We present photoacoustic (PA) spectroscopy measurements of carbon dioxide,
methanol, and ammonia. The light source for the excitation was a single-mod
e quantum cascade distributed-feedback laser, which was operated in pulsed
mode at moderate duty cycle and slightly below room temperature. Temperatur
e tuning resulted in a typical wavelength range of 3 cm(-1) at a linewidth
of 0.2 cm(-1). The setup was based on a Herriott multipass arrangement arou
nd the PA cell; the cell was equipped with a radial 16-microphone array to
increase sensitivity. Despite the relatively small average laser power, the
ammonia detection limit was 300 parts in 10(9) by volume. (C) 2001 Optical
Society of America.