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Transformation circle theory is simpler than other methods for analyzing laser resonators. In our analysis only a circles and simple mathematical knowledge are used to analyze the stability and calculate the parameters of the laser resonator, which further simplifies the transformation theory. The results agree well with the well-known matrix theory. Two- and three-mirror (including a thermal lens) laser resonators are used as examples to present the stability formula and the Gaussian beam dimensions at the mirrors. Furthermore, we apply the commonly used example in which the laser medium is close to the cavity mirror. OCIS codes: 080.2720, 140.3410, 140.4780.

The influence of composition on the photorefractive effect in pure LiNbO3 crystals at low light intensity was investigated. The experimental results indicate that different defects dominate the photorefractive centers of pure LiNb[O.sub.3] with various compositions. Bipolarons are considered to be responsible for the enhanced photovoltaic field in reduced near-stoichiometric LiNbO3, and their bulk photovoltaic constant K is estimated to be ~6.95 x [10.sup.-32] [m.sub.3]/V. Q polarons (composed of two bipolarons) are introduced to explain the photorefractive effect of congruent LiNb[O.sub.3] at both low and high light intensities.

A method of measuring the refractive indices of minute samples by analyzing capillary interferometry is introduced. With the interference theory of light, the intensity distribution of an interference fringe pattern formed by a cylindrical tube of a capillary is obtained, and the influence of some parameters on the fringes are discussed. The measurement accuracy and its relative problems are analyzed. OCIS codes: 120.3180, 120.5710, 260.3160.

The threshold effect of incident light intensity in doped LiNbO3 crystals was experimentally studied.

A study was conducted to investigate the origins of the threshold effect of the incident light intensity associated with the photorefractive light-induced scattering in LiNbO3:Fe,M crystals. Variations in the photovoltaic field were computed based on the conductivity and ratio of the incident light intensity. Results indicated that that the increased dark conductivity of the crystal is the origin of the threshold effect of incident light intensity.

We demonstrate that (1+1)-dimensional and (2 + 1)-dimensional waveguides can be induced by self-focused dark notches and crosses and stored in LiNb[O.sub.3]:Fe crystals. This is very valuable for information processing and integrated optics. The self-focused dark notches and crosses may be related to the formation of (1 + 1)-dimensional and (2 + 1)-dimensional photovoltaic dark spatial solitons in LiNb[O.sub.3]:Fe crystals. Key words: Photorefractive, self-focused, waveguides.

We show a double phase conjugator with novel crystals of copper-doped potassium sodium strontium barium niobate. The phase conjugation reflectivity can reach 278% and depends on relative input positions of both incident beams. The response time with the input beam power ratio is measured and modeled as a function of input beam power ratio. The formation of the arch coupling loop is analyzed with theoretical simulation results and a positive feedback process is proposed. The influence of a self-pumped phase conjugation process on double phase conjugation fidelity is also discussed. It is necessary to avoid generating self-pumped phase conjugation to prevent the reduction of double phase conjugation fidelity.

On the basis of the idea that signal gratings have a faster formation rate than noise gratings and signal gratings have a slower erasure rate than noise gratings under the same erasing beam, we report a new technique to suppress or eliminate the noise in image processing in photorefractive crystals. A general theoretical analysis and experimental results in LiNb[O.sub.3]:Fe crystals are given. Key words: Photorefractive, noise suppression, time constant.

We theoretically and experimentally study phase contrast using a photorefractive LiNb[O.sub.3]:Fe crystal sheet and realize the high-performance phase contrast operation using C-cut LiNb[O.sub.3]:Fe crystal sheets in which the photovoltaic effect plays an important role. We estimate the maximum photovoltaic field in LiNb[O.sub.3]:Fe using the phase contrast method.

We present a theoretical analysis of beam propagation in thick nonlinear media by using the Gaussian decomposition method and considering a thick medium as a stack of thin media. Simple analytic solutions of Z-scan characteristics and optical limiting with thick nonlinear media are obtained. Comparisons of these results with those obtained by use of a distributed-lens model and Gaussian-Laguerre mode decomposition are made. Good agreement is obtained with a distributed-lens model.

The storage application of the light-climbing effect in a LiNb[O.sub.3]:Fe crystal has been studied experimentally. A new type of photorefractive storage in LiNb[O.sub.3]:Fe crystals, in which one could write the multipage simultaneously and at a later time read out the multistored pages, using only one readout beam simultaneously, has been demonstrated successfully. Furthermore the signal-to-noise ratio of the output images was high because the climbing lights suppressed the fanning noise scattering lights. Key words: Light climbing, photorefractive storage, multipage storage.

The light-climbing effect in a LiNbO3:Fe crystal sheet was experimentally studied, and the mechanism for light climbing proposed was proved to be correct. The relevant optical properties were investigated.

Using the Czochralski method and vapor transport equilibrium technique, magnesium oxide doped stoichiometric LiNbO3 crystal was produced. The results state that MgO:SLN crystal is an attractive material for fabricating the periodically domain inversion structures.

We investigated the temporal evolution of light-induced scattering in [LiNbO.sub.3]:Fe,In crystals with different doping concentrations. A special behavior of the beam fanning was found when the intensity of the incident light was relatively weak. In this case the beam fanning became stronger at the beginning of the illumination and then was greatly reduced, which was observed only at strong incident light intensities. This phenomenon was analyzed on the basis of the saturation space-charge field. The intensity threshold effect and the concentration threshold effect were successfully explained. OCIS codes: 160.5320, 090.2900.

A method to determine the focal length of a thermal lens and pumping laser beam waist in the gain medium in laser-diode-pumped solid-state lasers is presented. This method, using resonator transform circle theory, is both simple and reliable. The measured focal length of the thermal lens is used to calculate the beam waist of pumping laser inside the gain medium. The effect of the thermal lens on the output power is also measured and analyzed. [ABSTRACT FROM AUTHOR]