Photoacoustic spectroscopy

LED, laser or IR-emitter as light source

Depending on the target gas and application, different geometries of measuring cells and different light sources are selected. Cost-effective measurement systems that use rapidly modulatable LEDs as light sources, for example, can already determine target gas concentrations very sensitively (in the 1 ppm range). If lasers are used as light source, the selectivity and sensitivity of the measurement systems are improved, often reaching values in the low ppb range. 

Some examples:

For a compact SO₂ measurement system used for emission measurement in the exhaust gas scrubber on ships, Fraunhofer IPM employs a resonant measurement cell with a UV LED as light source. Thus, the required high resolution of 1 ppm in the measuring range up to 50 ppm SO₂ is achieved.

For a miniaturized photoacoustic CO₂ sensor used for the detection of indoor air quality, a non-resonant measuring cell was combined with a broadband IR emitter and a MEMS microphone. This allows a particularly small sensor with a sensitivity of 50 ppm and a wide measuring range up to 5000 ppm CO₂.

A laser-based PA module with a resonant measuring cell has been developed for detecting gas leaks, for example from gas pipes in the ground. The operation of the measuring cell is actively stabilized, and concentrations of methane (CH₄) and ethane (C₂H₆) are achieved with a resolution of a few ppb in each case.