Photoacoustic detection of nitric oxide by use of a quantum-cascade laser

A photoacoustic trace-gas sensor for the measurement of nitric oxide with a detection limit of 500 parts in 10(9) has been demonstrated. The radiation source was a thermoelectrically cooled distributed-feedback quantum-cascade laser operating in pulsed mode near 5.3 microm with an average laser power of 8 mW. A resonant photoacoustic cell was excited in its first longitudinal mode by the modulated laser light. Preliminary measurements have been performed to test the performance of our photoacoustic sensor; possible improvements to reach lower detection limits are discussed.