Kenji Yoshizawa

20-W ultraviolet-beam generation by fourth-harmonic generation of an all-solid-state laser.

We have obtained UV power of 20.5 W with a repetition rate of 10 kHz by the use of a high-brightness high-power all-solid-state green laser and a high-quality CsLiB(6)O(10) crystal. This power is, to our knowledge, the highest UV power achieved so far in all-solid-state lasers.

Development of CO2 laser excited by 2.45-GHz microwave discharge

A new technique to excite a CO 2 laser by 2.45GHz microwave discharge is developed. Microwave plasma produced by the technique is so stable and homogeneous that any additional means to effectuate laser action such as fast circulation of laser gas and external magnetic field are not necessary. Utilizing the technique, a compact diffusion cooled CO 2 laser with 40cm active length is constructed. A magnetron available for microwave ovens is used as the power source of the laser. Average output power of 116W and maximum conversion efficiency of 18% in CW mode, peak output power of 1.2kW in pulse mode are obtained. Output beam with good focusibility is extracted by applying an unstable-waveguide hybrid resonator.

Gauss-core resonator: a novel stable resonator with a large-diameter diffraction-limited output beam.

A novel cavity design based on a stable resonator configuration is presented. The output coupler of the new stable resonator has a circular partial-reflection region in the center that is surrounded by an antireflection region. This resonator operates in a large-volume TEM(00) mode that is mainly determined by the partial-reflection region of the output coupler and is characterized by the use of an additional laser beam that is spread from the optical path in the cavity because of diffraction and is amplified by a laser medium. By combining part of a beam transmitted from the partial-reflection region with the amplified diffraction beam, a laser beam having a large diameter is obtained. A diffraction-limited output beam with the M(2) factor of 1.3 is obtained, as predicted theoretically when the new stable resonator is applied to a high-power cw CO(2) laser.

Novel stable resonator for large-volume TEM00 mode operation

A novel stable resonator is developed to realize stable operation at a TEM00 mode with a large beam diameter. The output coupler has a circular partial‐reflection region in the center surrounded by an antireflection region. The transverse mode is mainly selected by the partial‐reflection region. An amplified diffraction beam is extracted from the outer antireflection region. By combining part of the ‘‘core’’ beam transmitted from the partial‐reflection region with the amplified diffraction beam, a diffraction‐limited beam with the M2 factor of 1.3 is obtained from a high power continuous wave CO2 laser as predicted theoretically.

Disk‐shaped vacuum ultraviolet light source driven by microwave discharge for photoexcited processes

An efficient vacuum ultraviolet light source of large diameter has been developed for use in photoexcited processes. It has a novel structure in which microwaves propagating through a sapphire window break down Xe gas enclosed in a disk‐shaped volume and thereby produce intense emission from Xe at a wavelength of 147 nm. By optimizing the pulse width and the repetition rate, we obtained an illuminance of more than 3 mW/cm2 at the window surface. When this lamp was used as a source for photoinduced chemical vapor deposition of hydrogenated amorphous silicon films, a deposition rate of 5 nm/min was attained.

20-W, 10-kHz UV beam generation by an all-solid-state laser

Highest 266-nm UV power, to our knowledge, of 20-W was generated by an all-solid-state laser with a high-quality CLBO crystal.

Highly efficient diode-pumped 300-W Nd:YAG rod laser

Laser power of cw-329-W was generated with the optical efficiency of 41.1% and the electric efficiency of 18.8%. The laser also generated cw-118-W in TEM00 mode.

High-power UV beam generation by an all-solid-state laser

High-power all-solid-state UV lasers are used for precise material processing applications in industrial fields with the potential advantage in the maintenance cost compared with other UV lasers. In this paper we report on the evaluation of nonlinear crystals by high-power intracavity second harmonic generation, the evaluation of nonlinear crystals for UV generation by the transmission loss and the surface damage threshold measurements, and high-power UV beam generation up to 20 W with the repetition rate of 10 kHz.

Resonator technology for >100 W TEM00-mode operation in solid state lasers

Advanced resonator technology consisted of uniform pumping and bifocusing-compensation has been developed for rod- geometry laser-diode-pumped Nd:YAG lasers to generate laser power of > 100 W with the beam quality of M2 < 1.2 in cw mode. Experimental results are explained with wave- optics calculations.