Ultraviolet divergence short distances. The name comes from the earliest example of such a divergence, the "ultraviolet catastrophe" first encountered in understanding blackbody radiation. According to classical physics at the end of the nineteenth century, the quantity of radiation in the form of light released at any specific wavelength should increase with decreasing wavelength—in particular, there should be considerably more ultraviolet light released from a blackbody radiator than infrared light. Measurements showed the opposite, with maximal energy released at intermediate wavelengths, suggesting a failure of classical mechanics. This problem eventually led to the development of quantum mechanics. The successful resolution of the
Photoacoustic effect added steady light does not produce any photoacoustic effect by itself, but changes the photoacoustic response due to the modulated/pulsed probing light. The resulting signal serves as a reference to all other measurements in absence of the background light. The photothermal part of the reference signal is maximal, since at photosynthetic saturation no energy is stored. At the same time the contribution of the other mechanisms tends to zero at saturation. Thus the reference signal is proportional to the total absorbed light energy. In order to separate and define the photobaric and photothermal contributions in spongy samples (leaves, lichens) one