A visible-light semiconductor laser with an output of 40 mW at a 0.78-um wavelength, developed at hitachi Ltd.'s Central Research Laboratory, promises to fill the need for a light source for recording optical disks. It is to become available as a laboratory sample in september and in production quantities in March 1984. Contributing to the high output is a multilayer coating of alternate half-wavelength layers of silicon dioxide and amorphous silicon. Reflectivity is increased from 30% to 90%, with 95% of the laser's output directed out of the other end. The Japanese company says the coating will boost the output of existing lasers by 50%. also boosting the output is a strip waveguide under the active region, produced during fabrication of the self-aligned buried-strip heterojunction structure.