Kana Fujioka

Growth and characterization of deuterated L-arginine phosphate monohydrate, a new nonlinear crystal, for efficient harmonic generation of fusion experiment lasers

L-arginine phosphate monohydrate (LAP) is a promising nonlinear organic crystal for higher harmonic generation in place of the conventional KDP. It has a large absorption at 1.06 μm. Deuterated LAP (DLAP) has been synthesized to decrease this absorption. The absorption coefficient was reduced from 0.09 to 0.02 cm -1 Microbes which easily multiply in the growth solution were successfully inhibited by Hadding H 2 O 2 . Damage thresholds of LAP and DLAP crystals are much higher than that of KDP and fused silica. We suggest that DLAP can be used in place of KDP in high power lasers.

Rapid growth over 50 mm/day of water-soluble KDP crystal

The rapid growth of KDP crystals was demonstrated at growth rates of up to 54 mm/day. Thermal and acoustic energy were used in the saturated solution to delete clusters of molecules. High supersaturations larger than 120% were achieved by overheating of the mother solution by 25 K. The application of acoustic energy to the solution was also used to achieve high supersaturation. The dissolution of the clusters in the solvent was discussed, explaining the rapid growth rates.

Optical properties of rapidly grown KDP crystal improved by thermal conditioning

Abstract The medium-size crystal (64 × 63 × 43mm) of potassium dihydrogen phosphate (KDP) was grown for one day from the 8 mm cubic seed crystal with a growth rate over 30 mm/day. The spectral transmittance, second-harmonic generation (SHG) property and laser damage threshold of the rapidly grown crystals were measured. The comparison with those of conventionally grown KDP crystal (2 mm/day) showed the prismatic sector included more impurities resulting in UV absorption. No difference was detected between the SHG properties. The lower laser damage threshold of the rapidly grown crystal was improved by a thermal conditioning to be 17 J/cm 2 of 1 ns pulse at 1 mm wavelength.

Preparation and optical properties of transparent Ce:YAG ceramics for high power white LED

Transparent Ce:YAG ceramics were synthesized from the Ce:YAG powder which was produced by co-preparation method of the hydroxides. The Ce:YAG ceramics exhibit a broad emission band peaked at 530 nm due to the 5d 4f transition of Ce 3+ . The transmittances of the samples obtained were 70 ~ 87 % at 800 nm. The absorption coefficient and emission intensity of Ce 3+ were increased with the increase of the thickness. With increasing thickness of the sample, the color coordinates of the Ce:YAG ceramics under 465 nm LED excitation shifted from the blue region to the yellow region with passing nearby the theoretical white point. The highest value of luminous efficacy of the white LED was 73.5 lm/W.

Effective Fluorescence Lifetime and Stimulated Emission Cross-Section of Nd/Cr:YAG Ceramics under CW Lamplight Pumping

Remarkable improvements in the lifetime of the Nd upper level and in the effective stimulated emission cross-section of Nd/Cr:YAG ceramics have been theoretically and experimentally studied. Until recently, it had been thought that the long energy transition time from Cr ions to Nd ions of Nd/Cr:YAG adversely affects laser action, degrading optical–optical conversion efficiency under CW and flash lamp pumping. However, current research showed that high-efficiency energy transition has a positive effect on laser action. The effective lifetime is increased from 0.23 to 1.1 ms and the emission cross-section is effectively increased to three times for that of the conventional Nd:YAG. A small signal gain is significantly improved, and the saturation power density is reduced to 1/10 that of the Nd:YAG for the same pumping power density. A CW laser light generated in a laser diode (LD)-pumped 1064 nm Nd:YAG laser oscillator was amplified, and the measured output power was saturated. The output laser power calculated using theoretical saturation power density was consistent with the experimental results.

A chromogenic limulus test for detection of microbes that decreases the laser damage threshold of potassium dihydrogen phosphate crystals

The chromogenic limulus test has been applied for the first time to detect an organic impurity contained in potassium dihydrogen phosphate (KDP) crystals. Impurities arise from microbes present during crystal growth, and are responsible for a reduced laser damage threshold. A sensitivity of 10 pg/g KDP (10−5 ppm) was achieved, provided that the KDP solution was neutralized to ∼pH 7. Endotoxin content in the prismatic region of KDP crystals grown in a microbe‐rich solution was approximately 100 pg/g KDP. The presence of an organic material in seemingly perfect KDP crystals could be experimentally confirmed.

Preparation of Transparent Ce3+:GdYAG Ceramics Phosphors for White LED

Transparent Ce:GdYAG ceramics were synthesized in the composition of (Gd Y0.999-Ce0.001)3Al5O12 using a co-preparation method of the hydroxides. The maximum value of parallel light transmittance of the sample was 80 % at 800 nm. The samples showed a broad emission band due to the 5d→4f transition of Ce3+. The emission peak wavelength red-shifted from 530 nm to 560 nm with increasing Gd content. The maximum QY values of the samples with different Gd concentration were 85 ~ 95 %. The color coordinates of the Ce:GdYAG ceramics based white LED located near the theoretical white point by optimizing the thickness. The Ra value improved from 65 to 81 with increasing Gd content.

Formation of macroscopic hillocks on the prismatic faces of KDP crystals due to microbes in the solution

Abstract The relation between macroscopic hillocks on the prisms of a KDP crystal and microbes identified in the mother liquor was investigated. A component of the microbes incorporated in KDP crystals was detected by chemical means. Its high concentration was found the prismatic region where many hillocks had formed.

INCREASE IN EFFECTIVE FLUORESCENCE LIFETIME BY CROSS-RELAXATION EFFECT DEPENDING ON TEMPERATURE OF Nd/Cr:YAG CERAMIC USING WHITE-LIGHT PUMP SOURCE

An increase in the effective fluorescence lifetime of Nd/Cr:YAG ceramics with temperature dependence was observed. The dependence on the doped Cr ion density for the increased effective fluorescence lifetime was also investigated. The effective lifetime of fluorescence in the ceramics increased from 1.1 to 1.8 ms owing to the phonon-assist cross-relaxation induced by the excited Cr ions, which is commonly observed in Tm:YAG or glass lasers. The increase in effective fluorescence lifetime can be explained by spontaneous emissions occurring from the excited Nd ions and excitations of the Nd ions from the lower level to the upper level at the same time. Additionally, an experiment for laser oscillations with the temperature of the laser material controlled was performed, and a remarkable increase of the output laser energy owing to cross-relaxation was observed when the temperature increased. The obtained maximum laser energy output was near twice that without cross-relaxation. The ceramics are considered promising lamp- or solar-pumped solid-laser materials owing to the efficient laser action based on this cross-relaxation.

Transparent Ce3+:GdYAG ceramic phosphors for white LED

Transparent Ce:GdYAG ceramics were synthesized from the oxide powder produced by a co-preparation method in the composition of (GdγY0.999-γCe0.001)3Al5O12. The sample showed transparency as high as 80 % at 800 nm. A broad emission band of Ce3+: 5d→4f transition shifted from 530 nm to 560 nm with increasing Gd content. The color coordinates (x, y) under blue LED excitation and quantum yield (QY) were evaluated with an integrating sphere. The color coordinates of the sample under blue LED excitation were increased with increasing thickness. By substituting Gd3+ for Y3+, the color coordinates also shifted to lower right and became closer to the Planckian locus in the chromaticity diagram. The red shift was explained by the energy change of 5d level of Ce3+ by the substitution of Gd3+for Y3+. With increasing excitation wavelength, the color coordinates of the γ=0 sample shifted from blue to yellow. This result is related to the shape of excitation band of the sample. The QY of the γ=0 sample was almost excitation wavelength independent in the range of 400 ~470 nm.