Standoff Spectroscopy

Detection of chemicals from a distance has many applications. Our standoff chemical sensing is a variation of photoacoustic and mid infrared absorption spectroscopy of surface adsorbed species. The standoff photoacoustic technique is based on detecting surface adsorbed chemicals using a quantum cascade laser (QCL). The target surface is illuminated with a pulsed QCL. The reflected/scattered light is then collected using a telescope and focused on a microfabricated acoustic resonator to excite acoustic resonance. The pulsed light causes mechanical resonance in the detector since the pulse frequency of the QCL is matched with the acoustic resonance frequency of the detector. As the illumination wavelength is tuned, the response of the acoustic resonator varies in proportion to the absorption spectrum of the molecule. The resonance amplitude data of the detector is then processed to identify the surface adsorbed chemicals.