Effective utilization of quantum-cascade distributed-feedback lasers in absorption spectroscopy

摘要

A variable duty cycle quasi-cw frequency scanning technique was applied to reduce thermal effects resulting from the high heat dissipation of type I quantum-cascade lasers. This technique was combined with a 100-m path-length multipass cell and a zero-air background-subtraction technique to enhance detection sensitivity to a parts-in-10~(9) (ppb) concentration level for spectroscopic trace-gas detection of CH_(4), N_(2)O, H_(2)O, and C_(2)H_(5)OH in ambient air at 7.9 μm. A new technique for analysis of dense high-resolution absorption spectra was applied to detection of ethanol in ambient air, yielding a 125-ppb detection limit.