Yasuhiko Kuwano

Tetragonal vanadates YVO4 and GdVO4 – new efficient χ(3)-materials for Raman lasers

Abstract Efficient room temperature multiple Stokes and anti-Stokes picosecond generation in tetragonal YVO4 and GdVO4 host crystals for lasing trivalent lanthanides (Ln3+) has been observed for the first time. All measured stimulated Raman scattering (SRS) wavelengths in the visible and near infrared are identified and attributed to the SRS-active vibration modes of these vanadates.

β-barium borate single crystal grown by a direct Czochralski method

Abstract High purity single-crystal of β-BaB2O4 has been successfully grown from a BaB2O4 melt with the direct Czochralski method. The obtained crystal was confirmed to be that of the low-temperature β-phase by powder X-ray diffraction and the second harmonics generation. The growth rate was 0.6 mm/h, which is more than ten times as targe as that in the flux method. The growth direction was [001]. The present method requires to satisfy several important factors, such as choice of the starting material and temperature gradient at the growing point. The reason why a crystal of the low-temperature form is grown directly from a melt of the compound can be explained by the Ostwald step rule.

β-BaB2O4 single crystal growth by Czochralski method. II

Abstract The development of a Czochralski technique for the growth of high quality single crystals β-BaB 2 O 4 is reported. The β phase crystal could be directly grown from a BaB 2 O 4 composition melt without flux elements, although the β phase is metastable. The size of the grown crystal was extended to 15 mm in diameter and 40 mm in length. Neither cracks nor inclusions were observed. The effects of the preparation method of the starting material and the crystal growth conditions for obtaining the β phase single crystal were investigated. The relation between the β phase nucleation and the interfacial energy was discussed.

Temperature dependence and optimization of 970-nm diode-pumped Yb:YAG and Yb:LuAG lasers

We have investigated the temperature dependence of output performances for 970-nm diode-pumped Yb:YAG (Yb(3+):Y(3)Al(5)O(12)) and Yb:LuAG (Yb(3+):Lu(3)Al(5)O(12)) lasers over the wide temperature range from 80 to 310 K. Temperature-optimized operation was experimentally demonstrated at around 160 K and was theoretically confirmed by taking into account the absorption spectra change of Yb crystals at low temperatures. Cooling the crystal to below 160 K caused a narrowing of the absorption bandwidth and led to a decrease in output power and efficiency.

Effective distribution coefficient of neodynium in Nd:Gd3Ga5O12 crystals grown by the Czochralski method

Abstract The effective distribution coefficient k eff for Nd in Nd doped Gd 3 Ga 5 O 12 (Nd: GGG) crystals, grown by the Czochralski method, was determined over the concentration range 0.2–5.9 at% Nd in crystal. The Nd concentration in the crystal was measured by a fluorescent X-ray analysis to estimate the distribution coefficient. The k eff obtained showed a tendency to increase with increasing Nd concentration, relating to the homogeneity of the grown crystals. The optical absorption by Nd 3+ in the crystal at the 481.3 nm absorption peak was also measured. Using this method, the Nd concentration at the only homogeneous part of the crystal could be observed selectively. A value of k eff =0.41±0.02 was obtained by the optical method. The value obtained appeared to be independent of the Nd concentration in the initial melt.

Attaining 186-nm light generation in cooled ?-BaB 2 O 4 crystal

The transparency range of ??BaB2O4 (BBO) was expanded by means of cooling, and the resulting absorption coefficient at 193.4 nm was reduced to 0.29 cm-1 at 91 K from 1.39 cm-1 at 295 K.?Further, generation of light at 186.0 nm (the measurement limit in air) by type I sum-frequency generation (SFG) based on fundamental (744-nm) and third-harmonic (248-nm) light from a Ti:sapphire laser was confirmed for cooled BBO.?Calculations based on observed data for SFG wavelengths and phase-matching angles indicate a potential for cooled BBO to generate wavelengths as low as 181.7 nm.

β-BaB2O4 single crystal growth by Czochralski method using α-BaB2O4 and β-BaB2O4 single crystals as starting material

The effect of starting material crystal phase on β-BaB 2 O 4 Czochralski growth was investigated. As far as single crystals were used as starting materials, high quality β-BaB 2 O 4 single crystals were obtained, regardless of whether a- or /3-phase starting material was used. The nucleated polycrystalline blocks followed by the high quality β-BaB 2 O 4 single crystals had nearly horizontal structure, which ran along the (00-1) cleavage plane. The horizontal structure is indicative of the presence of structured melt.

Crystal growth and optical properties of Nd: GGAG

Neodymium-doped gadolinium gallium aluminum garnet (Nd: Gd3Ga5−xAlxO12, Nd: GGAG) has been grown by the Czochralski method. The transparent and optically good quality crystals were grown in the composition range form x = 0.1 to x = 2.0 and less than 2.5 at% neodymium concentration. The effective distribution coefficient for Nd in GGAG growth was 0.46. The refractive index at the 1.10 μm wavelength varied with the aluminum context x from 1.94 (x = 0.2) to 1.92 (x = 1.0). The results of stable and transient optical absorption measurements show that GGAG is applicable for use as a solid state laser material.

β-BaB2O4 phase-matching-direction growth by the Czochralski method

β-BaB 2 O 4 (BBO) phase-matching-direction growth was carried out by the Czochralski (CZ) method. Cylindrical BBO seed crystals, 4 mm in diameter and 25 mm in length, were used along the Nd:YAG laser-SHG, THG, and FHG phase-matching directions (θ = 22.8, 31.1, 47.6°). The tips of the seeds were tapered to 2.5 mm and etched with phosphoric acid at 100°C for 2 min. BBO crystals were pulled from a stoichiometric BaB 2 O 4 melt. The melt temperature was decreased at a fixed rate to avoid large temperature fluctuations at the growth interface. High-quality BBO crystals (15 mm in diameter and 70 mm in length) were grown along each of the phase-matching directions. This growth technique will contribute to the high-production yield of BBO crystals for nonlinear optical devices.

Refractive indices of YAlO3 : Nd

Refractive indices of YAlO3 : Nd (containing 1.0 at.% Nd) were determined in the 0.5–1.1‐μm wavelength range. The single‐term Sellmeier dispersion relation could be applied in the wavelength region between approximately 0.6 and 0.9 μm.