Bingkun Yu

Femtosecond laser-induced oriented precipitation of Ba 2 TiGe 2 O 8 crystals in glass

Ba(2)TiGe(2)O(8) crystals were selectively precipitated on femtosecond laser irradiated BaO-TiO(2)-GeO(2) glass surface. Furthermore, the crystal could grow from the surface of glass to the interior towards the laser movement direction when the laser focus was continuously moved. The laser-induced crystal was confirmed to be Ba(2)TiGe(2)O(8) phase by x-ray diffraction analysis and micro-Raman spectra. We also observed blue light due to double-frequency conversion of the 800nm incident laser in the crystallized regions. We propose the observed phenomena resulted from the femtosecond laser-assisted orientation of precipitation of crystal.

Backscatter laser depolarization studies of simulated stratospheric aerosols: Crystallized sulfuric acid droplets

The optical depolarizing properties of simulated stratospheric aerosols were studied in laboratory laser (0.633 microm) backscattering experiments for application to polarization lidar observations. Clouds composed of sulfuric acid solution droplets, some treated with ammonia gas, were observed during evaporation. The results indicate that the formation of minute ammonium sulfate particles from the evaporation of acid droplets produces linear depolarization ratios of delta approximately 0.02, but delta approximately 0.10-0.15 are generated from acid droplet crystallization effects associated with recycled aerosols and the introduction of ammonia gas into the chamber. It is concluded that partially crystallized sulfuric acid droplets are a likely candidate for explaining the lidar delta approximately 0.10 values that have been observed in the lower stratosphere in the absence of the relatively strong backscattering from homogeneous sulfuric acid droplet (delta approximately 0) or ice crystal (delta approximately 0.5) clouds.

Study of crystal formation in borate, niobate, and titanate glasses irradiated by femtosecond laser pulses

The generation of nonlinear optical functional crystals in borate, niobate, and titanate glasses that have been irradiated by 800-nm femtosecond laser pulses was investigated by Raman spectroscopy. The effects of the length of irradiation time on the generation of crystals were measured. We show that the structure of the glass network was destroyed during irradiation by the femtosecond laser. (B3O6)3−, (NbO6)7−, and (TiO4)4− anion units as well as β-BaB2O4, LiNbO3, and Ba2TiO4 crystals were formed in the focal area of the irradiation. We suggest that femtosecond laser irradiation can be a useful approach to the fabrication of integrated optical devices.

Microprobe of structure of crystal/liquid interface boundary layers

The molecular structures and its evolutive regularities within the boundary layers in the crystal growth of KDP and DKDP have been studied in real time by using holography and Raman microprobe. The experiments show that the molecular structure of mother solution within the boundary layers is distinctly different from that of the solutions alone. In this paper, the effects of cations within the boundary layers on the structure of solution are considered. Within the characteristic boundary layers, the effects of cations cause the changes in O-P-O bond angle, electronic density redistribution of the phosphate groups, and significant changes in the bond intensity, thus leading to the breaking of partial hydrogen bonds of the phosphate associations, the readjustment of geometry of anionic phosphate groups and desolvation, and the forming of the smectic ordering structure of the anions-cations. Finally, the crystallization unit of anion-cation should be formed at the proximate interface.

Microstructure of the crystals generated in borate glass irradiated by femtosecond laser pulses

This paper deals with the microstructure of the generated crystals in borate glass by femtosecond laser irradiation, Raman spectroscopy was used to study the distribution of the two phases of barium metaborate crystals produced.