Cavity enhanced absorption spectroscopy (CEAS) technical overview
Optical absorption 
In an absorption instrument laser light is passed through a cell containing the sample gas and the wavelength is rapidly scanned across a selected absorption feature of the target molecule. The concentration of the target gas can be determined by measuring the changes in the laser light intensity. High specificity of measurement is gained by observing the sharp spectral features which can even be distinguished in the presence of complex backgrounds through use of narrow bandwidth diode lasers (typically in the near-infrared region).
Cavity enhanced technology
A disadvantage with conventional near infra-red absorption measurements is the limited path-length of a typical set-up. To increase detection sensitivity Avacta utilises cavity enhanced absorption methods where measurements are made using a high finesse optical cavity. By coupling the laser beam into a cavity the laser beam will typically pass through the gas sample more than a thousand times resulting in a dramatic increase in sensitivity.
Some other path length increasing cells do exist, however these typically only increase path length to around 200m at best and require a very precise optical setup (and are therefore sensitive to vibration during operation), or they require costly fast electronics and acousto-optic modulators. Conversely, Avacta’s CEAS technology achieves a several kilometre path length which is largely insensitive to vibration, and does not require costly high speed electronics.
Avacta are exploring joint development partnerships with gas detection sensor and systems manufacturers to incorporate the benefits of CEAS into their systems to improve performance, functionality, stability and reduce cost.
