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: An improved phase conjugate master-oscillator power-amplifier laser system for providing a high-power low-distortion laser output beam. The system includes an improved oscillator such as a ring oscillator which rejects any of the output beam which is inadvertently fed back to the oscillator, thereby preventing unwanted oscillation. The system also includes an attenuator such as a spatial filter or an optical isolator that attenuates any amplified spontaneous emissions that may be reflected from the power amplifier to the oscillator, thereby preventing oscillator degradation that would otherwise result. The invention is particularly well-suited for a laser system which employs an SBS mirror for phase conjugation.

Abstract: A self-tuning optical notch filter is employed to separate coherent from noncoherent radiation in an overall beam. The presence of coherent radiation is detected, preferably with an interferometer, and the frequency of the detected coherent radiation is determined. An electrical control signal is generated with a frequency corresponding to that of the coherent radiation, and causes an optical filter to filter out the coherent radiation from the beam. In the preferred embodiment the optical filter is a Bragg cell, and the electrical control signal is applied to an electro-acoustic transducer which furnishes an acoustic control signal to the Bragg cell.

Abstract: A high frequency spectral analysis system and method operates by modulating an optical beam with a high frequency signal to be analyzed, and sampling the beam simultaneously at periodically spaced locations along its length. The sampled portions are then focused to a spectral mapping. In the preferred embodiment a beam is directed in a zigzag pattern through a plate, one surface of which is totally reflective and the opposite surface of which is partially reflective. Periodic parallel samples are obtained from the minor portions of the beam which are transmitted out of the plate through the partially reflective surface. The totally reflective surface is preferably formed as a series of cylindrical surfaces which focus the beam to small spots at the partially reflective surface, thereby permitting a higher spatial density of samples without overlapping. The plate thickness is selected so that the beam is sampled at the Nyquist rate for the highest frequency contained in the signal of interest.

Abstract: A spatial light modulator and associated method are disclosed which achieve an intensity-to-intensity spatial transformation between a noncoherent input beam and a coherent output beam. An intermediate intensity-to-phase modulator provides a coherent, spatially phased modulated readout beam that is combined with a coherent reference beam in an interferometer to yield the desired coherent, spatially intensity modulated output beam. The interferometer also produces a feedback beam with a spatial intensity modulation complementary to that of the input and output beams. The feedback beam is combined with the input beam in a feedback loop that significantly improves the system's response time, and can also enhance the linearity of its transfer characteristic.

Abstract: An electro-optical device (10) is used to alter characteristics of a light beam passing through it. In a particularly preferred embodiment, the device (10) is used as a phase stop having a dynamically variable aperture whose size is defined by the selected application of an electrical potential across one or more concentric, transparent ring-like electrodes (13, 14, 16 and 18). The electro-optical device (10) finds particular utility in a common-path interferometer (40) where fringe visibility is optimized by using suitable servo-electronics (56) to select an appropriate aperture size for the phase stop (10).

Abstract: This invention relates to a laser apparatus having a gain medium disposed along an optical path between a first and second reflector, with the first one being a phase conjugate reflector. The second reflector comprises an SBS medium for generating a moving grating, but without forming an SBS mirror. An output coupling means is positioned between the gain medium and the second, non-phase conjugate, reflector for providing a beam of output radiation. A third reflection means is positioned in the optical path of the laser output beam for intercepting and reflecting a predetermined percentage of the output radiation. This reflected radiation is directed to the back or non-medium side of the second reflector by a fourth reflection means. The fourth reflection means receives radiation from the third reflection means and directs it into the second (SBS) reflector along an optical path toward the laser medium that is substantially parallel to the first optical path of the laser.

Abstract: A laser apparatus (10) has a coherent master oscillator radiation source (30) for driving a plurality of laser gain elements (20) positioned in a operationally parallel configuration so as to receive unamplified radiation (40) from master oscillator (30) and transmitting amplified radiation (44). Input means (60) couples portion of radiation (40) from master oscillator to each of said gain elements (20). Phase conjugate reflector means (80) operatively coupled to gain elements (20) reflects the phase conjugate of amplified radiation (44) back into the gain elements (20) where it is further amplified. Output coupling means (90) couples amplified radiation from the plurality of gain elements (20) out of the laser apparatus as a single coherent output beam of radiation.

Abstract: An acousto-optical isolator for isolating unwanted, backwardly propagating laser beams. The isolator includes a first Bragg cell to shift the frequency of a desired, forwardly propagating beam by a first step, a second Bragg cell to shift the frequency by a second, converse step back to its original value, and an attenuator between the two Bragg cells. The frequency of a backwardly propagating beam is shifted by the second step in the second cell and then is shifted back to its original value in the first cell. The attenuator attenuates a signal having a frequency equal to the original beam frequency shifted by the second step. Accordingly, the backwardly propagating beam is attenuated but the forwardly propagating one is not. Using dual-transducer Bragg cells, the preferred direction of propagation can rapidly be reversed.

Abstract: A phase conjugate resonator (PCR) employing at least one phase conjugate mirror (PCM) provides high resolution spatial detection of individual locations in a two-dimensional optical array which exceed or fall below a threshold level. In one embodiment the optical intensity profile under investigation is imposed either onto one or both of the pump beams of a degenerate four-wave mixing PCM. In another embodiment a pair of PCMs are used as the two mirrors forming the PCR, with the pump beams for one PCM modulated and the pump beams for the other PCM serving as a threshold reference. In either case, the spatially modulated optical output may be read out with multiple detectors or an imaging system, or the cumulative area output of the PCR can be read out with a single detector to characterize the intensity profile relative to the threshold.

Abstract: Apparatus for encoding and decoding laser pulses, or the like. At least one laser source applied laser energy to a nonlinear material in a manner such that counter-propagating beams are applied to the material. These laser beams are spatially or temporally modulated in a predetermined manner. The modulation may be continuous, or discrete, amplitude or phase modulation. Another laser source provides a probe pulse which traverses the nonlinear material and interacts with the counter-propagating laser beams in a manner known as four-wave mixing. This process generates an encoded laser pulse whose modulation pattern is a function of the modulation of the counter-propagating beams. A decoded laser pulse is obtained by applying the encoded pulse to the apparatus and reversing the modulation of the counter-propagating laser beams.

Abstract: A laser using a stimulated Brillouin scattering (SBS) mirror and a moving grating eliminates frequency walkoff of the reflected beams. A laser using a double-SBS mirror prevents frequency walkoff by having the other side of the SBS mirror act as a conjugate moving grating.

Abstract: A Jinc-trap resonator has a Fourier transform resonator structure with a Jinc-trap spatial filter disposed in one of two opposite end transform planes. A near Jinc-like mode is effectively trapped at the one plane where the filter is located, while a corresponding transform mode that is nearly constant in amplitude and flat in phase is located at the opposite transform plane. The Jinc-trap spatial filter is composed of a first series of concentric absorption bands and a second series of concentric reflecting bands which alternate in position with the absorption bands.

Abstract: An imaging detector system for improving the lock-on stability of an optical system and in particular a multi-dither coat system. A quadrant non-coherent detector is disposed beneath a variable stop iris for receiving focused light from a target. The quadrant detector generates a signal in each quadrant sensor region which has a value proportional to the intensity of the light impinging on that sensor region. The signals so generated are processed in a signal processor to generate x-y steering command signals which drive a motor which in turn drives a slewing mirror so that the area of the quadrant detector upon which the greatest light intensity occurs is centered relative to the iris aperture when viewed in the direction of the return optical energy. When the high-intensity region is centered, the aperture of the variable stop iris is decreased to prevent the problem of glint jump.

Abstract: Dual-wavelength coherent optical adaptive systems which comprises means for adaptively forming a first beam of a first wavelength, on a target and for deriving therefrom information defining characteristics of phase perturbations in the propagation path to the target; and means responsive to said information for compensating for propagation path distortions for a second beam of a second wavelength which is simultaneously transmitted along a substantially identical path to that of said first beam.

Abstract: A polarization reference imaging system to determine image of a target comprises three basic major elements. Such elements consist of transmitting means, a matrix of receiving systems and digital processing circuitry. The transmitting means consists of a transmitter and suitable optics for electromagnetically illuminating a target. The receiving systems consist of a matrix of receivers electromagnetically coupled to the target for receiving energy as reflected signals due to illumination of the target which signals are passed by the receiver substantially devoid of atmospheric distortion components. Each of the receivers of the receiving system provide a different weighting factor insofar as amplitude of the received signals is concerned, thereby enabling to obtain not only the shape of the target but also the various intensities of grays, blacks and white of the illuminated target. The digital system is connected for processing the received signals.

Abstract: Disclosed herein is an imaging system comprising a linear array of receivers and a single transmitter deployed and operated in such a manner as to produce the equivalent of a completely filled, two-dimensional array.

Abstract: An adaptive energy telescope having a linear sensor for detecting a received optical image. A movable mirror phase shifter is positioned near the telescope aperture and is responsive to the received optical image. A linear image quality sensor is optically coupled to the phase shifter. The phase shifter may have a plurality of mirrors each attached to a piezoelectric crystal so that the mirrors are displaced in accordance with the voltages impressed across the piezoelectric crystals. This phase shifter may also be provided with a single planar reflective sheet instead of a plurality of mirrors. The sensor may consist of a plate with a pinhole for admitting a portion of the optical image and a transducer at one side of the plate for converting the portion to an electrical signal. The sensor may also consist of a transform of the Fourier or Hadamard types and a low and high frequency detector optically coupled to the transform mechanism which in turn is electrically connected to an electronic divider.

Abstract: An optical target imaging system having a laser transmitter that provides a dual pulse sequence target illuminating field. One pulse of the dual pulse field is predominantly polarized in one direction and the other pulse is predominantly orthogonally polarized. At least two receivers for receiving the energy reflected from target in a predetermined polarization state processes the target information. Ultimately, the receiver outputs providing sample signals in Fourier or like transform format are fed to a digital computer that inverse transforms such signals to generate an image. A visual display of the target or data comprising display information is made possible by feeding the computer output into a CRT system or a data recording terminal.

Abstract: An adaptive imaging telescope having nonlinear sensing means for detecting an optical beam received thereby. The system comprises a phase shifter, positioned at the aperture of the telescope, responsive to the optical beam. This system also includes a nonlinear image quality sensor, optically coupled to the phase shifter, comprisinng a photodetector plate responsive to the optical beam for converting the optical beam into an electrical signal. Analog circuits are provided to receive the sensor output and provide a closed-loop return to the phase shifter.