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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 and through thermal expansion 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. A photoacoustic spectrum of a sample can be recorded by measuring the sound at different wavelengths. This spectrum can be used to identify the absorbing components of the sample. The photoacoustic effect can be used to study solids, liquids and gases. 〔David W. Ball (''Photoacoustic Spectroscopy'' ) Spectroscopy, Volume 21, Issue 9, Sep 1, 2006〕 ==Uses and techniques== Photoacoustic spectroscopy has become a powerful technique to study concentrations of gases at the part per billion or even part per trillion levels.〔 Modern photoacoustic detectors still rely on the same principles as Bell’s apparatus; however, to increase the sensitivity, the following modifications have been made: # Use of intense lasers instead of the sun to illuminate the sample since the intensity of the generated sound is proportional to the light intensity; this technique is referred to as "laser photoacoustic spectroscopy" or "LPAS" # The ear has been replaced by sensitive microphones. The microphone signals are further amplified and detected using lock-in amplifiers. # By enclosing the gaseous sample in a cylindrical chamber, the sound signal is amplified by tuning the modulation frequency to an acoustic resonance of the sample cell. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Photoacoustic spectroscopy」の詳細全文を読む スポンサード リンク
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