High-accuracy mid-IR laser-based gas sensor

A gas sensor system for detecting and measuring the concentration of a gaseous molecular species in a sample gas comprising:

• a gas cell comprising a first gas port;
• a pressure sensor operable to sense a pressure of the sample gas within the gas cell;
• a thermally insulated enclosure having the gas cell disposed therein;
• a heat source or heat exchanger operable to influence a temperature of the interior of the thermally insulated enclosure;
• a laser module within the thermally insulated enclosure comprising:
• a first and a second laser operable to provide, respectively, a first near-infrared (near-IR) light having a first wavelength and a second near-IR light having a second wavelength;
• and
• a wavelength division multiplexer (WDM) optically coupled to the first laser and to the second laser and operable to receive the first and second near-IR lights therefrom;
• an optical fiber having a first end and a second end, the first end optically coupled to the WDM and operable to receive the first and second near-IR lights therefrom;
• an optical module within the thermally insulated enclosure that is fluidically coupled to the gas cell comprising:
• a second gas port;
• an optically non-linear crystal optically coupled to the second end of the optical fiber and operable to receive the first and second near-IR lights therefrom and to generate a mid-IR light by difference frequency generation;
• and
• an optical filter optically coupled to the non-linear crystal and operable to transmit the mid-IR light while blocking transmission of the first and second near-IR lights,
• wherein the optical filter is optically coupled to the gas cell such that, in operation, the mid-IR light is transmitted through the optical filter to the gas cell;
• a photodetector operable to receive the mid-IR light transmitted through the sample gas in the gas cell;
• a vacuum system fluidically coupled to a one of the first and second gas ports and operable to cause the sample gas to flow into the other one of the first and second gas ports and through both the gas cell and the optical module;
• and
• a control system electronically coupled to the vacuum system and to the pressure sensor, wherein the control system and the vacuum system are operable to maintain the flowing sample gas within the gas cell at a predetermined pressure.