Process and device for analyzing traces of impurities in a gas sample by means of a diode laser

Device for analyzing traces of at least one impurity in a gas sample comprising,

• a semiconductor diode laser which emits a beam;
• at least one splitter system effective to split the beam emitted by the diode laser into at least two branched beams comprising, a measurement beam and a reference beam;
• a multipassage cell containing the gas sample to be analyzed;
• an optical device effective to send the branched measurement beam output by the splitter system along a measurement optical path onto the multipassage cell;
• a measurement photodetector which generates a signal;
• an optical device effective to direct the measurement beam output by the multipassage cell onto the measurement photodetector;
• a reference photodetector which generates a signal;
• a device effective to direct the reference branched beam output by the splitter system along a reference optical path onto the reference photodetector;
• element for acquisition and processing of the signals generated by the measurement and reference photodetectors;
• means for equalizing optical path lengths of the measurement and reference paths, respectively between the diode laser and the measurement photodetector, and between the diode laser and the reference photodetector, and
• supply current of the diode laser and means for modulating the supply current of the diode laser, effective to introduce a modulation comprising at least one function of the exponential type.