The Space Interferometry Mission (SIM) requires fringe measurements to the level of picometers in order to produce astrometric data at the micro-arc-second level. To be more specific, it is necessary to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer to a few hundreds of picometers. The internal path is measured with a small heterodyne metrology beam, whereas the starlight fringe position is estimated with a CCD sampling a large concentric annular beam. One major challenge for SIM is to align the metrology beam with the starlight beam to keep the consistency between these two sensors at the system level while articulating the instrument optics over the field of view. The Micro-Arcsecond Metrology testbed (MAM) developed at the Jet Propulsion Laboratory, California Institute of Technology, features an optical interferometer with a white light source, all major optical components of a stellar interferometer and heterodyne metrology sensors. The setup is installed inside a large vacuum chamber in order to mitigate the atmospheric and thermal disturbances. Wide angle astrometric observations are simulated by articulating the optics over the 15 degrees field of regard to generate multiple artificial stars. Recent data show agreement between the metrology and starlight paths to 350pm in the full wide angle field of view of SIM. This paper describes the MAM optical setup, the observation process, the current data and how the performance relates to SIM.
SIM-Lite missions will perform astrometry at microarcsecond accuracy using star light interferometry. For typical
baselines that are shorter than 10 meters, this requires to measure optical path difference (OPD) accurate to tens of
picometers calling for highly accurate calibration. A major challenge is to calibrate the star spectral dependency
in fringe measurements - the spectral calibration. Previously, we have developed a spectral calibration and
estimation scheme achieving picometer level accuracy. In this paper, we present the improvements regarding the
application of this scheme from sensitivity studies. Data from the SIM Spectral Calibration Development Unit
(SCDU) test facility shows that the fringe OPD is very sensitive to pointings of both beams from the two arms of
the interferometer. This sensitivity coupled with a systematic pointing error provides a mechanism to explain the
bias changes in 2007. Improving system alignment can effectively reduce this sensitivity and thus errors due to
pointing errors. Modeling this sensitivity can lead to further improvement in data processing. We then investigate
the sensitivity to a model parameter, the bandwidth used in the fringe model, which presents an interesting trade
between systematic and random errors. Finally we show the mitigation of calibration errors due to system drifts
by interpolating instrument calibrations. These improvements enable us to use SCDU data to demonstrate that SIM-Lite missions can meet the 1pm noise floor requirement for detecting earth-like exoplanets.
SIM Lite is a space-borne stellar interferometer capable of searching for Earth-size planets in the habitable zones of
nearby stars. This search will require measurement of astrometric angles with sub micro-arcsecond accuracy and optical
pathlength differences to 1 picometer by the end of the five-year mission. One of the most significant technical risks in
achieving this level of accuracy is from systematic errors that arise from spectral differences between candidate stars and
nearby reference stars. The Spectral Calibration Development Unit (SCDU), in operation since 2007, has been used to
explore this effect and demonstrate performance meeting SIM goals. In this paper we present the status of this testbed
and recent results.
KEYWORDS: MATLAB, Computing systems, Cameras, Data storage, Data processing, Data acquisition, Distributed computing, Human-machine interfaces, Control systems, Real-time computing
In the course of fulfilling its mandate, the Spectral Calibration Development Unit (SCDU) testbed for SIM-Lite produces
copious amounts of raw data. To effectively spend time attempting to understand the science driving the data, the team
devised computerized automations to limit the time spent bringing the testbed to a healthy state and commanding it,
and instead focus on analyzing the processed results. We developed a multi-layered scripting language that emphasized
the scientific experiments we conducted, which drastically shortened our experiment scripts, improved their readability,
and all-but-eliminated testbed operator errors. In addition to scientific experiment functions, we also developed a set of
automated alignments that bring the testbed up to a well-aligned state with little more than the push of a button. These
scripts were written in the scripting language, and in Matlab via an interface library, allowing all members of the team to
augment the existing scripting language with complex analysis scripts. To keep track of these results, we created an easilyparseable
state log in which we logged both the state of the testbed and relevant metadata. Finally, we designed a distributed
processing system that allowed us to farm lengthy analyses to a collection of client computers which reported their results
in a central log. Since these logs were parseable, we wrote query scripts that gave us an effortless way to compare results
collected under different conditions. This paper serves as a case-study, detailing the motivating requirements for the
decisions we made and explaining the implementation process.
The SIM-Lite astrometric interferometer will search for Earth-size planets in the habitable zones of nearby stars. In this
search the interferometer will monitor the astrometric position of candidate stars relative to nearby reference stars over
the course of a 5 year mission. The elemental measurement is the angle between a target star and a reference star. This is
a two-step process, in which the interferometer will each time need to use its controllable optics to align the starlight in
the two arms with each other and with the metrology beams. The sensor for this alignment is an angle tracking CCD
camera. Various constraints in the design of the camera subject it to systematic alignment errors when observing a star of
one spectrum compared with a start of a different spectrum. This effect is called a Color Dependent Centroid Shift
(CDCS) and has been studied extensively with SIM-Lite's SCDU testbed. Here we describe results from the simulation
and testing of this error in the SCDU testbed, as well as effective ways that it can be reduced to acceptable levels.
KEYWORDS: Calibration, Spectral calibration, Data modeling, Fourier transforms, Wavefronts, Charge-coupled devices, Optical filters, Monte Carlo methods, Modulation, Signal detection
The SIM PlanetQuest Mission will perform astrometry to one microarcsecond accuracy using optical interferometers
requiring optical path delay difference (OPD) measurements accurate to tens of picometers. Success
relies on very precise calibration. Spectral Calibration Development Unit (SCDU) has been built to demonstrate
the capability of calibrating spectral dependency of the white light fringe OPD to accuracy better than 20pm.
In this article, we present the spectral calibration modeling work for SCDU to achieve the SIM PlanetQuest
Engineering Milestone 4. SCDU data analysis shows that the wave front aberrations cause the instrument phase
dispersions to vary by tens of nanometers over the bandwidth of a CCD pixel making the previous model inadequate.
We include the effect of the wave front aberrations in the white light fringe model and develop a
procedure for calibrating the corresponding model parameters using long stroke fringe data based on Discrete
Fourier Transform. We make the calibration procedure flight traceable by dividing the whole calibration into the
instrument calibration and the source spectral calibration. End-to-end simulations are used to quantify both
the systematic and random errors in spectral calibration. The efficacy of the calibration scheme is demonstrated
using the SCDU experimental data.
SCDU (Spectral Calibration Development Unit) is a vacuum test bed that was built and operated for the SIM-Planetquest
Mission and has successfully demonstrated the calibration of spectral instrument error to an accuracy of
better than 20 picometers. This performance is consistent with the 1 micro-arc second goal of SIM. The calibration
procedure demonstrated in the test bed is traceable to the SIM flight instrument. This article is a review of all aspects of
the design and operation of the hardware as well as the methodology for spectral calibration. Spectral calibration to
better than 20 picometers and implications for flight are discussed.
This paper will present the analysis results taken from a well-designed interferometer SCDU. The
objective is to deliver picometer performance to meet the allocated astrometric error budget from SIM
PlanetQuest mission. It will describe the validation of optical designs and analysis procedures to achieve
high accuracy of the tip-tilt and shear alignments. Then it will enumerate environmental factors essential to
the SCDU performances. Finally it will report color-independent 3 picometer Narrow Angle (NA)
performance and all-in-one 17 picometer NA performance. The all-in-one pico-performance will require
spectral calibration modeling to remove delay differential induced by color.
The Space Interferometry Mission (SIM) requires fringe measurements to the level of picometers in order to produce astrometric data at the micro-arc-second level. To be more specific, it is necessary to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer to tens of picometers. The internal path is measured with a small heterodyne metrology beam, whereas the starlight fringe position is estimated with a CCD sampling a large concentric annular beam. One major challenge for SIM is to align the metrology beam with the starlight beam to keep the consistency between these two sensors at the system level while articulating the instrument optics over the field of regard.
The Micro-Arcsecond Metrology testbed (MAM), developed at the Jet Propulsion Laboratory, features an optical interferometer with a white light source, all major optical components of a stellar interferometer and heterodyne metrology sensors. The setup is installed inside a large vacuum chamber in order to mitigate the atmospheric and thermal disturbances. Astrometric observations are simulated by articulating the optics over the 15 degrees field of regard to generate multiple artificial stars. Recent data show agreement between the metrology and starlight paths to 20pm in the narrow angle field and to 350pm in the full wide angle field of regard of SIM. This paper describes the MAM optical setup, the observation process, the current data and how the performance relates to SIM.
The Space Interferometry Mission (SIM), scheduled for launch in early 2010, is an optical interferometer that will perform narrow angle and global wide angle astrometry with unprecedented accuracy, providing differential position accuracies of 1 uas, and 4 uas global accuracies in position, proper motion and parallax. SIM astrometric measurements are sythesized from pathlength delay measurements provided by three Michelson-type, white light interferometers. Two of the interferometers are used for making precise measurements of variations in the spacecraft attitude, while the third interferometer performs the science measurement. The ultimate performance of SIM relies on a combination of precise fringe measurements of the interfered starlight with picometer class relative distance measurements made between a set of fiducials that define the interferometer baseline vectors. The focus of the present paper is on the development and analysis of algorithms for accurate white light estimation, and on the preliminary validation of these aglorithms on the MicroArcsecond Testbed.
One of the most critical technology requirements for the Space Interferometry Mission is that the difference in pathlength traveled by the starlight through each arm of the instrument be known with picometers of precision. SIM accomplishes this by using an internal laser metrology system to measure the optical path traveled by the starlight. The SIM technology program has previously demonstrated laser gauges with measurement accuracy below 10 picometers. The next challenge is to integrate one of these gauges into a full interferometer system and demonstrate that the system still operates at the required level. For SIM, the ultimate requirement is that the internal metrology system be able to give an accurate measure of the starlight internal path difference to about 150 picometers over its narrow-angle field, with a goal of 50 picometer accuracy. This accuracy must be maintained even as SIM's various active systems articulate the SIM optics and vary the SIM internal pathlengths.
The Microarcsecond Metrology Testbed (MAM) is a full single-baseline interferometer coupled with a precision pseudostar, intended to demonstrate the level of agreement between starlight and metrology phase measurements needed to make microarcsecond-level measurements of stellar positions. MAM has been under development for several years and is now producing picometers-level consistency that translates into microarcseconds-level performance. This paper will present an overview of the MAM Testbed, together with recent results targeting the 150 picometer performance level required by SIM.
MAM is a dedicated systems-level testbed that combines the major SIM subsystems including laser metrogy, pointing, and pathlength control. The testbed is configured as a modified Michelson interferometer for the purpose of studying the white-light fringe measurement processes. This paper will compare the performance of various algorithms using the MAM data, and will aid in our recommendation of how the SIM flight system should process the science and guide interferometer data.
The Space Interferometry Mission (SIM) relies on interferometry and metrology capable of measuring the change in the optical path difference with picometer accuracy. For the last two years we designed and built the Micro-Arcsecond Metrology Testbed, the key technology demonstration for SIM. In a parallel effort the data analysis code was written. The interferometer was first used in a modified configuration; white light and light from a HeNe-laser was emerging from a fiber, collimated and split into the two arms with their respective delay lines. The recombined light was then dispersed onto the CCD camera. The tests done using this interferometer resulted in data on the effects that influence the accurate determination of the fringe phase delay: (1) alignment effects; (2) CCD camera parameters; (3) path length stability, and (4) analysis related inaccuracies. While offsetting the interferometer from equal arm length, the OPD was dithered using PZT-actuated mirrors. The white-light fringe was captured for each step. At the same time the (HeNe) laser light was monitored with two photo detectors--one serving as an intensity monitor, the second one monitoring the interfered laser light. This technique was used to accurately measure the path length changes by analyzing the linear parts of the HeNe sinusoidal interference signal normalized by the HeNe intensity signal. This simple metrology system is designed to determine the optical path length changes to about 100 pm.
We derive a visual image quality metric from a model of human visual processing that takes as its input an original image and a compressed or otherwise altered version of that image. The model has multiple channels tuned to spatial frequency, orientation and color. Channel sensitivities are scaled to match a bandpass achromatic spatial frequency contrast sensitivity function (CSF) and lowpass chromatic CSFs. The model has a constant gain control with parameters based on the results of human psychophysical experiments on pattern masking and contrast induction. These experiments have shown that contrast gain control within the visual system is selective for spatial frequency, orientation and color. The model accommodates this result by placing a contrast gain control within each channel and by letting each channel's gain control be influenced selectively by contrasts within all channels. A simple extension to this model provides predictions of color image quality.
We present results of a scheme to encode video sequences of digital image data based on a quadtree still-image fractal method. The scheme encodes each frame using image pieces, or vectors, from its predecessor; hence it can be thought of as a VQ scheme in which the code book is derived from the previous image. We present results showing: near real-time (5 - 12 frames/sec) software-only decoding; resolution independence; high compression ratios (25 - 244:1); and low compression times (2.4 - 66 sec/frame) as compared with standard fixed image fractal schemes.
The paper contains a brief description of fractal image compression methods with sample compression results. We also present comparative results between two fractal schemes, discrete cosine transform and a wavelet method. We show that, with the PSNR as a measure of image quality, some fractal schemes perform best over the range of compressions of most interest.
Polyacetylene is one of the most studied nonlinear organic materials. Its nearly one- dimensional nature and the conjugate electrons along the carbon-backbone are responsible for its unusual physical, chemical, and optical properties. Polyacetylene has attracted the attention of physicists, chemists, and optical engineers. In particular, the highly nonlinear optical properties of polyacetylene can imply efficient optoelectronic applications.
It is now well known that a novel class of solid-state integrated devices in radar, electronic warfare, and communication systems can be constructed using linear or nonlinear magnetostatic guided waves or surface waves as their basis. Such waves can propagate in magnetic thin films in the microwave bands. The liquid phase epitaxy (LPE) technology now exists for the preparation of high quality thin films in the microwave bands as well as high quality thin films of yttrium-iron-garnet (YIG). This fact permits the construction of devices in integrable compact form with very low loss. In this review, important theoretical foundations based on the perturbative wave-mixing method for nonlinear magnetic interactions are laid. The second-order magnetic effects may result in the resonant forced second-order nonlinearities. The third-order self-action effects may lead to longitudinal modulation instability and possible soliton formation. The third-order wave-mixing effects can be used to generate phase conjugated wave for signal processing and communication applications. The potential of these nonlinear magnetic effects for new nonlinear microwave devices is very briefly discussed.
The wave equation of nonlinear magnetostatic surface waves (MSSW) on ferromagnetic films is derived for the first time and its solution is found. The nonlinear dispersion relation of MSSW is discussed.
Recently, energy transfer has been observed between two pulsed, degenerate laser beams
copropagating almost collinearly into isotropic Kerr media with temporal relaxation.
Theoretical calculations have been made which agree with the experimental data. This paper
will briefly describe the experiment, and develop the theory which simulates the lab situation.
The physical mechanism regulating this beam combination will also be discussed. Comparisons
between the numerical simulations and the experimental data will also be presented.
Optical phase conjugation at microwave and millimeter wavelengths offers numerous
applications for communications, radar and navigation. Recently, we have examined the
feasability of achieving phase conjugation at typical radar wavelengths ulitizing magnetic thin
films as the active medium. Our calculations indicate that magnetic materials are unusally
promising for generating phase conjugate radiation at microwave frequencies.
A general theory for coherent coupling between two co-propagating or counterpropagating
guided waves is formulated within the slowly varying envelope approximation. A pair of coupled
nonlinear equations is obtained for the evolution of envelope functions. A numerical result is
given for coherent coupling of two co-propagating pulses in a single mode fiber.
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