Liquid detection by InGaAsP semiconductor diode lasers with multiple short external cavities (MSXC)

Summary form only given. We report a scheme of multiple short external cavities (MSXC) to force diode lasers to operate in modes spaced by up to 72 nm and the application of the MSXC laser to the detection of liquids. The mechanism of mode selection is to use two cavities, one to choose the mode enhancement region in the gain profile and one to confine the enhancement to a single mode. We used the MSXC lasers to detect water in acetone as a demonstration. The scheme combines the advantages offered by semiconductor lasers with the robust predictions of multivariate calibration.