Abstract: A Fresnel lens is fabricated by depositing concentric layers of first and second materials in alternation on a substrate surface. The substrate and deposited layers are then drawn down to provide a predetermined Fresnel lens zone structure.

Abstract: A Fresnel lens is fabricated by depositing concentric layers of first and second materials in alternation on a substrate surface. The substrate and deposited layers are then drawn down to provide a predetermined Fresnel lens zone structure.

Abstract: A photodetector, and a method for detecting electromagnetic radiation, is disclosed. The photodetector includes a body which undergoes a detectable, internal physical or chemical change when exposed to electromagnetic radiation, as well as means for detecting this change. The photodetector also includes a substantially periodic surface which increases the efficiency with which incident electromagnetic radiation is coupled onto the photodetector.

Abstract: A photodetector, and a method for detecting electromagnetic radiation, is disclosed. The photodetector includes a body which undergoes a detectable, internal physical or chemical change when exposed to electromagnetic radiation, as well as means for detecting this change. The photodetector also includes a substantially periodic surface which increases the efficiency with which incident electromagnetic radiation is coupled onto the photodetector.

Abstract: Metal ellipsoidal particles are deposited on an ordered array of silicon dioxide posts. Each of the particles has dimensions that are less than the wavelength of a fundamental beam to be used in the generation of second harmonic radiation. The rows of particles in the ordered array are spaced at a distance that is less than one-half of the fundamental wavelength and greater than one-half of the second harmonic wavelength.

Abstract: An apparatus utilizing four-wave degenerate mixing detects birefringence in irregularly shaped objects (6). Laser radiation (120) having a specified polarization is brought to a focus and then sent through the irregularly shaped object. The emerging radiation impinges upon a nonlinear material (8) to form a conjugate beam by means of four-wave degenerate mixing. The conjugate beam, which passes back through the object, is picked off and detected at a replica of the focus point. The detector (10, 11 and 12) includes a polarization detector (10) which is arranged so that a signal is detected only when the object has birefringence.

Abstract: Saturation spectroscopy involving synchronous phase-sensitive detection and measurement of the intensity of the output when one of the input beams is chopped has a drawback that scattered light and fluorescence from the sample will also be chopped and produce a large background signal. According to the present invention, the direction of propagation of one of the input beams is modulated. This causes the direction of propagation of the output to be similarly modulated while producing only a negligible effect on the background radiation from scattering and fluorescence.

Abstract: Linear phase aberrations in laser amplifier systems are adaptively corrected by a device which propagates an object beam formed by reflection of a laser beam from a target backwards through a laser amplifier chain in order to sample the linear phase aberrations and produces a conjugate image beam by degenerate four-wave mixing in a medium having a third order nonlinearity in susceptibility. The conjugate image beam which is amplified as it propagates back through the laser amplifier chain has the linear phase aberrations removed. The device also corrects for birefringent aberrations contained in the laser amplifier chain when (1) the medium has an isotropic nonlinearity; (2) the polarization of the pump beams, required for four-wave mixing, lies in the plane formed by the object beam and the pump beams; and (3) the angle between the object beams and the pump beams is substantially 90 degrees. The degenerate four-wave mixing is accomplished in one embodiment by gain saturation in Nd:YAG.

Abstract: A wide angular aperture, tunable filter device is achieved by using degenerate four-wave mixing. The apparatus utilizes two counter-propagating pump beams at substantially the same frequency to interact with an object beam, containing a spread of frequency components through a third order nonlinearity in the susceptibility of a medium. This produces a conjugate image beam formed with frequency components close to the frequency of the pump beams. By tuning the frequency of the pump beams the object beam frequency spectrum may be scanned while preserving all of the spatial information in the object beam. Apparatus for generating velocity contours of moving objects is also disclosed.

Abstract: A high speed, wide angular aperture, spectrally selective optical gate is achieved by using degenerate four-wave mixing. The apparatus utilizes two counterpropagating pump beams to interact with a probe beam through a third order nonlinearity in the susceptibility of a medium to produce an image beam which is counterdirectional to the probe beam. The image beam is produced only during the time that the two pump beams and the probe beam are coincident in time and space in media having a fast nonlinearity. In slow media, fast gating is achieved by turning off both pump beams after the probe beam and the pump beams have interacted. This apparatus produces gate times which are not limited by the speed of relaxation of the nonlinearity in the medium utilized.

Abstract: The invention relates to an ellipsometer for measuring the degree of elliptical polarization of a beam of coherent optical radiation. Applications of the invention include a device for measuring birefringence and a material detector for measuring small concentrations of substances in a gaseous medium.