Laser diode photoacoustic detection in the infrared and near infrared spectral ranges

Abstract

A new technique for high resolution photoacoustic detection based on application of laser diodes has been developed. This method was tested and compared using identical photoacoustic instrumentation (cell and microphone) to study gas absorption in three different spectral regions, namely: the infrared range near 2100 cm⁻¹, CO and OCS fundamental band absorption; the ranges near 4200 and 4350 cm⁻¹, CH_4, NH₃ and N₂O overtone and combination band absorption; the near infrared range near 6500 cm⁻¹, CO, CO₂ and NH₃ overtone absorption. Several types of diode laser operating at room temperature or at liquid nitrogen temperature were compared. The optimum gas pressures for the maximum sensitivity of the photoacoustic signals were found and the detection limits were estimated for all of the gases studied. The best sensitivity was achieved for NH₃ at 100 ppbv. The sensitivity of the developed system was tested on detection of traces of NH₃ and CO₂ gases from car exhaust.