Photoacoustic spectroscopy with emphasis to application on solid and powered samples

The peculiarity of photoacoustic (PA) spectroscopy is that, unlike other spectroscopic techniques (e.g UV that is always based on transmission spectra), it is concerned with nonradiative deexcitation processes that takeplace upon absorption of modulated light by the sample and subsequent thermal transfer processes to the surrounding. The effect was originally discovered by A. G. Bell in 1880, who focused an intermittent beam of radiation onto thin discs of various materials. Placing his ear against the discs he could hear "musics" from, by him called, the "Photophone". Soon afterwards, repeating Bell's experiments, Rayleigh and Preece tried to provide first theories for the observed effect. Rayleigh (1881) attributed this effect to the bending of the disc caused by unequal heating, while Preece (1881), who used a sonometer instead of the ear, stated that thephenomenon was purely an effect of radiant heat which occured because of volume changes in vapours and gases produced by the degradation and absorption of this heat in a confined space. Basically, this was the firsttheory in accordance with today accepted Rosencwaig's view (1980). Röntgen (1881,1881 a) performed the same experiments by intermittent radiation of gases and concluded that the phenomenon was caused by heating and expansion produced by absorption, and the subsequent cooling and contraction of the absorbing body. Similar experiments on vapours and gases were also done by Tyndall (1881,1889), who summarized his experiments in tables in which he placed various vapours and gases according to their decreasing ability to produce heat. [...