Abstract: A mechanism for holding a substrate on a substrate stage of a substrate treatment apparatus according to the present invention comprises an exhaust mechanism section connected to the substrate treatment apparatus having the substrate stage therein and used to discharge a gas from the substrate treatment apparatus by suction, and a holding mechanism section having one end portion formed with a plurality of intake holes opening in the upper surface of the substrate stage on which the substrate is placed and the other end portion connected to the exhaust mechanism section, whereby the sucking force of the exhaust mechanism section is caused to act on the intake holes so that the substrate is held on the substrate stage by suction.

Abstract: An SHG device wherein a channel is formed on a part of a waveguide layer; and the thickness of the waveguide layer is set so that the refractive index of the channel for a fundamental is greater than that for an SH (second harmonic) and the refractive index of portions on the both sides of the channel for the SH is greater than that for the fundamental, thereby accomplishing the phase matching between the fundamental and the SH, which satisfies the conditions that an output power of 2 mW or more which is sufficient for reading signals from an optical disk, that the optical intensity distribution at a light emitting end has a single peak, that the optical spot diameter at a light emitting end is small enough, and that the wavelength of the output is in the blue region.