R. C. Lind

Degenerate four-wave mixing in absorbing media

Degenerate four-wave mixing in a two-level absorbing (or amplifying) system is treated, leading to a quantitative description of amplified reflection, oscillation, and phase conjugation.

Demonstration of image transmission through fibers by optical phase conjugation.

We have demonstrated image transmission through a multimode fiber by using optical phase conjugation. By using the wave-front reversal properties of degenerate four-wave mixing, we have compensated for the degradation of the image that is due to modal dispersion in a fiber.

Demonstration of the longitudinal modes and aberration-correction properties of a continuous-wave dye laser with a phase-conjugate mirror

We have experimentally demonstrated a cw dye laser incorporating a phase-conjugate mirror (PCM). The mirror was generated by using four-wave mixing in sodium. The unique bandwidth and pump–probe detuning properties of such a PCM permitted the first reported demonstration of the c/4L spaced paired half-axial modes. In addition, the aberration correction ability is demonstrated.

Imaging threshold detector using a phase-conjugate resonator in BaTiO 3

We have demonstrated an imaging threshold detector using a phase-conjugate resonator to provide high spatial resolution and signal regeneration near threshold. The device is based on spatially resolved grating erasure in photorefractive BaTiO(3) and has the capability of high resolution and low cross talk.

Polarization‐rotation and thermal‐motion studies via resonant degenerate four‐wave mixing

We report experimental observation of polarization rotation in resonant degenerate four‐wave mixing (DFWM) arising from the third‐order coupling of the electric fields. This effect allows investigation of molecular motion and its effect on the efficiency of the DFWM. By controlling the pulse width and therefore γ=T0/τp (where T0≡λ/vth) we show quantitative agreement with a third‐order density matrix perturbation calculation. In particular, using a CO2 laser at 10.6 μm and SF6 as the nonlinear medium, we show that for γ≫1 (stationary limit) we see no molecular motion and for γ≈1, we see a significant ’’washout’’ of one third–order polarization.

Phase conjugation at 10.6 μm by resonantly enhanced degenerate four‐wave mixing

A resonantly enhanced phase‐conjugate 10.6‐μm signal has been generated in the saturable absorber SF6. Direct evidence of aberration correction is shown through the use of far‐field photographs taken with a pyroelectric vidicon camera. Reflection coefficients of 7% have been achieved in a few Torr of SF6 for a 2‐cm interaction length.

High-efficiency degenerate four-wave mixing of 1.06-μm radiation in silicon

We report detailed experimental results on degenerate four-wave mixing of 1.06-μm laser radiation in silicon. Using ~100-mJ pump pulses of 15-nsec duration from a Q-switched Nd:YAG laser at intensities of ~6.8 MW/cm2, we obtained an energy conversion of over 150% for the probe-to-signal reflection.

Multiresonant behavior in nearly degenerate four-wave mixing: the ac Stark effect

We have experimentally studied the effects of pump-probe detuning in nearly degenerate four-wave mixing. The data show multiresonant behavior as a function of the pump-probe detuning at both low and high intensities. At low intensities, the structure is the result of Doppler motion. At high intensities, five-peak structure is observed and is explained by the standing-wave modulation of the ac Stark splitting of the atomic levels.

Phase Conjugation By Resonantly Enhanced Degenerate Four-Wave Mixing

The use of resonantly enhanced four-wave mixing to generate high reflectivity phase-conjugate waves is discussed. A physical understanding of the mechanisms underlying the nonlinear response for a simple two-level system is presented followed by a discussion of the complicating effects of pump absorption, pump depletion, unbalanced pumps, and thermal motion. Modifications of the theory to describe four-level behavior are presented and compared with experiments. The application of nearly degenerate four-wave mixing to narrow-band filtering complicated by the A. C. Stark effect is dis-cussed along with examples of experimental observations.

Phase conjugate master oscillator‐power amplifier using BaTiO3 and AlGaAs semiconductor diode lasers

A double pass phase conjugate master oscillator‐power amplifier has been demonstrated at 820 nm using AlGaAs gain elements and BaTiO3 in a self‐pumped ring configuration. Single frequency operation with diffraction‐limited output beam quality was achieved at output powers in excess of 50 mW cw.