Low Power Quantum-cascade Laser Photoacoustic Spectrometer for Trace-gas Monitoring

The development of a novel type of highly sensitive multipass resonant PA cell for trace-gas detection enables the use of new compact low-power laser sources such as quantum-cascade lasers (QCLs) because the effective power present in the cell is increased by a factor of ~ 20 compared to a one-pass arrangement. Based on an existent mobile CO2 -laser photoacoustic (PA) spectrometer we implemented additionally a pulsed QCL with a tunable emission wavelength between 981.5 cm^-1 and 983.5 cm^-1 working near room temperature as pump source. Its average power is ≤ 1.7 mW and the laser-line width is < 0.2 cm^-1. With reference to HITRAN data a minimum measurable absorption coefficient α_min = 2.2×10^-5cm^-1 corresponding to a minimum measurable line intensity S_min = 2.5×10^-25 cm^-1/(molecule⋅cm^-2) is achieved even at the low QCL power. First measurements are presented to characterize the performance of our QCL based system.