Jian-Hua Dai

Self-focusing and self-trapping in new types of Kerr media with large nonlinearities

Self-focusing and self-trapping of light in common liquid media such as Chinese tea, Chinese herbal medicine, and solutions of chlorophyll have been observed. These materials are found to be new types of natural Kerr media, and their nonlinear coefficients have been determined. Laser-heating-induced self-phase modulation in these materials has also been observed.

Fanning effects in photorefractive crystals.

A model to describe the fanning effect based on the beam-coupling mechanism in photorefractive crystals is presented. The intensity distribution of the fanning beam in a 45 degrees -cut BaTiO(3) crystal is measured experimentally. The results show good quantitative agreement with theory.

Observations of quasiperiodic chaos in plasmas

Abstract We report the experimental observations of Ruelle-Takens and Ruelle-Takens-Newhouse quasiperiodic routes to chaos in a steady-state plasma. The real-time signal, spectrum analysis and Poincare sections are used to confirm these results.

THEORETICAL AND EXPERIMENTAL STUDIES OF FANNING EFFECTS IN PHOTOREFRACTIVE CRYSTALS

A model to describe fanning effects in photorefractive crystals is presented. The intensity distribution of the fanning beam for one incident beam and two incident beams in 45°‐cut BaTiO3 crystals has been studied theoretically and experimentally, with good agreement. The theoretical results suggest that, when there is a fanning effect, only at intermediate effective interaction lengths does the signal beam have a high gain in two‐wave mixing. The transient behavior of the fanning beam in a 45°‐cut BaTiO3 crystal has also been studied theoretically and experimentally.

A two‐dimensional theory and propagation of beam fanning in photorefractive crystals

A general two‐dimensional model to describe beam fanning, which takes into consideration the finite width of the input beam and the interaction between different directions of the fanning beam, is presented. By numerical calculation of the coupled equations, the well‐known curved path of a propagating beam inside photorefractive crystals is explained, and the propagation properties of the fanning beam inside the crystals are studied and discussed.

Laser-heating-induced self-phase modulation, phase transition, and bistability in nematic liquid crystals.

A quantitative discussion of the laser-heating-induced self-phase modulation in nematic liquid crystals is given. The process of the laser-heating-induced nematic-isotropic transition is analyzed. The intrinsic optical bistability due to the nematic-isotropic phase transition is observed and analyzed.

Feedback-induced first-order Freedericksz transition in a nematic film

It is shown that optical-electrical feedback can transform the Freedericksz transition in a nematic film from second order to first order. The criteria that indicate whether the Freedericksz transition is first or second order are obtained. The hysteresis accompanying the first-order transition versus the feedback intensity is discussed. The feedback-induced first-order Freedericksz transition has been observed experimentally. The experimental results are in good agreement with the theoretical analysis.

Frequency locking in optical bistability with competing interactions

We study the unstable behavior of a liquid-crystal hybrid bistable device with two time delays in the feedback mechanism. We report the observation of frustrated instability, frequency locking, and hysteresis on varying the control parameters. The results of our experiments are in agreement with the theoretical analysis presented by Ikeda and Mizuno [Phys. Rev. Lett. 53, (1984)].

Vectorial equations and polarization characteristics of pulsed lasers

Incorporating the vector feature of the laser field, the longitudinal spatial length, and the orientation distribution of the dipole moment in the gain medium, we develop a set of equations that describe the polarization dynamics of a class B laser with a modulated pump, a self-mode-locking laser, and an actively mode-locked laser with a modulated loss. Numerical results show that the first two types of laser operate in a linearly polarized state which changes direction while the third type of laser operates in an elliptical polarization state. In class B lasers with a modulated pump, because the coupling between the light and the medium depends on the dipole moment orientation of the population inversion, and the dominant gain appears alternately in different directions, the changing linear polarization state is induced by the cross-saturation effect of the two orthogonal linearly polarized laser fields. On the other hand, in the self-mode-locking laser the linear polarization state is the result of the coincidence of the dominant field polarization and gain preference for any of the two pulses within the cavity. For the actively mode-locked laser, the gain preference and the dominant polarization of the only pulse in the cavity are always perpendicular to each other, which makes the laser run in an elliptical polarization state.

Frequency shifts and dynamic instabilities in photorefractive self-pumped and mutually pumped phase conjugation

Frequency shifts and dynamic instabilities in photorefractive cat self-pumped phase conjugators and bridge mutually pumped phase conjugators are studied by use of a two-dimensional model. Intrinsic electric fields inside the crystals induce the frequency shifts and dynamic instabilities observed in these experiments. In cat mirrors, for small values of the electric field the phase-conjugate reflectivity and the frequency shift are constant. With a further increase in the electric field the reflectivity and the frequency shift become periodic through Hopf bifurcation. For a large value of the electric field both the reflectivity and the frequency shift fluctuate chaotically. In bridge mirrors, for small values of the electric field the phase-conjugate reflectivity is stable, and no frequency shift exists. With a further increase in the electric field the reflectivity and the frequency shift become periodically oscillating in time. For a large value of the electric field both the reflectivity and the frequency shift fluctuate chaotically. The phase-conjugate outputs of the two beams oscillate in an almost synchronous manner.