Measurement of residual reflection at the interface between optically contacted components of microchip laser

We present a method for the measurement of a residual reflection at the interface between two optically contacted components of microchip laser. The method is based on the analysis of the reflection of a thermally scanned three-mirror Fabry-Perot interferometer (FPI). The microchip laser under test is illuminated with focused beam of a He-Ne laser, and is operated as a scanning interferometer by variation of its temperature. Imperfect optical contact leads to small reflection at the interface, which causes an amplitude modulation of the temperature response of the FPI reflection. The modulation depth is directly related to the reflection of the interface. The reflection coefficient of the interface is found from the measured modulation depth. Measurement results for microchips with sub-millimeter aperture size are presented. Residual reflection of 0.1-0.2% is determined.