Abstract: A method and apparatus for a photoinduced electromotive force sensor. The sensor has an active substrate formed of a semi-insulating photoconductor with sufficient carrier trap density to form an effective charge grating and pairs of electrodes disposed on the active substrate, where the sensor is configured to reduce the photovoltaic effect caused by the incident light in the vicinity of the electrodes. The shape or composition of the electrodes may be selected to reduce the photovoltaic effect or the electrodes may be disposed on the substrate to average out the photovoltaic effect arising from each one of the electrodes.

Abstract: A method and apparatus for a photoinduced electromotive force sensor. The sensor has an active substrate formed of a semi-insulating photoconductor with sufficient carrier trap density to form an effective charge grating and pairs of electrodes disposed on the active substrate, where the sensor is configured to reduce the photovoltaic effect caused by the incident light in the vicinity of the electrodes. The shape or composition of the electrodes may be selected to reduce the photovoltaic effect or the electrodes may be disposed on the substrate to average out the photovoltaic effect arising from each one of the electrodes.

Abstract: An apparatus is provided for detecting flaws in a threaded bore having at least one thread with a helical root is provided. The apparatus may include a thread engagement member configured to engage the at least one thread of the threaded bore. The apparatus may also include a probe coupled with the thread engagement member. The probe may be configured to direct light onto the helical root of the threaded bore. The probe and the thread engagement member may be adapted to rotate relative to the bore while the probe continually directs light onto the helical thread so that the light sweeps along a section of the helical root.

Abstract: Longitudinal and shear ultrasonic waves are generated inside a material by irradiating a laser beam onto a first surface, e.g., incident surface, of the material. An ultrasonic longitudinal wave and a mode converted wave reflected by a second surface, e.g., a bottom surface, of the material are detected, and times of flight of the ultrasonic longitudinal wave and the mode converted wave are measured. A thickness of the material is measured based on the times of flight and a correlation, obtained in advance, between longitudinal and shear wave velocities of the material and temperature of the material.

Abstract: A photo-EMF sensor and a method of making same has a substrate with a semiconducting layer; a plurality of sensing regions in the layer, each sensing region including (i) a pair of electrodes disposed in, on or above the layer and (ii) an active region in the layer disposed adjacent said pair of electrodes; and a plurality of inactive regions in said the arranged between adjacent sensing regions. The inactive regions and the sensing regions are dosed with a desensitizing agent, the inactive regions receiving a relatively higher dose of the desensitizing agent and the sensing regions receiving a relatively lower dose of the desensitizing agent. The active layer is preferably placed in a monolithic Fabry-Perot cavity to enhance the optical efficiency and performance of the sensor.

Abstract: Longitudinal and shear ultrasonic waves are generated inside a material by irradiating a laser beam onto a first surface, e.g., incident surface, of the material. An ultrasonic longitudinal wave and a mode converted wave reflected by a second surface, e.g., a bottom surface, of the material are detected, and times of flight of the ultrasonic longitudinal wave and the mode converted wave are measured. A thickness of the material is measured based on the times of flight and a correlation, obtained in advance, between longitudinal and shear wave velocities of the material and temperature of the material.

Abstract: A photo-EMF sensor and a method of making same has a substrate with a semiconducting layer; a plurality of sensing regions in the layer, each sensing region including (i) a pair of electrodes disposed in, on or above the layer and (ii) an active region in the layer disposed adjacent said pair of electrodes; and a plurality of inactive regions in said the arranged between adjacent sensing regions. The inactive regions and the sensing regions are dosed with a desensitizing agent, the inactive regions receiving a relatively higher dose of the desensitizing agent and the sensing regions receiving a relatively lower dose of the desensitizing agent. The active layer is preferably placed in a monolithic Fabry-Perot cavity to enhance the optical efficiency and performance of the sensor.

Abstract: A laser-based technique to determine glass thickness employs a pulsed laser to induce an ultrasonic wave between the surfaces of a region of glass, causing the surfaces to move in and out at a characteristic frequency. The surface motion is monitored to determine the characteristic frequency, which is proportional to the thickness of the glass in the region of the ultrasonic wave. The pulsed laser produces a short duration pulse that illuminates a surface of the glass, which is absorbed within the glass to cause a rapid thermal expansion that generates the ultrasonic wave. The surface motion induced by the ultrasonic wave is preferably detected with a laser interferometer system, the output of which is analyzed to determine the surface motion's characteristic frequency.

Abstract: A photo-EMF detector for the collection of photons includes a substrate formed of a photorefractive semiconductor and a plurality of interlaced electrode pairs disposed over the substrate. Each electrode pair includes two parallel electrodes defining an active area therebetween for the collection of photons. One electrode of each pair is disposed between an adjacent pair of electrodes and proximate one electrode of the adjacent pair, light from striking a substrate surface between proximate electrodes and outputs from each of the plurality of interlaced electrode pairs are collected.

Abstract: Faults, dimensions and other characteristics of a material or structure are sensed by a coherent beam's reflection from the material during ultrasonic or very fast vibration. The reflected beam acquires a phase substantially different from its original phase and from the phase of a reference beam split from the common source beam. The reflected beam and the reference beam are superimposed by diffraction in a photorefractive polymer composite adaptive holographic beamsplitter, and the superimposed beams are detected by a photodetector capable of detecting small interference changes from ultrasonic surface displacements or perturbations. An apparatus and method defining an improved homodyne interferometer for performing the method is described.

Abstract: Single-beam laser apparatus for measuring surface velocity at acoustic frequencies and surface displacement at ultrasonic frequencies includes a source laser and optics for directing a single laser beam at normal incidence to a surface. A photo EMF detector and optics are provided for directing surface reflected laser beam at the photo EMF detector in order to provide outputs therefrom which are directly proportional to all three orthogonal components surface velocity or displacement.

Abstract: Faults, dimensions and other characteristics of a material or structure are sensed by a coherent beam's reflection from the material during ultrasonic or very fast vibration. The reflected beam acquires a phase substantially different from its original phase and from the phase of a reference beam split from the common source beam. The reflected beam and the reference beam are superimposed by diffraction in a multiple quantum well adaptive holographic beamsplitter, and the superimposed beams are detected by a photodetector capable of detecting small interference changes from ultrasonic surface displacements or perturbations. An apparatus and method defining an improved homodyne interferometer for performing the method is described.

Abstract: A new photorefractive material comprises BaTiO.sub.3 double-doped with two dopant species, both of which have at least two valence states, with one of the dopant species (e.g., cerium) having an ionization level that is near the middle of the barium titanate bandgap and the other dopant species (e.g., rhodium) having an ionization level that is closer to the valence band edge of barium titanate, such that both dopant species are sensitive to visible light, but only one dopant species (the one closer to the valence band edge) is sensitive to infrared radiation. The double-doped BaTiO.sub.3 provides a unique combination of photorefractive properties, thereby improving its performance as a holographic storage medium. The double-doped barium titanate crystal is employed as a holographic recording element. The double-doped barium titanate crystal has a dark storage time at room temperature of several years or more and may be nondestructively read out at an infrared wavelength.

Abstract: An optical amplification system directs a diffraction-limited signal beam through a series of crossings, at substantially less than 90.degree. crossing angles, with a number of non-diffraction-limited pump beams in a photorefractive medium. The pump beams are e-polarized while the signal beam travels down the crystal medium's c-axis and is polarized in the same plane as the pump beam polarization, 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 are aligned parallel to the angled edge of a wedged-shape prism through which the pump beams are transmitted, with the crystals cut so that their C-axes are parallel to the signal beam.

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 improved process is provided for making optical limiters having a graded axial distribution of a reverse saturable absorber compound, such as a buckminsterfullerene, in a host matrix, such as polymethyl methacrylate or polycarbonate. The process of the invention includes: (a) dissolving the reverse saturable absorber and the host matrix in a suitable solvent to form a solution having a preselected ratio of reverse saturable absorber to host matrix; (b) casting the solution onto a surface to form a film; (c) evaporating the solvent to form a free-standing film; (d) performing steps (a)-(c) for each different desired ratio of reverse saturable absorber to host matrix; (e) stacking the free-standing films in a desired order; and (f) hot-pressing the stack to form the optical limiter having a graded distribution of the reverse saturable absorber in the host matrix. If desired, the stack of films can be placed in a die for hot-pressing. The films can be pre-cut to the shape of the die.

Abstract: Enhanced energy transfers are achieved between optical beams by operating at wavelengths in the near-bandgap region of a photorefractive material, and employing an electrorefractive effect previously proposed only for single beams. An electric field is applied across a photorefractive medium of sufficient intensity to induce an electrorefractive coupling and consequent energy transfer between the beams. Gain enhancements are possible by orienting the photorefractive medium to obtain an electro-optic as well as an electrorefractive effect, and by a moving grating technique. The direction of energy transfer between the beams is controlled by the electric field direction, and can be reversed by reversing the field. Operation in the infrared region is made possible with semi-insulating materials. Applications include optical switches, amplifiers and phase conjugators.

Abstract: A self-pumped phase conjugate mirror and method is disclosed in which an optical beam is applied to a crystal formed from a photorefractive material, the beam is deflected back into the crystal as a return beam to cross-couple with the input probe beam, and an alternating electric field is applied across the crystal to establish a photorefractive index grating shift of about 90.degree. and bring the crystal gain up to a level at which phase conjugation takes place. By a suitable selection of field strength and frequency, and an angle between the probe and return beams within the crystal of less than about 5.degree. (3.degree. for GaAs), semiconductor materials with electro-optic coefficients of less than about 10 picometers/volt can be used as the conjugating medium.