Wyko, Inc.

Chiayu Ai

James C Wyant

Robert E Parks

John B Hayes

Paul J Caber

Joseph A Lamb

Yiping Xu

Erik L Novak

Lian-Zhen Shao

An interferometer mounting mechanism that consists of a horizontal shaft rigidly connected to the interferometer in axial alignment with the optical path of the instrument and protruding through an opening in the center of the transmission flat. A sample stage adapted to receive a computer-drive disk is attached to the distal end of the shaft, so that the stage is directly and rigidly connected to the interferometer. The sample stage consists of a hub capable of retaining a disk in precise alignment with the transmission flat by hanging its center hole on two support posts and resting the disk on three pressure tips on the hub. A system of push-pull adjustment screws is provided to set the proper tip/tilt of the disk.

Coaxial disc-mount for measuring flatness of computer-drive discs by

A broad-bandwidth interferometric system that produces irradiance signals at multiple vertical-scanning positions as a function of optical path differences between a test and a reference surface. The effective peak of the envelope defined by the modulation component of the irradiance signal is estimated by finding the scanning position corresponding to the centroid of a function substantially equal to the square of the first-order derivative of the measured irradiance. The surface height at each pixel is determined directly from digital irradiance signals, thereby greatly reducing the data-processing steps and associated costs taught by the prior art and correspondingly simplifying the hardware requirements of the system for rapid on-line display of height measurements. The approach is free of the ambiguities inherent in multi-peak modulation functions, thereby producing surface maps with reduced artifacts. This improved technique produces results otherwise comparable with those obtained by standard techniques and requires no dedicated hardware for rapid on-line applications.

Centroid approach for estimating modulation peak in broad-bandwidth

A method and apparatus for measuring an absolute profile of a flat using an interferometer system that includes an interferometer adapted to support two flats, a detection system, and a computer adapted to compute the OPD (optical path difference) between surface of the two flats, wherein a first flat A! having a first surface and a second flat B! having a second surface are supported in the interferometer, with the second surface facing the first surface. The interferometer system measures the OPDs between the first and second surfaces for each pixel. The first flat A! then is rotated by a number of predetermined angles relative to its initial position and each time the OPDs are measured. The first flat A! is rotated to its initial position or 180.degree. therefrom. A third flat C! having a third surface is substituted for the second flat. The OPDs between the first and third surfaces are measured. The first flat A! is replaced by the second flat, with the second surface facing the third in an orientation mirror imaged to its original orientation. The interferometer system is operated to measure the OPDs. The computer solves first, second, and third equations to obtain the entire surface topographies of the first, second, and third surface, wherein each equation is expressed as a sum of even--even, even-odd, odd-even, and odd--odd parts so as to effectuate cancellation of terms, permitting solving of the equations for the surface topography.

Method and apparatus for absolute optical measurement of entire surfaces

Interferometric apparatus that combines white-light VSI and single-wavelength PSI capabilities to improve the accuracy of height measurements in steep regions and in areas with large inter-pixel steps on the test surface. The technique consists of performing VSI measurements to obtain a relatively coarse profile of the test surface and to identify regions separated by a large step. Then PSI measurements are carried out over the test surface to obtain a relatively fine profile. Offsets between VSI and PSI measurements are calculated to correct for misalignments and phase shifts that may have occurred between the two sets of measurements. Finally, the fine PSI data are integrated to within one quarter wavelength of the coarse VSI data. The resulting quality of the height data in each of the step regions is thus improved to within the resolution of the PSI measurements.

Combination of white-light scanning and phase-shifting interferometry

Fizeau interferometer that utilizes a multimode laser as a light source for testing transparent thin-plate samples. As a result of multimode linear laser operation, interference fringes are obtained only when the optical path difference between the reference surface and test surface is equal to twice a multiple of the laser's effective cavity length. By judicially selecting the multimode spectrum of operation and the effective cavity length of the laser, the interferometer may be calibrated to produce interference fringes at a workable separation between the reference and test surfaces without ghost interference fringes from the far surface of the thin-plate sample. Another embodiment of the invention alternatively utilizes two linear lasers with different effective cavity lengths to eliminate ghost interference fringes when the optical thickness of the thin-plate is equal to a multiple of one laser's effective cavity length.

Multimode-laser interferometric apparatus for eliminating background

The invention provides a technique for eliminating 'ripple' or ghost fringes from a wavefront transmitted by an optical window with a very small wedge angle, distortions in the wavefront being measured by an interferometer. A collimated beam produced by the interferometer is transmitted through the optical window, which is tilted so as to prevent direct reflections from entering a detector of the interferometer. The beam transmitted through the window is reflected by a return flat back through the window and transmitted to the detector. The return flat is tilted slightly in the direction of or opposite to the direction of tilt of the window, causing the re-incident angle of the returned ray to be different from the original incident angle of the collimated beam. This causes the multiple reflections within the window to be different and to be out of phase. The ghost fringes are cancelled by appropriately tilting the return flat.

Method for testing an optical window with a small wedge angle

A method and system are described for performing phase unwrapping integrations in a phase-shifting interferometric profiling operation. The disclosed technique uses one characteristic of modulation or slope distributions to segment the modulation or slope histogram into a plurality of sections. The principal phase values are divided into a plurality of groups in accordance with corresponding modulation or slope histogram sections. The phase unwrapping integrations are performed in such an order that the areas with a high probability of containing a 2.pi. discontinuity are contained in the last group integrated. Thus, inaccuracies due to 2.pi. discontinuities do not 'propagate' to earlier-computed phase values computed by the phase unwrapping algorithm.

Interferometric integration technique and apparatus to confine 2.pi.

A method and apparatus is disclosed for aligning a reflective surface with an alignment axis in a representative environment of an interferometer. An image of the reflective surface is focused onto a diffuse screen to form a spot image thereon. Rays of the spot image emanating from the diffuse screen are collimated. Some of the collimated rays are focused onto a detector to form a non-inverted image spot. A portion of the collimated rays are intercepted and inverted by means of an image inverter aligned with the alignment axis. The inverted rays are focused onto the detector to form an inverted image spot. The reflecting surface is moved so as to cause the inverted image spot and the non-inverted image spot to coincide, at which point the reflecting surface is aligned with the alignment axis.

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Tucson, AZ, United States of America

Chiayu Ai