Photothermal spectroscopy with pulsed laser sources is developing into a powerful method for determining nonradiative, excited state quantum yields and decay kinetics of molecules in solution. The measurement is an example of photocalorimetry where the heat given off by the decay of excited states and/or photoproducts is observed as an increase in the sample temperature. Photoacoustic spectroscopy with a pulsed laser and a high bandwidth piezo electric transducer allows the time-dependence of the heat release from excited states to be measured directly with submicrosecond time resolution. The instrument signature on the heat signal for this method, however, is not ideal for determining the photoreaction kinetics of the sample due to acoustic resonances and lack of any low-frequency response.

The introduction of lasers into spectroscopic instrumentation has produced outstanding gains in detection compared with conventional light sources.