Abstract: A method of calorimetric absorption spectroscopy (CAS) is claimed, wherein a sample, irradiated with a measuring-light pulse of a specified power, duration, and wavelength and whose absorbance at the specific wavelength of the measuring light is determined as a result of the heating of the sample which occurs as a result of the absorption of a portion of the measuring light, is cooled to a temperature which is so low that the specific heat of the sample during measurement is only a small fraction of the value at normal temperature. This produces an increase in sensitivity by a factor of more than 10.sup.5. The manner in which the lifetime of radiant and nonradiant recombination can be determined in a simple fashion is claimed for samples which have a first impurity center, capable of recombination both by radiation and without radiation, and a second center, capable of recombination only without radiation.