Fotoakustická spektroskopia

   Exemplary assembly of a photoacoustic spectroscopefor gas analysis with an acoustic cell.

Resonance ocours at a wavelength of double the resonator length. Instead of a chopper wheel, variation of the absorption could also be achieved with a tunable laser, modulating its frequency across absorption wavelength. Additional λ/4 tube elements could be added for example in the gas inlet to prevent unwanted flow noises. Electronic control elements, especially a lock-in amplifier, are not shown.

1. Light source (e. g. Laser)
2. Chopper wheel
3. semipermeable mirrors form an optical resonance system
4. cell windows (tilted for polarisation)
5. gas flow inlet and outlets
6. buffer gas volumes
7. acoustic sensor (e. g. microphone or transducer)
8. resonator