Photothermal FT-IR spectroscopy: A step towards FT-IR microscopy at a resolution better than the diffraction limit

We have used a miniaturized Wollaston wire resistive thermometer as a probe to record infrared absorption spectra of polymeric samples by detecting ph otothermally induced temperature fluctuations at the sample surface. This m ethod opens the way to absorption Fourier transform infrared spectroscopy/m icroscopy with a spatial resolution that is no longer diffraction limited, but is determined instead by the size of the contact between probe and samp le. At present, this is on the order of a few hundred nanometers. The therm al probe, of a type used in scanning thermal microscopy and microthermal an alysis, allows us to detect the photothermal response of a specimen exposed to the beam of a Fourier transform infrared spectrometer and heated thereb y. The signal from this probe measures the resulting temperature fluctuatio ns, and thus provides an interferogram which replaces the interferogram nor mally obtained by means of direct detection of the IR transmitted by a samp le.