US 11,740,217 B2
Method of determining nitrogen dioxide concentration with a tunable blue laser diode
Abdulaziz Aljalal, Dhahran (SA); Sameh Altanany, Dhahran (SA); Khaled Gasmi, Dhahran (SA); and Watheq Al-Basheer, Dhahran (SA)
Assigned to KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS, Dhahran (SA)
Filed by KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS, Dhahran (SA)
Filed on Aug. 6, 2021, as Appl. No. 17/396,364.
Application 17/396,364 is a continuation of application No. 16/789,692, filed on Feb. 13, 2020, granted, now 11,162,927.
Application 16/789,692 is a continuation of application No. 15/962,564, filed on Apr. 25, 2018, granted, now 10,613,067, issued on Apr. 7, 2020.
Prior Publication US 2021/0372981 A1, Dec. 2, 2021
This patent is subject to a terminal disclaimer.
Int. Cl. G01N 33/00 (2006.01); G01N 21/31 (2006.01); G01N 21/39 (2006.01); G01N 21/61 (2006.01)
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
OG exemplary drawing
 
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.