Bell Telephone Laboratories

Paul Foo-Hung Liao

Gary Carl Bjorklund

John E Bjorkholm

Heinz Paul Weber

Bruce Cedric Tofield

Paul Michael Bridenbaugh

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

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

Improved atomic beam deflection and improved isotope separation, even in vapors, is proposed by substituting the A.C. Stark effect for the baseband chirp of the pushing beam in the prior proposal by I. Nebenzahl et al, Applied Physics Letters, Vol. 25, page 327 (September 1974). The efficiency inherent in re-using the photons as in the Nebenzahl et al proposal is retained; but the external frequency chirpers are avoided. The entire process is performed by two pulses of monochromatic coherent light, thereby avoiding the complication of amplifying frequency-modulated light pulses. The A.C. Stark effect is provided by the second beam of coherent monochromatic light, which is sufficiently intense to chirp the energy levels of the atoms or isotopes of the atomic beam or vapor. Although, in general, the A.C. Stark effect will alter the isotope shift somewhat, it is not eliminated. In fact, the appropriate choice of frequencies of the pushing and chirping beams may even relax the requirements with respect to the isotope absorption line shift for effective separation. That is, it may make the isotope absorption lines more easily resolvable.

Deflection of atomic beams with isotope separation by optical resonance

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

Acicula of rare earth pentaphosphates, of a diameter and length ideal for waveguiding laser-type applications, are grown by controlling the rate of metaphosphoric acid conversion by introducing water vapor into an inert gas atmosphere continuously flowed through the reaction zone. The required amount of water vapor in the reaction zone has to be within the range between approximately 14 grams per cubic meter and 290 grams per cubic meter of the flowing atmosphere. This control is implemented by bubbling the inert gas atmosphere through a water bath at temperatures between 15.degree. and 80.degree. C. It is believed that the control of the water vapor eliminates problems of supersaturation in the forming of pentaphosphoric crystals in the growth solution and thereby promotes their natural tendency to form purely chainlike polymer structures.

Process for growing acicula of rare earth pentaphosphates

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.

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Middletown, NJ, United States of America

Paul Foo-Hung Liao