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) dealt with themes of anxiety and despair. Bono has described "Ultraviolet" as "an epic U2 song [but] the key of it left my voice in a conversational place and allowed a different kind of lyric writing." Producer Eno wrote that a combination of opposites within each song was a signature characteristic of "Achtung Baby" and that as part of that, "Ultraviolet" had a "helicopterish melancholy". In "Achtung Baby"s album package, "Ultraviolet" is presented next to a photograph of a crumbling Berlin building that has a Trabant parked in front of it. "Rolling Stone" noted that "Ultraviolet" was one of the