I-Tek, Inc.

United States of America as Represented by the Secretary of the Air Force

Alan J MacGovern

Richard A Hutchin

Bruce A Horwitz

Robert A Sprague

Richard H Howell

A shearing interferometer produces a matrix of loops of wavefront phase difference vector signals derived from the interferogram indicative of wavefront slopes, where each loop corresponds to a sub-aperture portion of the wavefront under examination. Curl operators are applied to sum the vector signals in one direction about the loops to provide sums which are set equal adjacent loops are identified having such modified sums differing from each other by at least one integer, and in certain cases having modified sums of integers of opposite sign indicative of phase difference measurements greater than the dynamic range of the interferometer, and thus having error components therein. The phase difference values at the boundary of each of such particular identified adjacent loops are operated upon to set the modified sums to zero, to in turn eliminate the error components due to operation of the interferometer outside of the limited dynamic range. Particular edge loops are also identified at the outer edges of the matrix having a positive or negative modified sum, and also having all three loops bounding the particular loops having modified sums of zero. The edge position phase difference values are modified in one or more steps, until the positive or negative modified sums of the particular edge loop are reduced to zero. Eight algorithms for executing the above stated functions are setforth herein.

Spatial processing for single or dual shear wavefront sensor

An improved shearing interferometer is provided having an acousto-optic cell wherein two sets of orthogonal diffraction gratings are formed therein by applying two electrical signals thereto having different frequencies. A wavefront to be examined is passed through the cell, and both signal frequencies applied to the cell are varied to cause the resulting shearing interferogram to be sequentially directed at a pair of orthogonal linear photodetector arrays. The degree of shear may be readily adjusted by changing the difference between the frequencies of the two signals applied to the cell.

Shearing interferometer employing an acousto-optic cell

A process and apparatus are disclosed for aligning a laser beam from a laser transmitter with an incoming laser beam, and driving any sensed tilt differences on an aperture and subaperture basis to zero. The apparatus uses a shared aperture component to sample the outgoing laser beam and the incoming target beam, a retroreflector array to reverse the direction of the subaperture samples of the outgoing beam, a common-mode wavefront sensor to measure subaperture tilt differences between the reversed samples of the laser and the incoming target beam, and a deformable mirror to drive any sensed tilt differences to zero. A transparent beamsplitter is used as the shared aperture component and an AC shearing interferometer is used as the basis for the common-mode sensing. By forcing the outgoing beam to be then conjugate of the incoming beam it is automatically precompensated for any aberrations in the transmission path.

Discrete phase conjugate technique for precompensation of laser beams

A wavefront sensor employs a novel DC shearing interferometer which produces four interferograms which are 90.degree. phase shifted with respect to each other. The incoming wavefront is replicated into two beams, a portion of each being reflected off of a beamsplitter and the remaining portion being transmitted therethrough, at first and second portions of the beamsplitter. After leaving the beamsplitter the transmitted and reflected beams are reflected back 180.degree. by a pair of retroreflectors, and directed at third and fourth portions of the beamsplitter. The retroreflectors are adjusted to produce four shearing interferograms and a quarter wave plate is positioned in the path of one of the beams to cause the four interferograms to have a 90.degree. phase shifted relationship with respect to each other. The interferograms are thereafter projected upon intensified self scanning diode arrays, which digitize the interference patterns for convenient processing by means of a four-bin algorithm, which in turn generates estimated phase data indicative of the shape of the wavefront in a given direction. The process may be duplicated to produce second measurements in an orthogonal direction, which enables the mapping of the wavefront in both X and Y. In contrast with A.C. shearing interferometers, the wavefront shapes of very brief plused beams of light may be measured.

Wavefront sensor employing novel D.C. shearing interferometer

Apparatus for recording a serial line of electrical data as a spatial array of optical data. The apparatus employs an acousto-optic device through which the electrical signal to be recorded is passed as a continuous acoustic wave. The device is illuminated by a laser and imaged onto a recording medium to form an image of the acoustic wave passing through the device. By pulsing the laser just as the acoustic wave fills the device, a line of optical data can be recorded which will correspond to the acoustic wave in the device. By indexing the recording medium and reimaging every time a new acoustic wave just fills the device, an entire raster may be recorded.

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Acton, MA, United States of America

Alan J MacGovern