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Transformation circle theory is simpler than other methods for analyzing laser resonators. In our analysis only sigma 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.

UV-light-induced absorption in LiNbO(3) highly doped with Mg and Hf was investigated. Distinct decay behavior was attributed to the different centers formed under UV illumination, i.e., the shallow and intermediate deep centers for trapping holes. O- formed near doped cation at the niobium site was suggested to be the origin of the shallow center, whereas that formed near cation vacancy was suggested to be the origin of the intermediate deep center. The influence of the sample status (oxidized or reduced) on the UV-light-induced absorption was demonstrated to support our suggestion. Two different dark decay processes were associated with relaxations of holes from the shallow centers to two unequivalent Nb(Nb) adjacent to the doped cations at niobium sites.

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 LiNbO3 with various compositions. Bipolarons are considered to be responsible for the enhanced photovoltaic field in reduced near-stoichiometric LiNbO3, and their bulk photovoltaic constant kappa is estimated to be approximately 6.95 x 10(-32) m3/V. Q polarons (composed of two bipolarons) are introduced to explain the photorefractive effect of congruent LiNbO3 at both low and high light intensities.

We report on the observation of diffusion-dominant photorefraction and light-induced nonlinear forward and backward scattering in highly Mg-doped LiNbO3 at 351 nm. We also demonstrate what we believe to be the first continuous-wave self-pumped phase conjugation via stimulated photorefractive backscattering in the ultraviolet.

A new kind of optical novelty filtering by an incoherent light system is presented that is based on a special property of dynamic complementary suppression modulated transmission in bacteriorhodopsin film. By simplifying the energy system, we establish a theoretical model, and our experimental results are compared with those reached by numerical simulation of the novelty filter.

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.