The design of precision optical gauges for metrology is facilitated by predictions of performance by means of computer simulation. For example, consequences of design parameter variations can be investigated before committing to the time and expense of hardware fabrication or procurement. Once the components are assembled, puzzling test results may be understood by simulating various misalignments. Classical geometric optical ray trace analysis of these systems is not capable of predicting diffraction effects which are important in determining the ultimate achievable metrology precision. We present details of a simulation approach which we have developed for the diffraction analysis of such systems. Optical signals are represented as two-dimensional scalar fields, and paraxial scalar diffraction theory is used to calculate the propagation of signals -- through various optical elements, such as apertures, lenses and corner cubes - to detector focal planes. The simulation includes coherent combination of signal and local reference wavefronts at the focal plane, and modeling the measurement of optical phase by heterodyne detection - a capability critical to optical metrology. We discuss the capabilities, limitations and sources of error inherent in our approach; present the results of modeling one or more metrology systems which are currently under laboratory development; indicate how simulation can identify sources and magnitudes of measurement error; and show correspondence of simulations with laboratory measurement.
Visible interferometry at µarc-second accuracy requires measurement of the interferometric baseline length and orientation at picometer accuracy. The optical metrology instruments required for these interferometers must achieve accuracy on order of 1 to 10 picometers. This paper discusses the progress in the development of optical interferometers for use in distance measurement gauges with systematic errors below 100 picometers. The design is discussed as well as test methods and test results.
To accomplish micro-arcsecond astrometric measurement, stellar interferometers such as SIM require the measurement of internal optical path length delay with an accuracy of ~10 picometers level. A novel common-path laser heterodyne interferometer suitable for this application was proposed and demonstrated at JPL. In this paper, we present some of the experimental results from a laboratory demonstration unit and design considerations for SIM's internal metrology beam launcher.
The ABL Lockheed Martin has prepared and validated a highly versatile adaptive optics testbed to simulate in an accurately scaled fashion all aspects of ABL laser beam propagation, including atmospheric compensation and pointing and tracking in selected atmospheres. This system allows repetitive, highly controlled, and well diagnosed experiments to be carried out that are generally impossible to do in field test where the user has little control over atmospheric and other test conditions. Testing of beam control hardware including components, assemblies, control loops and software, as well as development of methodology such as alignment and sensor techniques, determinations of system operational robustness, and finally, measurement of overall system performance under various atmospheric or other propagation and seeing conditions are routinely done. This presentation will discuss 1) the system scaling chosen to preserve diffraction, turbulence and temporal fidelity to ABL, 2) agreement of experiment results to those of other laser propagation experiments and wave optic code simulations, and 3) experiments that have demonstrated ABL beam control system robustness, compensation for jitter and turbulence, and overall performance when operating in atmospheric turbulence that emulates that measured in the real-world theater.
A common method for storing knowledge in databases is in the form of attribute values. For databases with spatial and temporal knowledge however, it is not feasible to store all of the attribute values that one might be interested in. For example, in the spatial domain for a geographic database it is impossible to anticipate the very large number of queries regarding nearness, spatial adjacency, or the possibility of finding feasible paths between arbitrary locations. Similarly in the temporal domain it is impossible to anticipate all queries regarding the temporal duration, range, and overlap of complex temporal events. We have developed both spatial and temporal representations for databases to handle the inferring of attribute values as a result of possible queries. The temporal representation involves the creation of time tags for attribute values and information regarding the persistence of those values. The spatial representation consists of a labeled array in which each label corresponds to to a unique object (or class of objects) in the database. Preprocessing of spatial “scenes” allows the system to rapidly obtain paths, determine objects in a given region of interest, etc. These representations, and their application to typical geographic/temporal databases are described in the paper. A natural language interface, developed earlier, was extended to work with these spatial and temporal representations.