Broadband optical radiation detector

Abstract

A method and apparatus for detecting optical radiation by optically monitoring temperature changes in a microvolume caused by absorption of optical radiation to be detected. More specifically, a thermal lens-forming material is provided which has first and second opposite, substantially parallel surfaces. A reflective coating is formed on the first surface, and a radiation-absorbing coating is formed on the reflective coating. Chopped, incoming optical radiation to be detected is directed to irradiate a small portion of the radiation-absorbing coating. Heat generated in this small area is conducted to the lens-forming material through the reflective coating, thereby raising the temperature of a small portion of the lens-forming material and causing a thermal lens to be formed therein. The thus-formed thermal lens is optically detected by irradiating the thermal lens by a collimated light beam. The light beam, after having passed through the thermal lens, is reflected by the reflective coating back through the thermal lens, and directed by a beam splitter to an optical detector. In a further embodiment of the invention, the optical radiation to be detected is passed through a template, thereby defining a plurality of areas on the radiation absorbing coating to be irradiated. A corresponding template is provided in a spread, collimated light beam to define a plurality of coherent light beams, each of which passes through a thermal lens in the lens-forming material. Each beam is then reflected by the reflective coating, passes back through the thermal lens, and is directed by a beam splitter to an optical detector. The invention is particularly useful as a broadband infrared detector.