Environmental and chemical sensing applications of diode and quantum cascade laser based gas sensors

Summary form only given. In recent years, laser-based techniques for the real time detection of trace gases with ultra high sensitivity and excellent selectivity have been developed. In this paper, we report the development of portable automated gas sensors based on three different types of device architectures. If the anticipated concentration levels of a desired trace gas are sufficiently large and if this species exhibits near IR resolved rotational-vibrational transitions that are free of interfering species (such as CO/sub 2/ and H/sub 2/O), then a sensor based on distributed feedback (DFB) diode lasers are ideally suited. If, however, trace gas detection at ppb and ppt levels is required for a specific application, it is convenient to select a sensor architecture suitable for the mid-IR based on difference-frequency generation (DFG) of two diode lasers in a nonlinear optical material such as periodically poled lithium niobate or quantum cascade-DFB lasers in the 3 to 5 /spl mu/m and 4 to 17 /spl mu/m spectral region, respectively. In the case of the two types of diode laser DFG based gas sensors, we have used robust fiber pigtailed telecommunications DFB diode lasers and, when appropriate, Yb and Er/Yb optical fiber amplifiers to boost their power and fibered beam delivery. The QC-DFB based gas sensors have so far been operated either CW or pulsed, cooled to liquid nitrogen and room temperatures, respectively. Details of the spectroscopic parameters for the three spectroscopic devices will be reported, specifically their available power, linewidth, and wavelength tunability.