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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