How does Tuneable Laser Diode Spectrometry work ?
TDLS is an infrared absorption measurement. Many gases have characteristic absorption bands in the infrared wavelength region. In a typical set-up, IR light from a light source traverses a cavity and falls onto a photo detector. Interaction of infrared light (absorption) with gas molecules in the cavity leads to a decrease of IR radiation intensity on the detector, depending on the gas concentration. The absorption bands of gases with relatively small molecules show a well resolved fine structure, consisting of many individual absorption lines. In TDLS, a single-mode tuneable diode laser is the light source for the gas measurement. Its wavelength is chosen to be centered onto one of the fine absorption lines of the target gas. The laser is then driven to scan this absorption line within a very narrow range (~2nm) to obtain the gas concentration. Typically one laser is used to measure one gas. Due to the sharpness of the lines (~ 0.1 nm) there is practically no cross-sensitivity with ot
