Akira Fujinoki

Temporal compression by stimulated Brillouin scattering of Q-switched pulse with fused-quartz and fused-silica glass from 1064 nm to 266 nm wavelength

We have designed a compact solid compressor by stimulated Brillouin scattering (SBS), which consists of two right angle prisms and a fused silica glass block. A 13–16 ns Nd:YAG laser pulse has been temporally compressed to 1 ns or less phase conjugation pulse in a fused-quartz and fused-silica glass at four different wavelengths. Maximum reflectivity of SBS was 90–95% without damage. The brightness of the compressed pulse was about ten-fold higher than that of the incident pulse. Damage-free operation using fused quartz glass as a better phase conjugation material could lead to the construction of a more compact, laser-diode-pumped, and all-solid-state laser system.

Development of Nd-doped Optical Gain Material Based on Silica Glass with High Thermal Shock Parameter for High-Average-Power Laser

This paper reports demonstrations of laser amplification and oscillation at 1.06 /spl mu/m in a bulk-type Nd-doped silica glass (Nd/sub 2/O/sub 3/: 1.25 wt%, Al/sub 2/O/sub 3/: 2.72 wt%, SiO/sub 2/: 96.03 wt%) with a high thermal shock parameter, 12.0 W/cm.

40J class laser oscillation of Nd-doped silica glass with high thermal shock parameter

The authors demonstrated a 40J class laser oscillation from a bulk-type Nd-doped silica glass with a high thermal shock parameter. A maximum output energy of 37.3J was obtained from a laser oscillator that consisted of a 30% output coupler with a 30mm diameter and 300mm length laser medium. The thermal shock parameter, a figure of merit for the thermal toughness of the materials, was estimated to be 12.0W∕cm, which is 1.5 times larger than neodymium-doped yttrium aluminum garnet (7.9W∕cm). These results show that the Nd-doped silica glass has the potential to be installed in high-average-power or high-peak-power lasers.

Temporal Compression by Stimulated Brillouin Scattering of Q-switched Pulse with Fused Quartz Glass

An 8 ns Nd:YAG laser pulse has been temporally compressed to a 1 ns or less phase conjugation pulse in a fused quartz glass at three wavelengths. Maximum reflectivity of SBS was 40–45% without damage. The brightness of the compressed pulse was about fourfold higher than that of the incident pulse. Damage-free operation using fused quartz glass as a better phase conjugation material could lead to the construction of a more compact, laser-diode-pumped, and all-solid-state laser system.

Fused-quartz glass with low optical quality as a high damage-resistant stimulated Brillouin-scattering phase-conjugation mirror

Fused-quartz glass is found to be an ideal medium for high-power stimulated Brillouin-scattering experiments, because it gives a high reflectivity of over 95% at an incident energy of 2.3 J, has pulse duration of 16 ns, and has excellent fidelity in phase conjugation. The low optical homogeneity of the fused-quartz material selected resulted in a low focusability at the focus, resulting in a reduction in laser-damage occurrence, even in high-energy operations. Despite this fact, its conjugation fidelity is good for cancellation as a phase-conjugated mirror. All solid-state lasers with high-beam qualities, based on phase-conjugated mirrors with fused-quartz glass are highly suitable for use as laser sources in many applications.

Laser Oscillation of Nd-Doped Silica Glass with High Thermal Shock Parameter

Laser oscillation with the input/output characteristics of bulk-type Nd-doped silica glass with a high thermal shock parameter was demonstrated for the first time. The thermal shock parameter was estimated to be 12.0 W/cm, which is 1.5 times larger than that of Nd:YAG crystal (7.9 W/cm). The maximum output energy of 154 mJ was obtained with an output mirror of 20% transmittance. Although the output energy was 154 mJ, if without loss, output energy increases up to 1.69 J, eleven times larger than the present state. These results mean that Nd-doped silica glass can work as a high-average or a high-peak-power-laser.

Compact Temporal-Pulse-Compressor Used in Fused-Silica Glass at 1064 nm Wavelength

We have designed a compact solid compressor by stimulated Brillouin scattering (SBS) consisting of two right-angle prisms and a fused-silica glass block. A 13 ns Nd:YAG laser pulse was temporally compressed to a 1.2 ns phase-conjugated pulse in fused-silica glass at a 1064 nm wavelength. The maximum reflectivity of the SBS was over 95% without optical damage. The compressed pulse brightness was about 10-fold higher than that of the incident pulse.

Homogeneous TiO2–SiO2 Ultralow-Expansion Glass for Extreme Ultraviolet Lithography Evaluated by the Line-Focus-Beam Ultrasonic Material Characterization System

A TiO2–SiO2 glass ingot was fabricated by the soot method and homogenized by the zone-melting method. Elastic homogeneities of specimens prepared at different production stages were evaluated by measuring leaky surface acoustic wave (LSAW) velocity VLSAW using the line-focus-beam ultrasonic material-characterization system at 225 MHz. The homogeneous VLSAW distribution was within ±1.13 m/s, corresponding to a variation of the coefficient of thermal expansion (CTE) of ±5 ppb/K, and no striae were observed. VLSAW changes associated with residual stress inside the ingot could be detected. The relationships among VLSAW, TiO2 concentration, density, CTE characteristics, and fictive temperature were investigated. We found the possibility for extremely homogeneous TiO2–SiO2 glass with zero-crossing in CTE at a desired room temperature.

Smoothing of surface of silica glass by heat treatment in wet atmosphere

The effect of heat treatment on the surface morphology of fused silica glass substrates was investigated. It was found that the water vapor pressure during heat treatment had a strong influence on the flattening of the silica glass surface. The surface of the frosted glass changed into a transparent and lustrous surface after heat treatment with water vapor at 1200 °C for 48 h, whereas surface irregularities remained for heat treatment under a dry atmosphere. It was suggested that the difference in surface flattening was caused by changes in surface viscosity that depended on the concentration of OH groups on the surface. In order to quantitatively understand the effect of the heat treatment atmosphere, power spectral density (PSD) analysis and a novel peak and valley method were applied to the experimental results. From the PSD analysis, it was found that the Mullins’ model could not explain the smoothing behavior by heat treatment. The peak and valley method, which could separate the surface morphology ...

Development of Nd-doped optical gain material based on silica glass with a high thermal shock parameter for high-average-power laser

This paper reports demonstrations of laser amplification and oscillation at 1.06 /spl mu/m in a bulk-type Nd-doped silica glass (Nd/sub 2/O/sub 3/: 1.25 wt%, Al/sub 2/O/sub 3/: 2.72 wt%, SiO/sub 2/: 96.03 wt%) with a high thermal shock parameter, 12.0 W/cm.