The Boeing Company

Zygo Corporation

Peter J deGroot

Barbara A Capron

John A Bell

William D Sherman

Paul Frederic Sjoholm

John A McGarvey

Ronald L Hagman

W Randall Babbitt

A computer-based stroboscopic interferometric microscope system for measuring the topography of a microscopic vibratory object includes an interferometric microscope equipped with a multiple-color (e.g., LED) or white-light source, a mechanical scanning apparatus for varying the optical path difference between the vibratory object and a reference surface, a camera having a two-dimensional detector array, and digital signal processing apparatus for determining surface height from interference data. Interferograms for each of the detector image points in the field of view are generated simultaneously by scanning the object in a direction approximately perpendicular to the object surface illuminated stroboscopically while recording detector data in digital memory. Recorded interferograms for each image point are then transformed into the spatial frequency domain by Fourier analysis, and the surface height for each corresponding object surface point is obtained by examination of the complex phase as a function of spatial frequency. A complete three-dimensional image of the object surface is then constructed from the height data and corresponding image plane coordinates. The three-dimensional image may be presented on a display or hard copy or written to a storage medium.

Stroboscopic interferometry with frequency domain analysis

The invention performs coordinate measurement employing multiple-frequency intensity-modulated laser radar. A laser diode source is intensity modulated by variation of its excitation current. Its output beam is directed to a target using scanning mirrors or other opto-mechanical means, and the light returned from the target is detected. The modulation frequency is alternated between two or more values, creating a dataset of several relative phase measurements that uniquely determine the distance to the target without ambiguity. A device for carrying out such a method includes a laser whose output is modulated by a high frequency signal generator, optics for directing the output signal to the target to a detector, a signal generator which generates reference signals offset in frequency from the intensity modulation frequencies by a predetermined amount; mixers for combining the return signals with the reference signals to form a first set of intermediate frequency signals, and for combining the modulation signals with the reference signals to form a second set of intermediate frequency signals, and a computer which calculates phase differences between the output beam and the return signals for each modulation frequency from the intermediate frequencies, and determines the distance to the target from the phase differences.

Method and apparatus for measuring distance to a target

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Middletown, CT, United States of America

Peter J deGroot