Abstract

Many continuously tunable lasers are now available in the infrared atmospheric transmission windows at 3-5 μm and 8-14 μm. As the power output of these devices is improved, the effect of detector noise on sensitivity becomes less important, and the limit to measurement accuracy is caused by unwanted interference from changing molecular constituents and changing pressure and temperature. In general, the best line for monitoring a particular species is not necessarily the strongest. This paper suggests a useful criterion for optimum line selection for a ratio-type derivative spectrometer.