A gas sensor system is provided, comprising: a gas cell operable so as to receive a sample gas; a vacuum system fluidically coupled to the gas cell operable to maintain the sample gas within the gas cell at a sub-ambient pressure; a pressure sensor operable to sense a pressure of the sample gas; a t
A gas sensor system is provided, comprising: a gas cell operable so as to receive a sample gas; a vacuum system fluidically coupled to the gas cell operable to maintain the sample gas within the gas cell at a sub-ambient pressure; a pressure sensor operable to sense a pressure of the sample gas; a thermally insulated enclosure having the gas cell therein; a heat source or heat exchanger operable to influence an interior temperature of the thermally insulated enclosure; a light source within the thermally insulated enclosure operable to provide a mid-infrared (mid-IR) light into and through the gas cell; a photodetector within the thermally insulated enclosure operable to receive the attenuated mid-IR; and a control system electronically coupled to the vacuum system and to the pressure sensor operable to maintain the sample gas within the gas cell at the predetermined pressure to within one torr (1 Torr).
대표청구항▼
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
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. 2. A method as recited in claim 1, wherein the step (a) of 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 comprises: (a1) providing a first diode laser capable of providing a first near-IR light comprising a first frequency within a first frequency range;(a2) providing a second diode laser capable of providing a second near-IR light comprising a second frequency within a second frequency range, wherein the frequency of the second near-IR light may be tuned within the second frequency range, wherein the first and second frequency ranges are such that there exists a range of operationally achievable differences between the first and second frequencies that spans a frequency range of the rotationally resolved absorption line; and(a3) providing a non-linear crystal operable to receive the first and second near-IR lights and generate the mid-IR light. 3. A method as recited in claim 2, wherein the step (h) of 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 comprises repeatedly performing the steps of: (h1) setting a drive current supplied to the second diode laser to zero so as to extinguish emission of the mid-IR light;(h2) setting the drive current supplied to the second diode laser to a non-zero value corresponding to a starting wavelength of the mid-IR light; and(h3) varying the drive current supplied to the second diode laser such that the mid-IR wavelength continuously varies from the starting wavelength to an ending wavelength, wherein the starting wavelength and the ending wavelength span the wavelength range of the rotationally resolved absorption line. 4. A method as recited in claim 2, wherein the step (h) of 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 comprises repeatedly performing the steps of: (h1) setting a drive current supplied to the second diode laser to zero so as to extinguish emission of the mid-IR light;(h2) setting the drive current supplied to the second diode laser to a non-zero value corresponding to a starting wavelength of the mid-IR light;(h3) varying the drive current supplied to the second diode laser such that the mid-IR wavelength continuously varies from the starting wavelength to an ending wavelength, and(h4) varying the drive current supplied to the second diode laser such that the mid-IR wavelength continuously varies from the ending wavelength to the starting wavelength, wherein the starting wavelength and the ending wavelength span the wavelength range of the rotationally resolved absorption line. 5. A method as recited in claim 1, wherein the step (d) of providing temperature stabilization of the light source and the optical system includes: (d1) providing a thermoelectric element within an aperture of the thermally insulated enclosure for transferring heat either into or out of the thermally insulated enclosure;(d2) providing a first and a second heat sink and fan assembly in thermal contact with the thermoelectric element and disposed outside of and within the thermally insulated enclosure, respectively;(d3) providing a temperature sensor within the thermally insulated enclosure; and(d4) providing temperature controller circuitry in electrical communication with the temperature sensor and the thermoelectric element, the temperature controller circuitry providing a current to the thermoelectric element based on an electronic signal received from the temperature sensor. 6. A method as recited in claim 5, wherein the step (f) of providing a system for stabilizing the temperature of the sample gas flowing through the sample gas cell at a sample gas temperature comprises: (f1) providing the gas cell within the thermally insulated enclosure; and(f2) causing the temperature controller to maintain the interior of the thermally insulated enclosure at the sample gas temperature. 7. A method as recited in claim 1, wherein the step (e) of 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) comprises: (e1) providing a sample gas inlet port at a first end of the gas cell in fluid communication with the environment;(e2) providing a sample gas outlet port at a second end of the gas cell;(e3) providing a vacuum pump in fluidic communication with the sample gas outlet port and with a sample gas exhaust port;(e4) providing a pressure transducer in fluidic communication with the interior of the gas cell; and(e5) providing pressure controller circuitry in electrical communication with the pressure transducer and the vacuum pump, the pressure controller circuitry operable to cause the pumping rate of the vacuum pump to vary based on an electronic signal received from the pressure transducer. 8. A method as recited in claim 1, wherein: the step (e) of 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) comprises: (e1) providing a sample gas inlet port at a first end of the gas cell in fluid communication with the environment;(e2) providing a sample gas outlet port at the optical chamber module;(e3) providing a vacuum pump in fluidic communication with the sample gas outlet port and with a sample gas exhaust port;(e4) providing a pressure transducer in fluidic communication with the interior of the gas cell; and(e5) providing pressure controller circuitry in electrical communication with the pressure transducer and the vacuum pump, the pressure controller circuitry operable to cause the pumping rate of the vacuum pump to vary based on an electronic signal received from the pressure transducer; andthe step (g) of 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 includes causing the sample gas to continuously flush interfering gas species out of the optical chamber module. 9. A method as recited in claim 1, wherein the step (h) of 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 comprises repeatedly performing the steps of: (h1) setting an operating parameter of the light source so as to extinguish the emission of the mid-IR light from the light source;(h2) setting the operating parameter so as to cause the light source to emit light comprising a starting wavelength; and(h3) varying the operating parameter so as to cause the emitted mid-IR light wavelength to continuously vary from the starting wavelength to an ending wavelength, wherein the starting wavelength and the ending wavelength span the wavelength range of the rotationally resolved absorption line. 10. A method as recited in claim 1, wherein the step (h) of 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 comprises repeatedly performing the steps of: (h1) setting an operating parameter of the light source so as to extinguish the emission of the mid-IR light from the light source;(h2) setting the operating parameter so as to cause the light source to emit light comprising a starting wavelength;(h3) varying the operating parameter so as to cause the emitted mid-IR light wavelength to continuously vary from the starting wavelength to an ending wavelength, and(h4) varying the operating parameter so as to cause the emitted mid-IR light wavelength to continuously vary from the ending wavelength to the starting wavelength, wherein the starting wavelength and the ending wavelength span the wavelength range of the rotationally resolved absorption line. 11. A method as recited in claim 1, wherein the step (k) of constructing a direct absorption spectrum of the rotationally resolved absorption line using the plurality of data points comprises: (k1) determining a null detector response corresponding to no emission of the mid-JR light by the light source;(k2) subtracting the null detector response pointwise from the plurality of data points;(k3) fitting a model polynomial baseline using a subset of the plurality of data points outside of the wavelength range of the rotationally resolved absorption line; and(k4) subtracting, pointwise, the value of each of the plurality of data points from the value of the fitted polynomial calculated at the wavelength of each respective data point. 12. A method as recited in claim 2 wherein the step (a3) of providing a non-linear crystal comprises providing the non-linear crystal in the optical chamber module and the steps (a1) of providing the first diode laser and (a2) of providing the second diode laser comprise providing the first and second diode lasers in a separate laser chamber module.
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