Patent ID: 9651488
Date: 2017-05-16
CPC Classifications: G01N,Y02A

Claim:
1. A method for detecting and measuring the concentration of a gaseous molecular species within an environment having an ambient temperature and an ambient pressure comprising: (a) providing a light source capable of providing an emitted mid-IR light whose wavelength may be caused to traverse across the wavelength range of a rotationally resolved absorption line of the gaseous molecular species; (b) providing a gas cell; (c) providing an optical system within an optical chamber module, said optical system for directing the mid-IR light from the light source into the gas cell so as to pass therethrough and be attenuated therein, for receiving the attenuated mid-IR light and spatially separating it from the directed mid-IR light and for detecting the attenuated mid-IR light; (d) providing temperature stabilization of the light source and the optical system, said providing of temperature stabilization including providing the light source and the optical chamber module within a thermally insulated enclosure; (e) providing a system for stabilizing the pressure of a sample gas flowing through the gas cell at a pressure less than the ambient pressure to within one torr (1 Torr); (f) providing a system for stabilizing the temperature of the sample gas flowing through the sample gas cell at a sample gas temperature greater than the ambient temperature to within one degree Kelvin (1° K); (g) causing the sample gas from the environment to flow through the gas cell and through the optical chamber module at the sample gas pressure and the sample gas temperature, wherein an internal volume of the gas cell and an internal volume of the optical chamber module are not isolated from one another; (h) operating the light source so as to cause the wavelength of the emitted mid-IR light to repeatedly traverse across the wavelength range of the rotationally resolved absorption line; (i) operating the optical system so as to cause the emitted mid-IR light to pass through and be attenuated by the sample gas in the gas cell and so as to cause the attenuated mid-IR light to pass to a photodetector of the optical system; (j) detecting the attenuated mid-IR light by the photodetector at each of a plurality of discrete data points, each data point corresponding to a respective wavelength during a wavelength traverse; (k) constructing a direct absorption spectrum of the rotationally resolved absorption line using the plurality of data points; and (l) determining the concentration of the gaseous molecular species from the direct absorption spectrum.