Bell Telephone Laboratories

Gary Carl Bjorklund

Paul Foo-Hung Liao

David M Bloom

Linn F Mollenauer

Paul F Liao

Walter J Tomlinson, Iii

John E Bjorkholm

Richard R Freeman

Ralph H Storz

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.

Tunable wide angular aperture filter by degenerate four-wave mixing

An apparatus is disclosed for servo-locking the angular orientation of a nonlinear crystal to the angle at which phasematching occurs for nonlinear optical frequency mixing processes. Two secondary beams are generated from a beam of radiation which is incident upon the crystal. They travel through the crystal at small angles with respect to the main beam and each generates a secondary output beam containing new frequency components produced by the nonlinear optical frequency mixing process in the crystal. A discrimination signal is created by subtracting the generated power at the new frequency component of one of the secondary output beams from the generated power of the other. This signal is sensitive to the angular misalignment of the crystal and is used to drive a servo system to maintain the proper angular orientation for phasematching.

Servo-control alignment of nonlinear crystals

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.

Sub-picosecond optical gating by degenerate four-wave mixing

A switchable diffraction grating may be formed from an array of color centers in an alkali halide crystal. These gratings will diffract only when the color centers are excited by an external light source, so that they may be switched on and off. The gratings may be used to form optical switches, pulse shaping devices, and Q-switched lasers.

Switched diffraction grating

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.

Self-induced rotation ellipsometer

Apparatus for piecewise generation of grating-like patterns in photoresponsive material with a coherent the class which splits the coherent beam into two component beams. The two component beams intersect forming a parallel plane interference pattern on a section of the photoresponsive material. An arrangement which translates the beam parallel to itself forms the interference pattern in registration with the previously generated pattern on a different section of the photoresponsive material.

Apparatus for piecewise generation of grating-like patterns

A source of tunable vacuum ionizing radiation is disclosed in which the range of resonance enhancement is extended by Stark-shifting the frequencies of autoionizing states in the continuum of the conversion medium.

Stark tuning of four-wave mixing processes

A method and apparatus for phase-matching the output of a four-wave nonlinear optical mixing process is disclosed. The method produces phase-matching that is independent of variations in density of the conversion medium and extends over the entire frequency spectrum from the far infrared to the vacuum ultraviolet. The phase-matching is accomplished by adjustment of the frequencies of three input lasers so that the desired frequency is produced, the condition for two-photon resonance enhancement is met, and the phase-matching condition is satisfied.

Method and apparatus for phase matching by adjustment of the fundamental

An optical polarization rotator is implemented without any magnetic field by using dispersion due to two-photon transitions. The polarization rotator is useful for powerful coherent linearly-polarized optical beams. A second powerful circularly-polarized coherent optical beam provides control for the polarization rotation of the linearly-polarized beam which interacts more strongly with the oppositely circularly-polarized component of the first beam than with the other component of the first beam. The difference in interaction occurs because the gaseous medium atoms in the cell in which the interaction occurs begin and end a nearby resonance transition that determines the two-photon dispersion in the same angular momentum state; and, because of this quantum state selection rule, the result is a relative delay between the two circularly-polarized components of the linearly-polarized beam and a consequent rotation of the orientation of linear polarization.

Polarization rotator based on dispersion due to two-photon transitions

Two different pulse compressors for relatively intense optical beams differ from the prior art both in employing a two-photon dispersion effect and in employing a different set of modulations than is conventional for 'chirped' pulse compressors. The first one depends upon turning on and then turning off a two-photon dispersion effect of an atomic gaseous medium upon a first coherent beam from which the pulse is to be formed. The effect is turned on and off by the second beam within a time period not substantially more than the length of the medium divided by the dispersive group velocity of the first beam in the medium. The dispersion in effect allows energy to be concentrated in the medium by means of a temporary delay. The second device is analogous to that of U.S. Pat. No. 3,679,313 to R. L. Rosenberg, issued July 25, 1972, in employing overlapping 'comb' patterns of modulation products but differs therefrom in that it replaces the dispersive interferometer with the two-photon dispersive gas medium and employs much wider frequency modulations. The first beam is chirped, or frequency-modulated, at a first rate; but the second beam is frequency-modulated at a rate sufficiently different from that of the first beam that the modulation product combs intermesh to provide two-photon interaction over the broadest possible frequency band.

Optical pulse compressors employing modulations affecting the two-photon

The disclosed distributed feedback laser employs an alkali halide crystal having a spatially modulated pattern of a stable color center and a complementary spatially modulated pattern of U-centers. The stability of the color centers is provided by initial additive coloration, conversion to U-centers, and subsequent reconversion; and the spatial modulation is provided by patterning the reconversion by exposing a portion of the crystal to an interference pattern of coherent light. Conversion occurs by two-photon absorption. The very large penetration depth and the use of ultraviolet frequencies that are only about one-half of the magnitude of the frequencies that would otherwise be required make this device and process attractive for thick holograms and for distributed feedback devices such as lasers.

Growing community of inventors

West Windsor, NJ, United States of America

Gary Carl Bjorklund