CPC G01N 33/0037 (2013.01) [G01N 21/314 (2013.01); G01N 21/39 (2013.01); G01N 21/61 (2013.01); G01N 2021/3155 (2013.01)] | 7 Claims |
1. A blue laser based method for measuring a concentration of nitrogen dioxide in a gaseous mixture, comprising:
generating a multimode laser beam with a tunable blue laser diode having a nominal output wavelength of 445-455 nm with an output power of up to 50 mW at an injection current and a diode temperature;
splitting the multimode laser beam into a reference beam and a signal beam with a beam splitter optically coupled to the multimode laser beam at an incidence angle of 30-60°;
passing the signal beam through the gaseous mixture and recording a first voltage signal with a first detector;
passing the reference beam through a reference medium and recording a second voltage signal with a second detector;
measuring a transmittance of the signal beam at the injection current, wherein the transmittance is a ratio of the first voltage signal to the second voltage signal;
tuning the multimode laser beam by varying the injection current and repeating the splitting, passing the signal beam, passing the reference beam, and the measuring to form a transmittance spectrum, wherein the injection current ranges from 30 mA to 160 mA in a step of 10 mA;
measuring a column density of nitrogen dioxide in the gaseous mixture from the high transmittance spectrum; and
calculating the concentration of nitrogen dioxide in the gaseous mixture from the column density;
wherein the gaseous mixture is disposed in an elongated compartment having a length of 0.01-10 m and a first end and a second end,
wherein the first end and the second end each have a transparent window transparent to a UV light and/or a visible light,
wherein the transparent windows are tilted with an angle of 30-60° relative to a longitudinal axis of the elongated compartment, and
wherein each transparent window causes a loss of less than 1% of the intensity of the signal beam.
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