Abstract:
An optical system includes a photolithography system, a low coherence interferometer, and a detector. The photolithography system is configured to illuminate a portion of an object with a light pattern and has a reference surface. The low coherence interferometer has a reference optical path and a measurement optical path. Light that passes along the reference optical path reflects at least once from the reference surface and light that passes along the measurement optical path reflects at least once from the object. The detector is configured to detect a low coherence interference signal including light that has passed along the reference optical path and light that has passed along the measurement optical path. The low coherence interference signal is indicative of a spatial relationship between the reference surface and the object.
Abstract:
For generating several interferograms which differ from each other in the relative phase position between the interfering partial beams, a light source is utilized having a coherence length less than the optical path difference between the two component beams in the measuring path of the interferometer. Furthermore, at least one optical delay device is provided which splits the beam into two component beams and which generates an optical path difference between these component beams which is approximately the same as the optical path difference of the partial beams in the measuring path of the interferometer. Thereafter, the delay device again unites the component beams congruently.
Abstract:
Interferometric apparatus and methodology for precisely measuring the shape of rotationally and non-rotationally symmetric optical surfaces comprising an illumination source with two wavelengths, a transmission flat with a reference surface, a basic optical system for producing a wavefront of predetermined shape, a compensation component having an aspheric wavefront shaping surface and an aspheric reference surface. The aspheric shaping surface modifies the predetermined wavefront so that it impinges on the aspheric reference surface with a shape substantially that same as that of aspheric reference surface. For a given aspheric reference surface, the radius or curvature and spacing of the aspheric shaping surface are optimized so that its aspheric departure is no larger than that of the aspheric reference surface. Precise alignment in six degrees of freedom is provided via feedback control.
Abstract:
Two bar patterns are projected sequentially on the object (O) to be measured, e.g., by time-division multiplexing, at angles which are inclined toward each other. The bar patterns are produced by projectors having respective rectangular gratings. The periods of the gratings are the same, and the phase relationship of the gratings is fixed relative to each other. Each reflected bar pattern, as distorted by the surface of the object, is individually and sequentially recorded by a camera (K); and the bar phases (.psi..sub.1, .psi..sub.2) of each sequentially reflected bar pattern are calculated for each image point by a computer connected with the camera. The computer also computes the differences (.DELTA..psi.) between the bar phases of the two projections for each image point. These phase differences remain stationary even when the bar patterns are moved relative to the camera. A plurality of phase differences for each image point is stored, averaged, and then used to calculate the height measurement (z) for each image point for display on a television monitor (42).
Abstract:
The invention relates to an evaluation method for interferograms and an interferometer corresponding thereto with which tile influence of coherent noise is reduced with simultaneously high interference contrast. Several phase maps are computed from interferograms which are recorded with coherent light. The interferogram components of the test object and the interferogram components of the coherent noise are displaced relative to each other in the camera plane between recording the interferograms. The influence of the coherent noise is suppressed by subsequently averaging the phase maps.
Abstract:
The present invention relates to a method for evaluating fringe images, in particular, for topographic measurements. During a first step, several phase-displaced patterns are recorded sequentially in time, and the respective phase relations of these patterns are determined by evaluation in the spatial domain (14a, 14b, 15). During a second step, after the phase shifts have been determined accurately in this manner based on the video images themselves, a pixel-by-pixel evaluation of the phase-displaced pattern is performed in the time domain. The invention also includes computer hardware for performing the evaluation of the strip images in video real time.
Abstract:
A relatively simple interferometric method for the absolute testing of plane surfaces is disclosed, along with special apparatus for carrying out the inventive method. Two plane surfaces to be tested (A.sub.6,B.sub.6) are inserted simultaneously into the interferometer's measuring-beam path so that the measuring beam is reflected from each plane surface at two respective and different incident angles (.alpha., .beta.). During successive steps, the plane surfaces (A.sub.6,B.sub.6) are angularly repositioned and shifted so that at least one of the incident angles (.alpha., .beta.) is changed. Interferograms are recorded during each step and analyzed mathematically.
Abstract:
The injection current for a laser diode is modulated so that a pregiven coherence function is obtained which drops off continuously at both ends outside of the coherence length. Several laser diodes are used for a very short coherence length for which the modulated wave numbers of the emitted radiation follow one another or overlap.
Abstract:
Interferometric scanning method(s) and apparatus for measuring rotationally and non-rotationally symmetric test optics either having aspherical surfaces or that produce aspherical wavefronts. A spherical or partial spherical wavefront is generated from a known location along a scanning axis though the use of a decollimator carrying a spherical reference surface. The test optic is aligned with respect to the scanning axis and selectively moved along it relative to the known origin so that the spherical wavefront intersects the test optic at the apex of the aspherical surface and at radial zones where the spherical wavefront and the aspheric surface possess common tangents. The test surface is imaged onto a space resolving detector to form interferograms containing phase information about the differences in optical path length between the spherical reference surface and the test surface while the axial distance, v, by which said test optic moves relative to said spherical reference surface is interferometrically measured. Based on an analysis of the phase information contained in the interferograms and the axial distance, v, the deviation in the shape of the aspheric surface from its design in a direction normal to the aspheric surface is determined. In scanning, two cameras having different magnification are preferably used simultaneously with the one of higher magnification observing near the part axis where high fringe densities occur while that of lower magnification observes the full part surface. Special procedures are described for alternately improving accuracy near the axis.
Abstract:
Interferometric apparatus and methodology for precisely measuring the shape of rotationally and non-rotationally symmetric optical surfaces comprising an illumination source with two wavelengths, a transmission flat with a reference surface, a basic optical system for producing a wavefront of predetermined shape, a compensation component having an aspheric wavefront shaping surface and an aspheric reference surface. The aspheric shaping surface modifies the predetermined wavefront so that it impinges on the aspheric reference surface with a shape substantially that same as that of aspheric reference surface. For a given aspheric reference surface, the radius or curvature and spacing of the aspheric shaping surface are optimized so that its aspheric departure is no larger than that of the aspheric reference surface. Precise alignment in six degrees of freedom is provided via feedback control.