Quantum Cascade Laser Intracavity Absorption Sensor

A mid-infrared intracavity laser absorption spectrometer based on an external cavity multi-mode quantum cascade laser is combined with a scanning Fabry-Perot interferometer is used as tunable narrow band transmission filter to analyze the laser emission spectrum. Sensitivity as a trace gas detector at 8.1 micron wavelengths has been demonstrated based on a weak water vapor line at an absorption coefficient of 1 x 10(-5) cm(-1). For molecules of reasonably strong absorption cross section (10(-17) cm(2)), this corresponds to a detection limit of 40 ppb.