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Abstract

A technique for extracting the impulse response of a sample of interest includes corresponding measurements made with the sample of interest and a reference sample. At each of a series of steps in an FT-IR spectrometer, the sample of interest is illuminated with an excitation pulse of infrared radiation, acoustic signals having a time dependence o.sub.S (t) arising from the excitation pulse are captured, and a Fourier transform O.sub.S of o.sub.S (t) is computed. At each of a series of steps in the FT-IR spectrometer, the reference sample is illuminated with an excitation pulse of analytic radiation, acoustic signals having a time dependence O.sub.R (t) arising from the excitation pulse are captured, and a Fourier transform O.sub.R of o.sub.R (t) is computed. For each step, an inverse Fourier transform of the ratio O.sub.S /O.sub.R is computed to provide a series of values s(t.sub.i) for a series of times t.sub.i. These values s(t.sub.i) represent the impulse response s(t) of the sample of interest for the mix of optical frequencies for that retardation value. Interferograms are processed to provide photoacoustic spectra.

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