Optical Generation and Detection of Acoustic Pulse Profiles in Gases for Novel Ultrasonic Absorption Spectroscopy

We demonstrate a new all-optical, frequency-multiplexed, and fast technique for gas-phase ultrasonic absorption spectroscopy. A pulsed laser produces a short-duration acoustic pulse in the gas sample, and the acoustic pulse profiles at two distances are monitored by focused continuous probe beams. Fourier decompositions of these probe deflection signals provide the absorption spectrum, and examples for C${\mathrm{O}}_2$ and a C${\mathrm{O}}_2$+${\mathrm{H}}_2$O mixture are given. Ultrasonic propagation speeds in the megahertz regime are also obtained for several gases.