Photoacoustic spectroscopy Photoacoustic spectroscopy Photoacoustic spectroscopy is the measurement of the effect of absorbed electromagnetic energy (particularly of light) on matter by means of acoustic detection. 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 light causes local heating, generating a thermal expansion which creates 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
Ultraviolet (Light My Way) singing the repeated "baby"s, one of the most heavily used clichés in pop songs and one that he had avoided up to that point in his songwriting; Flood later commented that "he got away with it alright." Although the song is ostensibly about love and dependency, like many U2 songs, it also lends itself to religious interpretations. Listeners have heard an allusion to the Book of Job and its tale of God serving as a lamp upon Job's head walking through the darkness. Robyn Brothers suggests that ultraviolet light is "a metaphor for a divine force both unseen to the