NOVEL ETALON FRINGE REJECTION TECHNIQUE FOR LASER-ABSORPTION SPECTROSCOPY

When used for trace-gas detection, laser absorption spectroscopy is usually limited by false absorption signals that are traceable to interferometric effects induced by windows and other pairs of optical surfaces. Here we introduce a new technique that can selectively reject these etalon fringes while preserving the true absorption signal over a wide range of etalon free spectral range to absorption linewidth ratios. We present a theoretical analysis and experimental verification by using a tunable lead salt diode laser.