servo is capable of following the length of the cavity with an Allen deviation of few hundred Hertz for time scales of a day. Two lasers locked to the same cavity are used to supply a simultaneous cavity length measurement as well as the absolute distance measurement. The absolute distance measuring part of the gauge is under construction. An auto alignment system is being developed for our linear relative metrology gauge which had achieved an accuracy of 0.1 picometers. This gauge will be used to construct a 3D metrology gauge with an accuracy of less than 10 pm rms for time scales of minutes initially.
LATOR is a space-based experiment to accurately measure the gravitational deflectional deflection of light. The experiment uses two laser bearing spacecraft at the opposite side of the Sun and a very long baseline heterodyne interferometer to measure the angle at an accuracy of 0.2 uas. Combining this measurement with laser ranging from Earth to both spacecraft, gravitational deflection can be made with an accuracy 5000 times better than previously done and will allow measurements of the second order and frame dragging effects.
The ASEPS-O Testbed Interferometer is a long-baseline infrared interferometer optimized for high-accuracy narrow-angle astrometry. It is being constructed by JPL for NASA as a testbed for the future Keck Interferometer to demonstrate the technology for the astrometric detection of exoplanets from the ground. Recent theoretical and experimental work has shown that extremely high accuracy narrow-angle astrometry, at the level of tens of microarcseconds in an hour of integration time, can be achieved with a long-baseline interferometer measuring closely-spaced pairs of stars. A system with performance close to these limits could conduct a comprehensive search for Jupiter- and Saturn-mass planets around stars of all spectral types, and for short-period Uranus-mass planets around nearby M and K stars. The key features of an instrument which can achieve this accuracy are long baselines to minimize atmospheric and photon-noise errors, a dual-star feed to route the light from two separate stars to two beam combiners, cophased operation using an infrared fringe detector to increase sensitivity in order to locate reference stars near a bright target, and laser metrology to monitor systematic errors. The ASEPS-O Testbed Interferometer will incorporate these features, with a nominal baseline of 100 m, 50- cm siderostats, and 40-cm telescopes at the input to the dual- star feeds. The fringe detectors will operate at 2.2 micrometers , using NICMOS-III arrays in a fast-readout mode controlling high-speed laser-monitored delay lines. Development of the interferometer is in progress, with installation at Palomar Mountain planned to begin in 1994.
The accuracy of the relative metrology gauge developed for the proposed OSI and SONATA missions is improved to subpicometer level. An accuracy of 0.15 picometers is obtained in vacuum at time scales of a few minutes. A surface metrology gauge with an initial accuracy of (lambda) /1000 is under construction. Photometry accurate to better than 1 part in 103 for the surface metrology gauge is demonstrated using a commercial grade, 8-bit, uncooled CCD camera and a commercial grade frame grabber at time scales of 10 seconds with a resolution of 320 by 240 pixels.
Heterodyne interferometers have been commercially available for many years. In addition, many versions have been built at JPL for various projects. This activity is aimed at improving the accuracy of such interferometers from the 1 - 30 nanometer level to the picometer level for use in the proposed OSI and SONATA missions as metrology gauges. In the null-gauge configuration, we obtained a precision of 0.6 picometers at time scales of 2,500 seconds. In the relative-gauge configuration, we obtained an accuracy of 3.5 picometers rms in vacuum at time scales of few minutes. As absolute gauge with an accuracy of 10 microns over a distance of 10 meters in under construction.
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