Robert A. Fisher

Optical phase conjugation

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

SUBPICOSECOND PULSE GENERATION USING THE OPTICAL KERR EFFECT

A frequency modulation which is monotonic in time over a portion of an optical pulse can be utilized together with a dispersive delay line to obtain temporal compression of the pulse envelope. Short pulses (picosecond range) passed through an optical Kerr liquid receive a self‐phase‐modulation which exhibits a frequency sweep in the region of maximum intensity, the slope in time being proportional to the propagation distance. Frequency spreads of the order of 103 cm−1 are obtainable and hence significant compression ratios should be possible, giving rise to very short pulses in the range of 10−14 to 10−13 sec.

Numerical studies of the interplay between self-phase modulation and dispersion for intense plane-wave laser pulses

A computer algorithm is presented which allows simultaneous consideration of self‐phase modulation and dispersion for predicting temporal shape changes during the propagation of plane‐wave intense light pulses. The algorithm entails considering propagation alternately in regions where only one of the two above effects is operative. It is shown for clear materials that the parameters characterizing propagation are the nonlinear index change, the wavelength λ, the relaxation time of the nonlinearity, and the disperison parameter λ3(d2n/dλ2). The thickness of material over which a pulse will significantly reshape is found to be √λ times the geometric length of the pulse divided by the square root of the product of the dispersion parameter and the maximum nonlinear index. It is demonstrated that dispersion significantly modifies the self‐steepening concept of DeMartini, Townes, Gustafson, and Kelley. Numerical simulations of propagation in CS2 indicate that, after sufficient travel, a shock can form on the le...

Optical phase conjugation for time-domain undoing of dispersive self-phase-modulation effects

We show that the temporal distortion and spectral broadening of a pulse generated by the combined effects of group-velocity dispersion and self-phase modulation is removed by reflection of a cw-pumped, broadband, unityreflecting Kerr-like optical phase conjugator followed by retraversal of the nonlinear medium. We also examinenumerically the effects of finite linear loss in the material, of nonunity conjugate reflectivity, and of finite conjugator thickness.

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.

Phase locking two beams by means of seeded Brillouin scattering

We have demonstrated that the phases of the stimulated Brillouin scattering reflections of two separately focused pump beams can be locked to a common phase by a backward seed of pump laser light.

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.

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.

Pulse compression for more efficient operation of solid‐state laser amplifier chains

We propose a pulse compression scheme which reduces the peak intensity while increasing the energy density achievable in a Nd:glass amplifier chain. Self‐focusing is the dominant effect responsible for limiting the power of a short‐pulse Nd:glass amplifier chain, and the reduction of the intensity (through this compression scheme) greatly reduces these problems. We recommend injecting a lower‐intensity and longer‐duration pulse into the chain. Under some circumstances, the glass nonlinearity will impress upon the pulse a chirp suitable for efficient subsequent temporal compression, and this may result in higher effective peak power operation. If a 1‐nsec (full 1/e duration) temporally Gaussian pulse with a chain‐averaged peak intensity of 2 GW/cm2 propagates 2 m in a Nd:glass laser chain, we calculate that the pulse could be subsequently compressed (by a series of Gires‐Tournois interferometers) to 125 psec with good stability against input pulse amplitude noise. Such short pulses are of major interest fo...