(DE19717145-A1)      In a selective process to identify gases in the near infra-red range, and to measure their concentration by narrow-band light absorption, the novelty is that the process consists of the following steps: (a) a distributed feed back (DFB) laser diode transmits near infra-red light along a measuring distance, which impinges on a photo-detector cell (2); (b) the DFB laser diode (1) is operated above room temperature and above 40 C; (c) one or more spectral lines of the gas in question are selected, the laser diode (1) being of a corresponding wavelength; (d) during spectral measurements, the laser diode temperature is adjusted, such that the spectral line to be identified is checked against the emission wavelength-dependent operating temperature; (e) the level and difference in absorption within the range of the spectral line, is evaluated to detect and ascertain the gas concentration. Also claimed is a suitable gas sensor.    USE -   To selectively detect the presence and concentration of gases esp. incorporating hydrogen atoms in e.g. safety or environmental applications, esp. methane.    ADVANTAGE -   The process and assembly detect the presence of selected gases to within finer tolerances and at higher reliability, lower cost and fewer service intervals than prior art assemblies.    (DE19717145-C2)      In a selective process to identify gases in the near infra-red range, and to measure their concentration by narrow-band light absorption, the novelty is that the process consists of the following steps: (a) a distributed feed back (DFB) laser diode transmits near infra-red light along a measuring distance, which impinges on a photo-detector cell (2); (b) the DFB laser diode (1) is operated above room temperature and above 40 C; (c) one or more spectral lines of the gas in question are selected, the laser diode (1) being of a corresponding wavelength; (d) during spectral measurements, the laser diode temperature is adjusted, such that the spectral line to be identified is checked against the emission wavelength-dependent operating temperature; (e) the level and difference in absorption within the range of the spectral line, is evaluated to detect and ascertain the gas concentration. Also claimed is a suitable gas sensor.    USE -   To selectively detect the presence and concentration of gases esp. incorporating hydrogen atoms in e.g. safety or environmental applications, esp. methane.    ADVANTAGE -   The process and assembly detect the presence of selected gases to within finer tolerances and at higher reliability, lower cost and fewer service intervals than prior art assemblies.