REAL-TIME TRACE GAS SENSOR USING A MULTI-MODE DIODE LASER AND MULTIPLE LINE INTEGRATED CAVITY ENHANCED ABSORPTION SPECTROSCOPY

摘要

A highly sensitive trace gas sensor based on a Fabry-Perot semiconductor laser and cavity enhanced absorption spectroscopy is designed to be capable of measuring sub-ppb concentrations of trace gases in real time. The broad frequency range of the multi-mode Fabry-Perot semiconductor laser spans a large number of absorption lines of the species of interest enabling multiple line integrated absorption spectroscopy which improves the sensitivity of detection. Additionally, the broad wavelength range of the laser excites a large number of cavity modes simultaneously, thereby reducing the sensor's susceptibility to vibration and thermal fluctuations making it suitable for field based monitoring applications. Using a high finesse optical cavity also enhances the sensitivity of the sensor by providing large path lengths, on the order of kilometers, in a small volume. Relatively high laser power is used to compensate for the low coupling efficiency of a broad linewidth laser to the optical cavity.