Low power quantum-cascade laser photoacoustic spectrometer for trace-gas monitoring

The development of a novel type of highly sensitive multipass resonant PA c ell for trace-gas detection enables the use of new compact low-power laser sources such as quantum-cascade lasers (QCLs) because the effective power p resent in the cell is increased by a factor of similar to 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 em ission wavelength between 981.5 cm(-1) and 983.5 cm(-1) working near room t emperature as pump source. Its average power is less than or equal to 1.7 m W and the laser-line width is < 0.2 cm(-1). With reference to HITRAN data a minimum measurable absorption coefficient <alpha>(min) = 2.2x10(-5)cm(-1) corresponding to a minimum measurable line intensity S-min = 2.5x10(-25) cm (-1)/(molecule.cm(-2)) is achieved even at the low QCL power. First measure ments are presented to characterize the performance of our QCL based system .