United States of America As Represented by the Secretary of the Air Force

David A Cardimona

Phillip R Peterson

Athanasios Gavrielides

Mohinder P Sharma

System and method for selectively inducing transparency to laser radiation in a material are described comprising a material having a ground state and two closely-spaced first and second excited states wherein the transition dipole moment d.sub.1 between the ground and first excited states is parallel to the dipole moment d.sub.2 between the ground and second excited states, and wherein d.sub.1 is substantially equal to zd.sub.2 where z is a scalar constant characteristic of the material, and wherein the frequencies of transition between the ground and first excited states and between the ground and second excited states are .omega..sub.o and .omega..sub.o +.DELTA., respectively, and a source of laser radiation for substantially totally irradiating the material with laser radiation of frequency .omega..sub.L substantially equal to .omega..sub.o +.DELTA./(1+z.sup.2).

Method and apparatus for field-induced transparency using laser radiation

Multibeam coupling in a Kerr medium of nonlinear characteristics and finite response time is disclosed together with two different frequency spectrum examples of its use. In the first spectrum example, the modes are equally spaced and in the second spectrum the frequency separations are all unequal. In either case, as the beams propagate, both input spectra eventually reach a saturation characterized by a cascading of energy into the lowest frequency if the Kerr constant is positive. The direction of cascading of energy transfer is reversed to the highest frequency if the Kerr constant is negative. The examples disclosed include a typical Kerr medium and are representative of a multimode, equally spaced laser source and an unequally spaced source. For the equally spaced case, the optimum medium response time for conversion of Gaussian spectra is disclosed. If the frequencies are unequally spaced general conditions to be satisfied are disclosed, along with examples.

Laser line narrowing and frequency shifting

An optical parametric amplifier system is used to illuminate an object of interest with a signal beam, and parametrically mix the signal beam from the object with a pump beam to produce a down converted idler beam which maintains an image of the object of interest but which has a frequency which equals the difference between the frequencies of the pump beam and the signal beam. A signal laser is used to illuminate the object of interest, while a pump laser produces the pump beam. A beam combiner mirror produces a combined output by receiving and combining the pump beam and the signal beam. Finally, a nonlinear crystal receives and down converts the combined output of the beam combiner mirror to produce the idler beam by parametrically mixing the signal beam with the pump beam. When a KDP nonlinear crystal is used, the crystal optic axis may be rotated with respect to the direction of propagation of the idler beam to spectally score and amplify the image of the object of interest.

Optical parametric amplifying variable spatial filter

Normal stimulated Raman scattering (SRS) is done in a gas cell with pump and Stokes seed input beams. The pump photons excite gas molecules in the gas cell from their ground state and the Stokes seed photons stimulate the de-excitation of the molecules back to a lower state (emitting more Stokes photons in the process). The SRS enhancer entails inputting another beam at a frequency, different from the pump and seed, tuned between a third molecular state and the Raman virtual state created by the pump/seed off-resonant two-photon transition. The third laser enhances the Raman virtual state, thereby also enhancing the two-photon transition rate. Since the two-photon transition is the SRS process, the Stokes amplification is enhanced.

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Albuquerque, NM, United States of America

David A Cardimona