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Laser-cooled atoms are used as freefall test masses. The gravitational acceleration on atoms is measured by atom-wave interferometry. The fundamental concept behind atom interferometry is the quantum mechanical particle-wave duality. One can exploit the wave-like nature of atoms to construct an atom interferometer based on matter waves analogous to laser interferometers.
A second-harmonic generator (SHG) serves as the source of the visible laser beam in an onboard calibration scheme for NASA's planned Space Interferometry Mission (SIM), which requires an infrared laser beam and a visible laser beam coherent with the infrared laser beam. The SHG includes quasi-phase-matched waveguides made of MgO-doped, periodically poled lithium niobate, pigtailed with polarization- maintaining optical fibers. Frequency doubling by use of such waveguides affords the required combination of coherence and sufficient conversion efficiency for the intended application. The spatial period of the poling is designed to obtain quasi-phase- matching at a nominal middle excitation wavelength of 1,319.28 nm. The SHG is designed to operate at a warm bias (ambient temperature between 20 and 25 C) that would be maintained in its cooler environment by use of electric heaters; the heater power would be adjusted to regulate the temperature precisely and thereby maintain the required precision of the spatial period. At the state of development at the time of this reporting, the SHG had been packaged and subjected to most of its planned space-qualification tests.
Fringe visibility dependence on path length difference in laser illuminated two-beam interferometer
The Laser Interferometer Space Antenna (LISA) is a proposed detector of gravitational waves in the 0.1 mHz - 0.1 Hz band. LISA will measure gravitational wave strain at the 10(exp -21) level by monitoring the distance between freely-falling test masses s(exp -11) m. These distance measurements will be made using heterodyne interferometry with multiple light sources on moving platforms with changing baselines, all of which cause frequency noise to couple into the displacement measurement. I will describe how LISA interferometry mitigates the effects of laser frequency noise through active suppression and common mode rejection. Recent laboratory developments will also be discussed.
Planetary and lunar ephemerides are no longer used for the determination of inertial space. Instead, the new fundamental reference frame, the International Celestial Reference Frame (ICRF), is inherently less susceptible to extraneous, non-inertial rotations than a dynamical reference frame determined by the ephemerides would be. Consequently, the ephemerides are now adjusted onto the ICRF, and they are fit to two modern, accurate observational data types: ranging (radar, lunar laser, spacecraft) and Very Long Baseline Interferometry (VLBI) (of spacecraft near planets). The uncertainties remaining in the inner planet ephemerides are on the order of 1 kilometer, both in relative positions between the bodies and in the orientation of the inner system as a whole. The predictive capabilities of the inner planet ephemerides are limited by the uncertainties in the masses of many asteroids. For this reason, future improvements to the ephemerides must await determinations of many asteroid masses. Until then, it will be necessary to constantly update the ephemerides with a continuous supply of observational data.
As part of the Crustal Dynamics Project, an experiment was performed to verify the ability of Satellite Laser Ranging (SLR), Very Long Baseline interferometry (VLBI) and Doppler Satellite Positioning System (Doppler) techniques to estimate the baseline distances between several locations. The Goddard Space Flight Center (GSFC) lasers were in operation at all five sites available to them. The ten baselines involved were analyzed using monthly orbits and various methods of selecting data. The standard deviation of the monthly SLR baseline lengths was at the 7 cm level. The GSFC VLBI (Mark III) data was obtained during three separate experiments. November 1979 at Haystack and Owens Valley, and April and July 1980 at Haystack, Owens Valley, and Fort Davis. Repeatability of the VLBI in determining baseline lengths was calculated to be at the 2 cm level. Jet Propulsion Laboratory (JPL) VLBI (Mark II) data was acquired on the Owens Valley to Goldstone baseline on ten occasions between August 1979 and November 1980. The repeatability of these baseline length determinations was calculated to be at the 5 cm level. National Geodetic Survey (NGS) Doppler data was acquired at all five sites in January 1980. Repeatability of the Doppler determined baseline lengths results were calculated at approximately 30 cm. An intercomparison between baseline distances and associated parameters was made utilizing SLR, VLBI, and Doppler results on all available baselines. The VLBI and SLR length determinations were compared on four baselines with a resultant mean difference of -1 cm and a maximum difference of 12 cm. The SLR and Doppler length determinations were compared on ten baselines with a resultant mean difference of about 30 cm and a maximum difference of about 60 cm. The VLBI and Doppler lengths from seven baselines showed a resultant mean difference of about 30 cm and maximum difference of about 1 meter. The intercomparison of baseline orientation parameters were consistent with past analysis.
The proposed New Millenium Interferometry consists of three spacecraft separated by up to several kilometers. A heterodyne laser metrology system is proposed to measure the relative distances between the spacecraft.
The Terrestrial Planet Finder (TPF) employs an aggressive coronagraph designed to obtain better than 1e-10 contrast inside the third Airy ring. Minute changes in low-order aberration content scatter significant light at this position. One implication is the requirement to control low-order aberrations induced by motion of the secondary mirror relative to the primary mirror; sub-nanometer relative positional stability is required. We propose a 6-beam laser truss to monitor the relative positions of the two mirrors. The truss is based on laser metrology developed for the Space Interferometry Mission.
Beam splitter employing birefringent optics provides either widely different or precisely equal beam ratios, it can be used with laser light source systems for interferometry of lossy media, holography, scattering measurements, and precise beam ratio applications.
Holographic interferometry, improved coherence of ruby lasers, and instrumentation techniques
Work performed and data obtained in geodynamic research is reported. The purpose was to obtain utilization of: (1) laser and very long baseline interferometry (VLBI); (2) range difference observation in geodynamics; (3) development of models for ice sheet and crustal deformations. The effects of adopting new precession, nutation and equinox corrections on the terrestrial reference frame are investigated.
An analysis is given of how satellite, lunar laser, and very long base interferometry stations available during the MERIT Campaign in 1983/84 can contribute to the detection of short periodic variations in the rotational parameters of the earth, as well as the determination of the differences between the various Conventional Terrestrial and Inertial Reference Frames inherent in the above systems. Specific observational requirements are given both by objective and by country.
The current technical objectives for the geodynamics program consist of (1) optimal utilization of laser and Very Long Baseline Interferometry (VLBI) observations for reference frames for geodynamics; (2) utilization of range difference observations in geodynamics; and (3) estimation techniques in crustal deformation analysis.
The Crustal Dynamics Project has been developing, deploying, and operating very-long-baseline interferometry (VLBI) systems and satellite laser ranging (SLR) systems for highly accurate geodetic measurements of global plate motion, plate stability, regional crustal deformation, and earth rotation/polar motion. Over the past 10 years, the measurement accuracies of these systems have been improved by a factor of 10 to the cm level. Plans are to continue these developments to reach mm level accuracies. The present deployment of the VLBI systems is primarily in the Northern Hemisphere. This network has produced measurements of the relative plate motion between the North American, Eurasian, and Pacific plates; the stability of the same plates; and the regional deformation at the North American/Pacific plate boundary in California and Alaska.
Structural components in flight vehicles is often inherited flaws, such as microcracks, voids, holes, and delamination. These defects will degrade structures the same as that due to damages in service, such as impact, corrosion, and erosion. It is very important to know how a structural component can be useful and survive after these flaws and damages. To understand the behavior and limitation of these structural components researchers usually do experimental tests or theoretical analyses on structures with simulated flaws. However, neither approach has been completely successful. As Durelli states that 'Seldom does one method give a complete solution, with the most efficiency'. Examples of this principle is seen in photomechanics which additional strain-gage testing can only average stresses at locations of high concentration. On the other hand, theoretical analyses including numerical analyses are implemented with simplified assumptions which may not reflect actual boundary conditions. Hybrid-Numerical methods which combine photomechanics and numerical analysis have been used to correct this inefficiency since 1950's. But its application is limited until 1970's when modern computer codes became available. In recent years, researchers have enhanced the data obtained from photoelasticity, laser speckle, holography and moire' interferometry for input of finite element analysis on metals. Nevertheless, there is only few of literature being done on composite laminates. Therefore, this research is dedicated to this highly anisotropic material.
A Kalman filter has been used to combine independent measurements of the Earth's orientation taken by the space-geodetic observing techniques of lunar laser ranging, satellite laser ranging, very long baseline interferometry, and the Global Positioning System. Prior to their combination, the data series were adjusted to have the same bias and rate, the stated uncertainties of the measurements were adjusted, and data points considered to be outliers were deleted. The resulting combination, SPACE94, consists of smoothed, interpolated polar motion and UT1-UTC values spanning October 6, 1976, to January 27, 1995, at 1-day intervals. The Kalman filter was then used to combine the space-geodetic series comprising SPACE94 with two different, independent series of Earth orientation measurements taken by the technique of optical astrometry. Prior to their combination with SPACE94, the bias, rate and annual term of the optical astrometric series were corrected, the stated uncertainties of the measurements were adjusted, and data points considered to be outliers were deleted. The adjusted optical astrometric series were then combined with SPACE94 in two steps: (1) the Bureau International de l'Heure (BIH) optical astrometric series was combined with SPACE94 to form COMB94, a combined series of smoothed, interpolated polar motion and UT1-UTC values spanning January 20, 1962, to January 27, 1995, at 5-day intervals, and (2) the International Latitude Service (ILS) optical astrometric series was combined with COMB94 to form POLE94, a combined series of smoothed, interpolated polar motion values spanning January 20, 1900, to January 21, 1995, at 30.4375-day intervals.
Independent Earth-orientation measurements taken by the space-geodetic techniques of lunar and satellite laser ranging, very long baseline interferometry, and the global positioning system have been combined using a Kalman filter. The resulting combined Earth-orientation series, SPACE2001, consists of values and uncertainties for Universal Time, polar motion, and their rates that span from September 28.0, 1976 to January 19.0, 2002 at daily intervals. The space-geodetic measurements used to generate SPACE2001 have been combined with optical astrometric measurements to form two additional combined Earth-orientation series: (1) COMB2001, consisting of values and uncertainties for Universal Time, polar motion, and their rates that span from January 20.0, 1962 to January 15.0, 2002 at five-day intervals, and (2) POLE2001, consisting of values and uncertainties for polar motion and its rates that span from January 20, 1900 to December 21, 2001 at 30.4375-day intervals.
Independent Earth orientation measurements taken by the space-geodetic techniques of lunar and satellite laser ranging, very long baseline interferometry, and the global positioning system have been combined using a Kalman filter. The resulting combined Earth orientation series, SPACE2003, consists of values and uncertainties for Universal Time, polar motion, and their rates that span from September 28.0, 1976 to January 31.0, 2004 at daily intervals and is available in versions whose epochs are given at either midnight or noon. The space-geodetic measurements used to generate SPACE2003 have then been combined with optical astrometric measurements to form two additional combined Earth orientation series: (1) COMB2003, consisting of values and uncertainties for Universal Time, polar motion, and their rates that span from January 20.0, 1962 to January 31.0, 2004 at daily intervals and which is also available in versions whose epochs are given at either midnight or noon, and (2) POLE2003, consisting of values and uncertainties for polar motion and its rate that span from January 20, 1900 to January 21,2004 at 30.4375-day intervals.