Photoacoustic spectroscopy

Photoacoustic spectroscopy is based on the photoacoustic effect. The discovery of the photoacoustic effect dates to 1880 when Alexander Graham Bell showed that thin discs emitted sound when exposed to a beam of sunlight that was rapidly interrupted with a rotating slotted disk. The absorbed energy from the sunlight is transformed into kinetic energy of the sample by energy exchange processes. This results in local heating and thus a pressure wave or sound. Later Bell showed that materials exposed to the non-visible portions of the solar spectrum (i.e., the infrared and the ultraviolet) can also produce sounds. By measuring the sound at different wavelengths, a photoacoustic spectrum of a sample can be recorded that can be used to identify the absorbing components of the sample. The photoacoustic effect can be used to study solids, liquids and gases.