Abstract: The present invention relates to an improved process for photorefractive index grating formation utilizing polymeric photorefractive materials. The process involves the steps of: (i) exposing a polymeric optical article to electromagnetic radiation having an intensity of at least 0.05 W/cm2 for a short period of time to achieve an absorbed energy/unit volume of at least 1×103 J/cm3 to activate the article, and (ii) exposing the polymeric optical article to an electric field and electromagnetic radiation to form an index grating.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.