Soft modes in ferroelastic LaP5O14 and NdP5O14

We have observed an underdamped, temperature dependent optical phonon in the non-polar ferroelastic compounds NdP₅O₁₄ and LaP₅O₁₄. These materials exhibit a second-order displacive phase transition from C_2h to D_2h point group symmetry at temperatures slightly above ambient. The soft mode is observed in both phases.     

Photorefractive two-step recording in a piezoelectric La3Ga5SiO14 crystal doped with praseodymium

The first experimental verification to the authors' knowledge of efficient two-step recording in a photorefractive and piezoelectric crystal of La(3)Ga(5)SiO(14):Pr(3+) with cw laser light (I<20W/cm(2)) is reported. We found nonlinear behavior of the photorefractive sensitivity and photovoltaic current, indicating that the excitation process is connected to excitation of 4f(2) electrons of the Pr(3+) dopant through an intermediate level to the conduction band. This two-step nature of the photorefractive effect makes the crystal an exciting new candidate for applications in holographic storage.     

Laser-induced damage and periodic stripe structures of a CaF_2 single crystal by an ArF excimer laser

The laser-induced damage threshold of a calcium fluoride(CaF2)single crystal was obtained by a 193 nm ArF excimer laser.The damage morphology of the crystal was analyzed.The results showed that the surface of CaF2 single crystal broke along the natural cleavage plane under ArF excimer laser irradiation,some fragments fell off,and Newton’s rings were observed on the curved fragments.Laser-induced periodic stripe structures(LIPSS)appeared on the surface layer beneath the fragments that peeled off.The spacing of LIPSS was measured,and the formation mechanism of LIPSS was analyzed based on the interference model.     

Laser site-selection time-resolved spectroscopy of NdP5O14

Laser site-selection spectroscopy shows the presence of Nd ions in non- equivalent crystal field sites in NPP. Time-resolved spectroscopy indicates that energy transfer does not take place between ions in these different types of sites.     

Analysis of periodic thin-film structures with rectangular profiles

A rigorous analysis is presented for thin-film structures on which a rectangular-profile grating layer is superimposed. Typical dispersion curves are calculated for guided leaky waves, which are relevant to beam couplers in integrated-optics applications.     

Dynamic analysis of periodic structures

The natural vibration analysis of a periodic structure with repeated identical substructures may be simplified by using some symmetrical properties of the substructure dynamic matrices, resulting in a set of linear difference equations in the displacements. These equations are readily solved for cyclic symmetric systems, simply supported systems and infinite systems. The order of the overall frequency equations is at most equal to one half of the total number of degrees of freedom retained for a single substructure regardless of the number of substructures in the system. With these natural modes, the system with general boundary conditions at end stations is analyzed by a fast converging method.     

Laser emission from polished NdP5O14 crystals with directly applied mirrors

We report on crystal processing, laser fabrication, emission spectra and output characteristics of neodymium pentaphosphate lasers. We obtained cw oscillation with an output power of 19 mW from a crystal with dielectric mirrors directly applied on polished (001) planes. We pumped longitudinally with 280 mW of an argon ion laser at 514 nm focussed to a 94-μm diameter. Near threshold our laser operated in the vicinity of 1053 nm; when pumped 1.6 times threshold it operated dominantly in the vicinity of 1063 nm.     

Self-organized periodic photonic structure in a nonchiral liquid crystal

A hybrid-aligned cell of the smectic A liquid material 8CB gives two stable director configurations, one of which is periodic and gives strong diffraction of light. This photonic lattice director profile arises from "frustration" caused by conflicting constraints imposed by the boundary conditions and the constant amplitude smectic density wave. A model is proposed which accords well with the experiment results, predicting correctly the dependence of the periodicity on the cell thickness and reproducing optical polarization microscopy results.     

Efficient 355-nm generation in CsB3O5 crystal

We demonstrate UV generation in CSB3O5 (CBO) crystals grown by the top-seeded solution growth technique. 355-nm UV light was generated by use of a type II CBO crystal as a sum frequency of the fundamental light and the second harmonic of a nanosecond Nd:YVO4 laser. A 3.0-W output of the third-harmonic was obtained at a repetition rate of 31 kHz. The conversion efficiency from the fundamental light to the third harmonic reached 30%, which was 1.5 times higher than that obtained with a type II LiB3O5 crystal under the same experimental conditions.     

Diffusion in quasi-one-dimensional structures with a periodic sharp narrowing of the cross section

The problem of diffusion of particles in a tube with periodically positioned partitions with circular orifices at the center of each was considered. Using an approach based on the methods and results of the theory of diffusion-controlled reactions and the idea of homogenization of the permeability of partitions, we derived a formula for the effective diffusion coefficient for the steady-state regime of the process. The accuracy and applicability domain of the formula were determined by comparing its predictions with computer simulation results.     

The decay of low-frequency elastic oscillations in a Ba2NaNb5O15 crystal

The internal friction and shear modulus of a barium sodium niobate crystal were studied using the torsion pendulum technique at a frequency of ～25 Hz in the temperature range from 80 to 800 K. An internal friction relaxation peak of the domain nature was observed at 228 K. A relaxation process responsible for this internal friction peak is explained through compensation of the electric charge (induced by a piezoelectric effect at the 180° domain walls) by charged point defects diffusing toward the domain walls.