Coherent detection of the light backscattered by an optical surface

Abstract

We measured very low light power backscattered by optical surfaces using low coherence interferometry. The backscattered light can indeed be a critical noise source for interferometric gravitational wave detectors such as LISA, the laser interferometer space antenna developed by ESA, with the support of NASA and European national space agencies. We present the preliminary measurement results of light backscattered from a silver mirror and a bare N-BK7 window 1 mm thick using a superluminescent diode centered at 1060 nm as broadband light source. The use of low coherence interferometry allows light backscattered by both sides of the N-BK7 window to be recorded independently with a noise floor of around -110 dB.