We report on the development of a photoacoustic device for the detection of condensed-phase materials. A mid-infrared quantum cascade laser (QCL) was used for depth-profiling studies to distinguish among glycerol films and tetraethoxysilane (TEOS) films deposited on photoresist-coated silicon wafers. The QCL was continuously tunable from 1015 cm<sup>−1</sup> to 1240 cm<sup>−1</sup>, allowing for collection of photoacoustic vibrational spectra for these materials. Variation of the laser pulse repetition rate allowed for identification and molecular discrimination of glycerol, TEOS, and photoresist based solely on photoacoustic spectra collected at different film depths.

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