Liu Jin-song

Screening-photovoltaic spatial solitons in biased photovoltaic–photorefractive crystals and their self-deflection

Steady-state dark (or bright) spatial solitons are predicted for biased photovoltaic–photorefractive materials when the diffraction of an optical beam is exactly compensated for by nonlinear self-defocusing (or self-focusing) that is due both to the photovoltaic effect and to spatially nonuniform screening of the applied field. These solitons differ from previously observed steady-state photorefractive or photovoltaic spatial solitons in their properties and experimental condition. These biased photovoltaic solitons are known as the screening-photovoltaic solitons. If the bias field is much stronger than the photovoltaic field, then the screening-photovoltaic solitons are just like the screening solitons. If the applied field is absent, they degenerate into photovoltaic solitons in the closed-circuit condition. We investigate the self-deflection process of bright screening-photovoltaic solitons by taking diffusion effects into account. By use of perturbation techniques it is found that the center of the optical beam moves on a parabolic trajectory and, moreover, that the central spatial-frequency component shifts linearly with the propagation distance. Both the spatial deflection and the angular deviation are proportional to the sum of two dimensionless quantities that are associated with the bias field and the photovoltaic field, respectively. The drift process and the photovoltaic process play an equivalent role in the self-bending process.

Anomalies of Doped-LiNbO3 Crystal in Photorefractive Phase Conjugation with Relation to Structural Phase Transformation

We investigate the photorefractive phase conjugation in a Ce:Fe:LiNbO3 crystal as a function of temperature (293-393 K) and find the phase conjugate reflectivity increases sharply in the vicinity of 55, 70 and 110° C. The anomalous phenomenon is possibly concerned with the structural phase transformation of a crystal, which induces an extra internal electric field to influence the phase conjugation. The value of the field is estimated at the order of 105 V/m, in agreement with the published data.

Measurement of Three Parameters of a Photorefractive Crystal Ce:KNSBN in Codirectional Two-Wave Mixing

We present a method of measuring the parameters of a photorefractive crystal in codirectional two-wave mixing that is suitable for two-wave mixing in the intermediate stage (before saturation). Three parameters of a crystal, the exponential gain coefficient, saturation intensity and intensity absorption coefficient, can be measured simultaneously by using this method. The three parameters of a Ce:KNSBN are measured and the measured data are checked by another independent measurement.