Tunable diode laser absorption spectroscopy of common combustion gases at elevated temperatures

摘要

Abstract: Tunable diode laser absorption spectroscopy (TDLAS) shows promise for a number of environmental monitoring applications. This technique is advantageous over more classical methods because of excellent dynamic range, signal to noise ratios, and narrow bandwidth detection. With the rapid advances in the communications industry, lasers and optical components necessary for sensor technology are becoming affordable as well. One serious obstacle towards this effort is the paucity of spectroscopic data for the most useful, albeit weak, transitions near fiber optic communications wavelengths, especially at elevated temperatures. This data is important not only for species of monitoring interest, but also for those of possible interferants. In the near infrared, these are typically overtone and combination bands and hence accurate prediction of location, linestrength, and broadening coefficients is non-trivial. This is especially true for transitions arising from a highly excited rotational lower energy state. These are lines which may not be observable at room temperature but can play an important role for in-situ monitoring of a hot duct or smokestack. We have developed a system comprised of an extended cavity tunable diode laser and high temperature oven to characterize absorption spectra as a function of temperature and pressure. The experimental apparatus is described and data presented for water near 1.55 microns form 100 to 300 degrees C and 30 Torr. !0