LIGHT DETECTOR FOR THE NANOSECOND-DC PULSE WIDTH RANGE

摘要

A light detector consisting of a thin film of metallic (or conducting) material having an induced anisotropy in conjunction with means for establishing a temperature gradient in the film in a direction normal to the plane of the film is disclosed. When thin films of molybdenum and tungsten are excited by a pulsed laser light at normal incidence to the film, transverse thermoelectric voltages are generated. Output voltages across a 50 ohm load of 10 millivolts have been observed for an incident laser pulse of approximately 1 KW. Wave lengths in the range of 0.46-1.06.mu.m and pulse widths of approximately 3 to 300 nanoseconds produce output voltages. A correlation between intrinsic film stress and output voltage indicates that stress (one of induced anisotropy) in the metal film introduced during deposition or externally induced anisotropy such as can be produced by a magnetic field in magnetic materials gives rise to a nonscalar absolute thermoelectric power even though the metal films are usually considered to be isotropic in their transport properties. The output from the detector, in terms of polarity, may be reversed by reversing the direction of light incidence. Also, the direction and magnitude of the output may be controlled by adjusting the position of the metallic film relative to a pair of contacts disposed in sliding relationship with the metallic film. While not necessary to the practice of the present invention, an electrically insulating substrate is preferably used to cause a better temperature gradient normal to the plane of the film. In general, the response time of the films is dependent on the laser pulse width.