Hughes Aircraft Company

Phillip V Mitchell

Thomas R O'Meara

David M Pepper

Gilmore Joseph Dunning

Marvin B Klein

Stephen W McCahon

An ultrasound detection system that is relatively insensitive to rough workpiece surfaces, suppresses low frequency noise, and provides high sensitivity without the need for active stabilization. An optical probe beam is reflected and phase modulated by a workpiece surface that is being vibrated by ultrasound. A time-delay interferometer optically interferes the phase modulated probe beam with a time-delayed replica of itself. The optical interference generates optical interference fringes that move in accordance with the workpiece surface velocity. The interference fringes are detected by a non-steady-state photo-electromotive-force (NSS-photo-EMF) detector that generates an output signal when the frequency of fringe motion exceeds a predetermined threshold.

System and method for detecting ultrasound using time-delay

A laser-ultrasonic inspection system is provided for on-line and off-line inspection of a workpiece. The system utilizes an optical acoustic wave generation and detection system with relatively high spatial resolution and which appreciably reduces the effects of parasitic acoustic coupling. An array of acoustic waves are generated in the workpiece by a short pulse optical transmitter bee with a beam geometry that is tailored to focus the acoustic waves at an inspection site in the workpiece. The acoustic waves that probe the inspection site are then detected by reflecting an optical read-out beam from a surface of the workpiece and optically interfering it with an optical reference beam. The geometry of the optical read-out beam is chosen such that the read-out beam only detects the acoustic waves that arrive from the inspection site (acoustic waves that arrive from other parasitic acoustic sources are out of phase with respect to each other and cancel out). A wavefront compensation system improves acoustic clutter rejection and also improves the signal-to-noise by compensating for phase and amplitude aberrations induced on the optical read-out beam by the optically rough surface of the workpiece.

Laser-ultrasonic non-destructive, non-contacting inspection system

An optical self-referencing ultrasonic receiver for detecting ultrasonic waves removes wavefront distortions imparted on the optical beams by diffusely reflecting readout surfaces or other sources, compensates for noise induced phase errors on the readout beam, compensates for amplitude noise present on the readout beam, substantially matches the wavefronts of the readout and reference beams, is capable of operating in a heterodyne mode and is self-aligning. In one embodiment, ultrasonic waves are measured by directing a signal beam and a reference beam to a surface of the workpiece so that the signal beam reflects off an area that is being vibrated by the ultrasonic waves, and the reference beam reflects off a different area of the surface. The signal beam gets phase modulated by the ultrasonic wave induced vibrations and also by other noise induced vibrations. The reference beam only gets phase modulated by the noise induced vibrations. The phase modulated signal and reference beams are directed to a wavefront compensator that overlaps the beams, substantially matches their wavefronts and removes wavefront distortions without altering their respective optical phases. The wavefront compensated beams are directed to a coherent detector whose output signal has a phase shift which corresponds to the difference between the optical phase shift on the signal beam (due to ultrasonic wave vibrations and noise vibrations) and the optical phase shift on the reference beam (due to noise vibrations only). Thus, noise induce vibrations common to both beams are canceled out.

Self-referencing laser-based ultrasonic wave receiver

A spatial light modulator that is particularly suited for adaptive optics systems includes a charge transfer plate in which accumulated charge is continuously drained from the charge transfer pins, allowing the modulator to be operated in a continuous mode with a very rapid speed of response. Charge is drained through RC circuits that consist of inherent or discrete resistors and inherent capacitances associated with the pins. A lenslet array focuses an input beam onto the curvature bases of pixels in an associated deformable mirror, thereby obtaining reflections from the mirror with generally flat wavefronts and a greatly increased optical efficiency; a companion lenslet array and mirror combination outside the SLM compensates pixel inversions produced by the first lenslet array. The charge transfer plate is made gas impervious by fabricating the charge transfer pins as thermally migrated conductors, and conductive electric shield pins are preferably also provided to shield the charge transfer pins from each other.

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Simi Valley, CA, United States of America

Phillip V Mitchell