Sensitive and Compact Sensor Employing a Visible Diode Laser and A High Finesse Optical Cavity for Trace Gas Detection (NO2)

Apparatus for detecting trace species using multi-line absorption spectroscopy, comprising:

• a laser source that generates a broad energy laser beam, wherein the frequency of the laser beam can be matched with the absorption features of the species of interest;
• a high finesse optical cell with an off-axis input for receiving the laser beam and fitted with high reflectivity mirrors at the wavelength corresponding to the laser output frequency so as to generate a high density of transverse modes, and wherein the laser beam exiting the cavity contains information about the absorption spectra of multiple lines of the species of interest in the cavity;
• an off-axis paraboloidal reflector at the output of the cell arranged so that the laser beam exiting the cavity is focused;
• a low noise high gain detector that receives the focused laser beam from the reflector and measures the absorption spectra of the species;
• a storage medium for recording the measured absorption spectra from the detector;
• an integrator circuit that integrates the recorded detector signals of the absorption spectra over multiple lines of the absorption features of the trace gas;
• and
• analyzer circuit using the integrated detector signals to determine the concentration of the at least one trace gas of interest.