Abstract

In photothermal spectroscopy, the sample under investigation is excited with a modulated or pulsed light source [1]. Via radiationless decay part of the absorbed light is released in the sample as heat. With the incident energy being either modulated or pulsed, the heat generation will also show a corresponding time dependence. Thermal waves are, therefore, generated and, due to thermal expansion, acoustic waves are induced. These waves can be detected with suitable transducers, such as pyro- or piezoelectric transducers. With a pyroelectric thin film calorimeter recently, a sensitivity of nanojoules was obtained at a time resolution of tens of nanoseconds [2]. Only the absorbed and via radiationless decay into heat converted fraction of the incident light energy contributes towards the photothermal signal. The fact that the absorbed energy is determined directly and not as the difference of incident and reflected or transmitted light energy makes photothermal techniques particularly suitable for weakly absorbing samples, strongly scattering or opaque samples. Combined with laser excitation, this detection method, therefore, offers a unique combination of advantages, such as high sensitivity, high spectral resolution, high time resolution and instrumental simplicity.

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