Abstract: Disclosed is an optical head comprising a light source for emitting a light beam having a predetermined wavelength, a light source driving part for driving the light source, a monitor light detector for detecting the light amount of the light beam emitted from the light source, an objective lens for collecting the light beam on a predetermined position of the optical disc, a light receiving element for receiving the light beam reflected from the optical disc so as to convert the received light beam into an electric signal, a base having an open portion and holding an optical member for guiding the light beam in the open portion in a manner to form an optical path of the light beam ranging from the light source to the objective lens, and holding means for holding the monitor light detector within the open portion in parallel to the optical path so as not to interfere with the light beam.

Abstract: A process for producing a protective layer or a primer layer for a heat-generating resistor for a thermal head by sputtering using a target comprising a sinter of a silicon nitride/silicon dioxide/magnesium oxide powder. By regulating the particle diameter of the powder, the target is prevented from suffering partial peeling during the sputtering.