Barry J. Feldman

Optical phase conjugation

A process that involves the use of nonlinear optical effects to precisely reverse the direction of p…

High-efficiency pulsed 10.6-Mu m phase-conjugate reflection via degenerate four-wave mixing.

We present the first reported observation in the infrared of nonlinear phase-conjugated reflection. This was achieved via degenerate four-wave mixing in polycrystalline germanium. The observation was facilitated by taking advantage of the counterpropagating (strong) waves internal to a pulsed CO2 laser cavity. The measured effective reflectivity was 2% with a 10-mm interaction length. This simple intracavity technique is generally applicable to any nonlinear material transparent at the wavelength of the laser into which it is inserted.

On-resonant phase-conjugate reflection and amplification at 10.6 μm in inverted CO 2

We have obtained phase-conjugate reflection and amplification with an effective reflectivity exceeding unity by redirecting the output of a TEA CO(2)-laser oscillator into its own gain medium. The intense counterpropagating waves within the laser were coupled through the saturated medium to provide the nonlinearity in a process analogous to degenerate four-wave mixing.

Efficient phase conjugation of an ultraviolet XeF laser beam by stimulated Brillouin scattering.

We report efficient, diffraction-limited, phase conjugation of an XeF (3511-A) laser beam using stimulated Brillouin scattering. Approximately 70% of the 1-GHz bandwidth-locked portion of an injection-locked XeF laser output is phase conjugated by focusing the laser beam at 5 GW/cm (2) into hexane or isopropanol.

Effect of CO2 laser-pulse mode quality on multiple photon absorption in SF6

Abstract Unimolecular multiple-photon absorption cross sections are measured for SF 6 for both single and multiple longitudinal mode CO 2 laser pulses at three different frequencies over a four-decade range of energy fluence. The results indicate only a weak dependence on pulse mode structure for fluence levels corresponding to as little as 0.02 photons absorbed per molecule.

The frequency, fluence, and pressure dependence of the absorption of pulsed CO2-laser radiation by SF6 at 140 K

Abstract We report measurements of absorption of pulsed CO 2 laser radiation by SF 6 at 140 K. These measurements cover a broad range of fluence (10 −6 to 0.8 J/cm 2 ), SF 6 gas density (2 × 10 15 to 6 × 10 16 cm −3 ), and frequency (six CO 2 -laser frequencies within the SF 6 v 3 band). We employ two methods of data reduction including one that gives a simple phenomenological function of the three principal independent variables. We conclude that at low fluence a small fraction of the SF 6 molecules absorb the laser radiation and that collisions and higher fluence both increase that fraction. At higher fluence absorption by vibrationally excited molecules becomes increasingly important.

Transient analysis of nearly degenerate four-wave mixing.

Exact solutions for the impulse responses of the phase-conjugate backward wave and of the transmitted forward wave in a nonlinear four-wave mixing medium with a cw undepleted pump are derived from an earlier analysis of active contraflow systems by Bobroff and Haus [J. Appl. Phys. 38, 390 (1967)].

Ultraviolet phase conjugation

We report the first known demonstration of UV phase conjugation. By use of a 15-psec, 2660-A pulse, 0.1% conjugate reflectivities were obtained through degenerate four-wave mixing in 1-mm samples of CS(2) mixtures. Although pure CS(2) did not exhibit the effect, dilution of CS(2) in several UV-transmitting solvents opened up a concentration- tunable (2450-2850 A) spectral window, allowing the optical Kerr effect to be utilized. Weaker phase conjugation at 2660 A was also observed in other Kerr media and in saturable absorber media.

Multiline short pulse amplification and compression in high gain CO2 laser amplifiers

Abstract Theoretical studies are presented for the amplification and compression of multiline short pulses of CO2 laser radiation at 10.6 μ in a high gain, CO2 laser amplifier. A method of efficiently generating high energy, subnanosecond pulses of CO2 laser radiation is proposed utilizing a pulse tailoring technique recently disclosed by Figueira and Sutphin.

Absorption of pulsed CO(2)-laser radiation by SF(6) at 140 K.

Measurements of absorption of pulsed CO(2) laser radiation by SF(6) at 140 K are reported. Four laser frequencies within the nu(3) absorption band were used, and the laser fluence was varied between 10(-5) and 1.0 J/cm(2). Frequency and fluence trends are discussed, and comparisons are made with room-temperature data. The results indicate that at the SF(6) ground-state band center [P(16), 10-microm line], the fluence-dependent multiple-photon-absorption cross-section curve at 140 K lies slightly above the room-temperature curve, whereas at lower frequencies the low-temperature absorption cross sections are less than 5% of the room-temperature values.