T. H. Liu

Passive optical self-limiter using laser-induced axially asymmetric and symmetric transverse self-phase modulations in nematic liquid crystals

Using low-power cw lasers in conjunction with the symmetric and asymmetric nonlinear transverse self-phase modulation imparted by a nematic liquid-crystal film, we have demonstrated two forms of transverse intensity-switching and power-limiting operations. Applications to high-power nanosecond laser are also feasible.

Low-power (10.6-μm) laser-beam amplification by thermal-grating-mediated degenerate four-wave mixing in a nematic liquid-crystal film

We present a detailed theoretical analysis of degenerate four-wave mixing by a laser-induced thermal grating in a nematic liquid-crystal film. In particular, we show that the coupling of the (strong) pump beam to the first-order diffracted beam can give rise to substantial amplification of a (weak) probe beam. Experimental verification of this effect with a CO2 laser beam is also made. A probe-beam gain of greater than 20 can easily be observed in a 120-μm film with a pump intensity of the order of a few watts per square centimeter.

Probe beam amplification via two- and four-wave mixings in a nematic liquid crystal film

We have observed very large probe beam gain (up to 600 percent) in a thin film (100 μm) of nematic liquid crystal for a low pump beam intensity on the order of 2 W/cm2. The effect is nonlinearly dependent on the pump intensity and the wave mixing angle.

Laser Spot Size Dependence, Nonlocality And Saturation Effects In Transverse Optical Bistability

We present here a theoretical discussion of the effect of nonlocality and saturation in transverse optical bistability. It is found that the switching conditions, switching power and characteristics are considerably different from the situation where these effects are not accounted for. We also include an analytical study of the transverse self-phase modulation effect and relate the key parameters explicitly to the transverse bistability switching condition and bistability.

1.06 μm nanosecond laser amplification via degenerate multiwave mixings in silicon

Degenerate multiwave mixing and optical phase conjugation in semiconductor silicon are reexamined both theoretically and experimentally. It is found that, in general, the often neglected diffracted beams influence considerably both the forward as well as the backward phase conjugated signal gain.

Infrared Optical Wave Mixing And Beam Amplification With Liquid Crystal Nonlinearity

We present a detailed theory and experimental study of infrared optical wave mixing based on thermal nonlinearity in nematic liquid crystal films. Because of the longer wavelength of infrared laser, lower scattering loss, transparency and other unique physical characteristics, very efficient degenerate optical wave mixing effects can be realized in nematic liquid crystal films. Applications to fairly fast (submillisecond) phase conjugations, beam and image amplification and self-pumped phase conjugation are also discussed.

Four Wave Mixing With Gain Using Liquid Crystal Films

The extraordinarily large thermal and orientational nonlinearities of nematic liquid crystal is studied in the context of amplified reflection in four wave mixing. Greater than 100% reflection in wavefront conjugation can be obtained.

Optical Limiting Using Self-Focusing And Self-Bending Of Light By A Nematic Liquid Crystal Film

Optimal power limiting effects associated with self-focusing and self-bending of light in nematic liquid crystal films are studied using low power cw lasers and high power nanosecond pulse lasers.