Yoshio Kagebayashi

Long-term operation of CsLiB(6)O(10) at elevated crystal temperature.

We have successfully resolved the degradation problem of CsLiB(6)O(10) (CLBO) by means of elevated crystal temperature. CLBO crystals were continuously operated at 160 degrees C in ordinary room humidity. No degradation of performance was observed after more than 1 month. We believe that heating CLBO crystal above 130 degrees C can relieve stresses introduced by crystal hydration, cutting, polishing, and thermal shock owing to laser power absorption. Thus long-term operation of CLBO crystal is achieved for effective application of laser frequency conversion. Output stability from CLBO is also further enhanced at elevated crystal temperature.

K 2 AI 2 B 2 O 7 : a new nonlinear optical crystal

A new NLO crystal K2Al2B2O7 (Potassium Aluminum Borate, KAB) has been discovered. The material crystallizes in the Trigonal system with a equals 8.5669(8) Angstrom, C equals 8.467(1) Angstrom and Z equals 3, KAB possesses similar space arrangement of SBBO. KAB crystal with dimensions of 18 X 14 X 3 mm was grown by flux method. The optical properties of KAB was measured.

Crystal growth of cesium triborate, CsB3O5 by Kyropoulos technique

Large single crystals of CsB3O5 (CBO), free of cracks and inclusions, were successfully grown by the Kyropoulos technique from a slightly Cs2)-enriched melt. The growth conditions were experimentally established. Maximum dimensions obtained were 45×41×44 mm fora×b×c-axes. Optical uniformity of these as-grown crystals was verified by means of striation observation, and the optical transparency characteristic was measured in the region from vacuum ultraviolet (VUV) to infrared (IR) wavelengths.

Superior Properties of Cesium Triborate CsB3O5 for 194 nm Light Generation with Nd:Y3Al5O12 Laser

We compared the 194 nm output energy of a type-I phase-matched CsB3O5 (CBO) with that of a type-II phase-matched CsLiB6O10 (CLBO) crystal. Using CBO crystal, we generated deep ultraviolet light at 194 nm by sum-frequency conversion of 2 µm band light and 213 nm light at a conversion efficiency of 2.2%. We found that the conversion efficiency obtained using CBO was 2.7 times higher than that obtained using CLBO at a maximum input of fundamental light. We concluded that CBO is a superior nonlinear optical crystal for generating 194 nm light with Nd:Y3Al5O12 lasers because of its larger spectral and angular acceptance.

Refractive Index of CsB3O5 Grown by Top-Seeded Solution Growth

CsB3O5 (CBO) crystals were grown by the top-seeded solution growth (TSSG) technique from a slightly Cs2O-enriched melt. The measured refractive indices of the CBO crystals disagreed with the previously reported values by a factor of 10-2. The reason for the disagreement was speculated to be the difference in Cs concentration in the CBO crystal and/or impurity concentration. Single-term Sellmeiers equations for TSSG-CBO were used for measuring refractive indices. The phase-matching angles of harmonic and sum-frequency generations of Nd:YLiF4 lasers were calculated based on single-term Sellmeiers equations, and the phase-matching angle of second-harmonic generation was verified experimentally.

Design of a new technique for alleviating thermal dephasing of nonlinear optical crystal

A novel mechanism to alleviate the thermal dephasing of nonlinear optical crystal was developed. We named it temperature-profile compensation as defined from the in-situ temperature-profile measurement. Based on the concept of this mechanism, design on a technique for 3D temperature- profile compensation was demonstrated. By applying this technique on a CsLi B6O10 crystal, 10.6-W of 266-nm output power was obtained at 100-Hz. This result is 2.3-fold of that without alleviation. The conversion efficiency of 52 percent from the green is also more effective than the best result optimized at room temperature. Based on the similar concept, 1D temperature-profile compensation is also discussed for cases when the laser beam diameter reduced below approximately 2 mm. This is appropriate for frequency conversion of cw and diode-pumped kHz lasers. The design for 1D temperature-profile compensation can be very simple without involving any gas cooling.

Stable operation of CLBO crystal for laser frequency conversion at elevated temperature

CsLiB6O10 (CLBO) crystal1 has been a very effective nonlinear optical (NLO) crystal for fourth and fifth harmonics generation (4ω and 5ω) of Nd:YAG laser.2

High-energy, high-efficiency second-harmonic generation from a Nd-doped laser with high-quality CsB 3 O 5 crystal

Frequency doubling of high-energy Nd-doped laser emission yields harmonically converted laser energy (532-nm) of 1.2-J with 60 % conversion efficiency using a high optical quality top-seeded solution growth CsB3O5crystal.

Long-term operation of CsLiB/sub 6/O/sub 10/ crystal in fourth-harmonic generation of Nd:YAG laser

Long-term operation of fourth-harmonic generation by CLBO was evaluated by two types of lasers. One type of laser produces a high peak power beam at low repetition rate, and the other type of laser produces low peak power but can run at a high repetition rate. Using the high peak power laser, more than 1000 h of stable operation was observed. A group of microdamages resembling the incident beam was observed at the back surface of the CLBO, and the small decrease in output was attributed to it. The microdamage study showed that ion beam etching of CLBO surface was effective in avoiding the damage. When the etching depth was, e.g., 250 /spl Aring/ no power decrease, and no group of microdamages was recognized at the end of test (after 160 h operation).