4d Technology Corporation

Onto Innovation Inc.

Ad Technology Corporation

Neal Brock

James E Millerd

Erik Novak

James C Wyant

Brad Kimbrough

John Hayes

Goldie Goldstein

Larry Denneau, Jr

A pixelated color mask is combined with a pixelated polarization mask in dynamic interferometry. The color mask includes a wavelength-selective bandpass filter placed in front of each camera pixel such that each set of contiguous four camera pixels is covered by two green bandpass filters, a red bandpass filter, and a blue bandpass filter. The pixelated phase mask is coupled to the color filters such that one polarization filter covers one set of color filters. At least three polarization filters are used to calculate phase. In addition, the color signals can be used, for example, to encode the motion of the interferometer, to provide very high speed autofocus or tip/tilt feedback, to create a color image of the object being measured, to automatically focus the system at different positions for different measurements conducted with different color sources, and to perform heterodyne interferometry with a single, vibration-immune measurement.

Interferometry with pixelated color discriminating elements combined with pixelated polarization masks

A cycloidal diffraction waveplate is combined with a pixelated phase mask (PPM) sensor in a dynamic fringe-projection interferometer to obtain phase-shifted interferograms in a single snap-shot camera operation that provides the phase information required to measure test surfaces with micrometer precision. Such mode of operation enables a portable embodiment for use in environments subject to vibration. A shifting mechanism coupled to the cycloidal waveplate allows temporal out-of-phase measurements used to remove noise due to test-surface characteristics. Two or more pixels of each unit cell of the PPM are combined to create super-pixels where the sum of the phases of the pixels is a multiple of 180 degrees, so that fringes are eliminated to facilitate operator focusing. By assigning colors or cross-hatch patterns to different ranges of modulation measured at the detector, the areas of best focus within the field of view are identified quantitatively to ensure measurements under best-focus conditions.

Single snap-shot fringe projection system

A phase-difference sensor measures the spatially resolved difference in phase between orthogonally polarized reference and test wavefronts. The sensor is constructed as a pixelated phase-mask aligned to and imaged on a pixelated detector array. Each adjacent pixel of the phase-mask measures a predetermined relative phase shift between the orthogonally polarized reference and test beams. Thus, multiple phase-shifted interferograms can be synthesized at the same time by combining pixels with identical phase-shifts. The multiple phase-shifted interferograms can be combined to calculate standard parameters such as modulation index or average phase step. Any configuration of interferometer that produces orthogonally polarized reference and object beams may be combined with the phase-difference sensor of the invention to provide, single-shot, simultaneous phase-shifting measurements.

Pixelated phase-mask interferometer

A multi-channel imaging system is calibrated by measuring the geometric distortion in each sub-image, generating corresponding correction factors, and applying such factors to correct subsequent image data. In addition, intensity transfer-function arrays are measured at each pixel, and further used to correct for system and detector nonlinearities and nonuniformity between images. The procedure is repeated over a range of wavelengths to produce a complete set of correction coefficients and transfer functions. When the system is used for interferometric phase measurements, multiple measurements are preferably taken and a random phase offset in the reference path length is introduced at each measurement. The multiple phase data so derived are then averaged to reduce phase-dependent systematic measurement errors.

Calibration and error correction in multi-channel imaging

A polarizing point-diffraction plate is used to produce common-path test and reference wavefronts with mutually orthogonal polarizations from an input wavefront. The common-path test and reference wavefronts are collimated, phase shifted and interfered, and the resulting interferograms are imaged on a detector. The interference patterns are then processed using conventional algorithms to characterize the input light wavefront.

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Tucson, AZ, United States of America

Neal Brock