Photoacoustic Fourier Transform Infrared Spectroscopy (FTIR-PAS)

FTIR is a widely used method for obtaining IR spectra of a sample. The sample is exposed to IR radiation modulated by an interferometer and the intensity of transmitted radiation is monitored via an IR detector. At certain resonant frequencies characteristic of the specific sample, the radiation will be absorbed resulting in a series of peaks in the spectrum, which can then be used to identify the sample.

Gasera has improved the sensitivity of the gas phase FTIR significantly by combining FTIR and photoacoustic spectroscopy (FTIR-PAS). This technology can also be applied to solid, semi-solid and liquid samples.



Gas phase photoacoustic FTIR is based on the absorption of modulated light leading to the local warming of the absorbing volume element. The generated pressure waves are detected by a sensitive pressure detector producing a signal proportional to the absoption.

In comparison to an absorption spectrometer (conventional FTIR) a significantly smaller sample cell can be used. Therefore, small sample gas volumes are needed and the whole device is smaller. This makes it ideal for compact portable and hand-held instruments.

Short optical path length brings about other advantages, in particular the high linearity of response of the measured signal. Linearity is important for measuring the analyte response accurately and for accurately subtracting the signals from any interfering gases, in particular, from water and CO2. This feature is very important when measuring industrial exhaust gases, which usually contain high levels of water vapour.

The Gasera’s patented optical cantilever sensor provides huge dynamic range. This combined with the linear response opens up new interesting applications such as before and after analysis of scrubbers etc.

Furthermore, when using the novel silicon cantilever sensor, the sample cell can be heated up to 200°C, which is required in many industrial emission applications. As a result of these advantages, the photoacoustic technique has a high potential for the measurement of industrial emission gases, in all fields.