Use of diffuse reflections in tunable diode laser absorption spectroscopy:implications of laser speckle for gas absorption measurements

摘要

Abstract We report the effects of self-mixing interference on gas detectionusing tunable diode laser spectroscopy. For very weak feedback, the laser diodeoutput intensity gains a sinusoidal modulation analogous to that caused by lowfinesse etalons in the optical path. Our experiments show that self-mixinginterference can arise from both specular reflections (e.g. cell windows) anddiffuse reflections (e.g. Spectralon™ and retroreflective tape), potentially ina wider range of circumstances than etalon-induced interference. The form andmagnitude of the modulation is shown to agree with theory. We have quantifiedthe effect of these spurious signals on methane detection using wavelengthmodulation spectroscopy and discuss the implications for real gas detector