Abstract: A laser ultrasonic inspection apparatus and method which enables remote sensing of thickness, hardness, temperature and/or internal defect detection is disclosed. A laser generator impinges a workpiece with light for generating a thermo-elastic acoustic reaction in a workpiece. A probe laser impinges the workpiece with an annularly-shaped probe light for interaction with the acoustic signal in the workpiece resulting in a modulated return beam. A photodetector having a sensitive region for detecting an annularly-shaped fringe pattern generated by an interaction of a reference signal and with the modulated return beam at said sensitive region.

Abstract: A lens for angularly overlapping a central portion of an optical beam with an outer portion of the beam is disclosed. The lens comprises a lens body having an optical axis, a rear surface on said lens body for receiving an optical beam, and a front surface on said lens body that includes inner and outer portions. The outer surface portion is inclined at a greater angle from the optical axis than the inner surface portion so that the outer portion of a beam transmitted through the lens from its rear surface to said outer surface portion is refracted by a lesser angle than an inner portion of the beam which reaches said inner surface portion.

Abstract: A contactless system for imaging an acoustic source within a workpiece directs a preferably annular optical probe beam pattern onto the vibrating workpiece surface, with the vibrationally modulated beam then detected by an array of preferably non-steady-state photo-emf detectors arranged in a similar pattern. The probe beam is scanned over the vibrating surface, either mechanically or through an electronically simulated phased array scheme. Time gating is used to suppress unwanted side-lobes when the individual detector outputs are summed over an appreciable waveband. A self-calibration scheme is also preferably used that provides a quantitative as well as qualitative output. A calibration modulation is imposed on at least one of the probe and reference beams, with the calibration modulation later removed at a post-detector stage and used to normalize the acoustic modulation output.

Abstract: A contactless system for imaging an acoustic source within a workpiece directs a preferably annular optical probe beam pattern onto the vibrating workpiece surface, with the vibrationally modulated beam then detected by an array of preferably non-steady-state photo-emf detectors arranged in a similar pattern. The probe beam is scanned over the vibrating surface, either mechanically or through an electronically simulated phased array scheme. Time gating is used to suppress unwanted side-lobes when the individual detector outputs are summed over an appreciable waveband. A self-calibration scheme is also preferably used that provides a quantitative as well as qualitative output. A calibration modulation is imposed on at least one of the probe and reference beams, with the calibration modulation later removed at a post-detector stage and used to normalize the acoustic modulation output.

Abstract: A dual time delay interferometer (TDI) enables remote sensing of phase modulated information, such as the detection of ultrasonic vibrations from highly diffuse surfaces, preferably in the range from about 10 kHz to 100 MHZ or more. The system can also be configured in a transceive mode with a dual pass through a single TDI, which is well suited to optical communications. A non-steady-state photo-electromotive-force detector tracks the movement of interference fringes (whose position shifts as the surface vibrates), rather than their absolute position. A phased array of the sensors can be used for enhanced imaging applications requiring better signal/noise ratios, or alternatively, when lower power optical sources are employed.

Abstract: An optical amplification system directs a diffraction-limited signal beam through a series of approximately 90.degree. crossings with a number of non-diffraction-limited pump beams in a photorefractive medium. All of the beams are s-polarized, resulting in an energy transfer from the pumps to the signal beam while leaving the signal beam diffraction-limited. The photorefractive medium is preferably a series of BaTiO.sub.3 :Rh crystals that receive the pump and signal beams through orthogonal faces, with their C-axes at approximately 45.degree. to both beams. A binary tree optical distribution network is used to minimize waveguide splits in forming a large number of pump beams.

Abstract: 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.

Abstract: 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).

Abstract: 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.

Abstract: A multilayer stack of alternating low index and high index of refraction low loss dielectric mirror layers are formed on top of a metallic mirror surface, the thicknesses of the mirror layers being chosen to satisfy the Bragg condition at a selected incident angle of polarized light. The dielectric layer adjacent the metallic reflective mirror substrate can have a thickness which produces circularly polarized light exiting the apparatus. An electro-optical layer of EO material can be substituted for the dielectric layer adjacent the metallic mirror and a controlled elliptically polarized output can be produced by altering the electric field applied across the EO layer. This device can be used as a very high power high speed EO modulator.

Abstract: 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.

Abstract: An optical beam scanner incorporating an array of beam deflection elements commonly controlled to steer an optical beam impingent on the array is described. The beam steering elements are arranged in the array as individually controlled elements and the deflection of the beam is accomplished by setting the phase tilt and the phase offset of each element according to a calculation which removes modulo 2.pi. phase shift from the required position relative to a flat plane. Thus, the array elements can be thin and need only supply about 2 radians of phase shift. These elements may be incorporated in a planar array using beam deflection elements such as liquid crystal beam deflectors by choosing a drive scheme representing either a blazed array or a flat piston array.

Abstract: A master oscillator power amplifier (MOPA) system which isolates the master oscillator (MO) from the return amplified beam by dividing the return beam into two components, introducing a phase shift between the components, and recombining the phase shifted beam components through constructive interference into an output beam directed away from the MO. A destructive interference return output is directed back towards the MO, but is held to a negligible level by making the phase shift approximately equal to an odd number of half-wavelengths at the return beam wavelength. In the preferred embodiment a stimulated Brillouin scattering phase conjugate mirror (PCM) is used to direct the amplified beam for a second amplification pass, while a Mach-Zender interferometer transmits the beam both before and after double amplification.

Abstract: Apparatus for selectively limiting the response of an auxiliary liquid crystal light valve which is used in a dual liquid crystal light valve laser optics system for correcting inherent liquid crystal light valve distortion by isolating an atmospheric reference beam from the main laser beam in the auxiliary correction system. Two types of isolation are provided: dual bandwith and dual polarization. In the former, the response bandwidth of the auxiliary liquid crystal light valve is shifted to prevent overlap with the bandwidth of an atmospheric reference wavefront. In the dual polarization form of isolation, provision is made for rotating the polarization of only one of the two interacting beams.

Abstract: An integrated adaptive optics apparatus for processing wavefront errors. In a preferred embodiment, a modified liquid crystal light valve (LCLV) is used as an integrated wavefront sensing and wavefront control system. A remote reference aberrated wavefront 10, passed through the liquid crystal layer and reflected, is then fed-back in part to the rear surface of the liquid crystal light valve 12, after combination with a local reference plane wave 16. The resulting interference pattern is incident on the photosensitive layer 26 of the LCLV, causes commensurate index changes in the liquid crystal layer, and adapts the LCLV for performing aberration correction. In an alternative embodiment, a second laser beam 11 may be predistorted by passing it through the adapted liquid crystal layer in order to compensate in advance for atmospheric path disturbances. The present invention provides an adaptive optics correction system having high spatial resolution.

Abstract: A self-referencing target imaging system 10 capable of long range imaging at visible wavelengths is disclosed herein. The imaging system 10 of the present invention includes a transmitter 20 for illuminating a target 30 with a series of electromagnetic pulses P. The present invention further includes an apparatus 35, 40 and 45 for redirecting first R1 and second R2 reflections of each illuminating pulse P from first 32 and second 34 portions of the target 30, respectively. A frequency modulator 50 driven by a generator 55 shifts the frequency of each first reflection R1 to produce a reference reflection R1' corresponding to each illuminating pulse P. The present invention further includes an arrangement of reflective elements 60 and 65 for respectively combining the reference R1' and the second R2 reflections of each illuminating pulse P to generate a series of combined reflections. A detector 70 generates an imaging signal in response to the series of respectively combined reflections.

Abstract: A cascaded adaptive optics system for correction of aberrations in a light beam. The system includes a plurality of spatial light modulators (SLMs) in a cascaded arrangement to provide an adaptive optics system characterized by wide range, rapid response, and high resolution. The spatial light modulators may be identical or have characteristics that are complementary in providing a combined output that advantageously corrects for aberrations. A conventional adaptive optics system such as a deformable mirror may be used as one or more of the SLMKs. Liquid crystal light valves (LCLVs) may be advantageously used as one or more of the SLMs in the invention. A single LCLV may be cascaded with itself in a multiple-pass configuration by means of suitable reflectors.

Abstract: Apparatus for compensating for inherent distortions in a modified liquid crystal light valve used in an integrated wavefront sensing and wavefront control system for laser optics. A main wavefront sensing and control system utilizes a liquid crystal light valve selected for response speed but having inherent surface non-linearities. A beam from an auxiliary laser is intermittently applied, while the main laser is blocked, to both the fast response LCLV of the main system and to a slower response LCLV of an associated correction system. The second LCLV system corrects for the non-linearities in the surface of the first LCLV and then maintains the stored correction signal for a decay interval which corresponds to several response times of the main LCLV, thus permitting the main LCLV system to perform fast correction of atmospheric aberrations in the laser beam wavefront unaffected by inherent surface non-linearities.

Abstract: An adaptive optics system is disclosed which has a phase detector to detect phase distortions acquired by an input beam, and a separate phase adjustor which predistorts a transmission beam so that it is restored to its proper phase during transmission back through the same medium travelled by the input beam. The phase adjustor consists of a liquid crystal mechanism with an area substantially greater than that of the phase detector, thereby permitting high power operation. Liquid crystal pixels in the phase adjustor have dual transistor signal storage circuits which apply operating signals to the pixels without significant decay or flicker. The phase adjustor can be constructed in either a reflective or transmissive mode. Two phase adjustors may be placed in series to enhance response time and/or process an unpolarized beam. A data processor interfaces between the phase detector and phase adjustor.

Abstract: An optical beam scanner incorporating an array of beam deflection elements commonly controlled to steer an optical beam impingent on the array is described. The beam steering elements are arranged in the array as individually controlled elements and the deflection of the beam is accomplished by setting the phase tilt and the phase offset of each element according to a calculation which removes modulo 2.pi. phase shift from the required position relative to a flat plane. Thus, the array elements can be thin and need only supply about 2 radians of phase shift. These elements may be incorporated in a planar array using beam deflection elements such as liquid crystal beam deflectors by choosing a drive scheme representing either a blazed array or a flat piston array.