Internally Excited Acoustic Resonator for Photoacoustic Trace Detection

The quantum cascade laser can be used as an infrared source for a small portable photoacoustic trace gas detector. The device described here uses a quantum cascade laser chip without collimating optics mounted inside an acoustic resonator so as to use the full output power of the laser without the losses associated with optical components. The laser is positioned in the center of a longitudinal resonator at a pressure antinode and emits radiation axially along the length of resonator exciting an axially symmetric longitudinal acoustic mode of an open ended cylindrical resonator. Experiments are reported with an 8 ^Vm, quasi-cw modulated, room temperature laser used to detect N2O.