A stable micro second harmonic generation (SHG) laser consisting of a diode- pumped Nd:YVO4 laser doubled by KTiOPO4 achieves 3 times higher storage density than usual on an erasable optical disk.

on When mini-solid-state lasers are end-pumped by diode lasers, it is important to have a good overlap between the pump beam and the oscillating mode and to have a pump spectrum that is narrow compared to the width of the absorption peak in the gain medium. We have theoretically studied the influence of the beam radius and the spectral width of the pump on the performance of diode-pumped devices. From the rate equations, the lasing threshold and the circulating intensity is evaluated numerically and the results can be used as a guideline in the design of intracavity doubling lasers. It is also shown that single-mode operation is more difficult when the pump spectrum becomes to wide.

Optical path analysis applying diffraction theory and geometrical ray tracing, and with collimation experiments shows that a hemiconic lens can convert the arc of blue radiation formed by Cerenkov second-harmonic generation to a parallel plane wave. To obtain an aberration-free plane wave, we modified the apex angle of the cone according to the birefringence of the waveguide. To correct chromatic aberration, we needed to have diode laser wavelength tuning with the aid of an achromatic cone lens doublet.

Many formats have been proposed and examined for next-generation DVD with a capacity of over 25 GB'). Disk mastering is necessary for this purpose, and optical disk cuttingmachines are key equipment for disk mastering. The laser wavelengths used in cuttingmachines are getting shorter as the density of disk memory increases. Now these wavelengths are shifting to the deep-UV (ultra-violet) range').In applying a deep-UV laser in a cutting-machine, there are two problems. One is the beam-pointing problem of the laser source. Usually Ar-SHG (second harmonic generation) lasers are chosen as laser sources for cutting-machines because of their reliability. A BBO (UBaB,04) is used as the SHG crystal in these lasers. As the BBO degrades during laser operation, it needs to be shifted to an unused area of the crystal. During the shift, the beam tilts more than 100 wad. In addition, changes of a few tens of Orad occur during daily laser operation because the phase-match angle of the BBO changes as the crystal is heated by the laser beam. Another problem is the absence of a dual-wavelength (deep-UV and redlinfrared) objective lens. An objective lens with different focal lengths for the cutting laser and the AF (auto-focus) laser would require changing or modifying the AF apparatus in current systems.Considering these problems, we developed a 257-nm cutting-machine with an automatic realignment system for the laser beam and an effective AF system for a non-dual wavelength objective lens. Figure 1 shows a block diagram of our cutting-machine. A 200-mW Ar-SHG laser is used as the laser source. The automatic realignment system consists of two sets of beamposition detectors and mirror actuators, and it is placed after the laser. An EOM (electric-optical modulator) is used as a noise-eater for each line, and a spatial filter is placed between AOM (acoustic-optical modulator) and AOD (acoustic-optical deflector) for wave-front correction. The AF system is mounted on a slider. Figure 2 shows the corrected beam pointing of the laser achived by using the automatic k. 0-7803-7379-0/02/$17.0002002 IEEE 30

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