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Publication Number
US-9989729-B2
Publication Date
2018-06-05
Expiration Date
Abstract
Systems and methods for detecting trace gases utilize a resonance optical cavity and a coherent light source coupled to the cavity through a cavity coupling mirror. The cavity is constructed of a material having the same or a similar coefficient of thermal expansion as the mirror elements defining the cavity. The main (bulk) cavity material may be the same as the main (bulk) material that forms the mirror elements, or it may be different. Such resonant cavity configurations provide improved accuracy and stability as compared to existing cavity configurations based upon similar principles.
Core Innovation
The invention relates to trace-gas detection systems using cavity-enhanced absorption spectroscopy with a resonant optical cavity. Coherent laser light is coupled into the resonant optical cavity through a cavity coupling mirror, and analytes are detected from the cavity response. The system is configured for detecting one or more analyte species present in a gaseous or liquid medium, using laser light directed into a cavity region defined between opposing mirror elements.
A key aspect of the invention is selecting the cavity body structure material and the mirror elements so that they have the same or substantially similar coefficient of thermal expansion. The cavity bulk material and mirror elements, and optional additional mirrors and mounting or optical components, are selected to reduce temperature sensitivity and mechanical stresses, thereby improving accuracy and stability. Glass and glass ceramic materials are used, including fused silica and glass-ceramics such as ULE 7972 titania-silicate glass and ZERODUR glass ceramic.
The disclosed configurations include a dual-laser single-cavity arrangement and a single-laser arrangement, with V-shaped and multi-mirror cavity geometries such as a 4-mirror configuration. Mirror optical performance is constrained using high-reflectivity mirrors with specified reflectivity thresholds, and the cavity response is related to coherent light resonance and free spectral range behavior. Embodiments further include an environmental housing with controlled pressure and temperature and temperature and pressure sensing, and a detection and processing approach to determine absorption coefficients and identify analytes including H2O, N2O, NO, NO2, CO2, CH4, and isotopes.
Claims Coverage
The independent claim focuses on a resonant optical cavity system that detects one or more analyte species in a gaseous or liquid medium using a cavity body with first and second mirror elements and two lasers coupled into the cavity through respective optical elements. Two primary inventive features are stated at the independent-claim level: thermal expansion matching between the cavity body material and the mirror materials, and directing two separate laser beams into the cavity region through the respective mirror elements.
Thermal expansion matching between cavity body and mirrors
The first mirror element and the second element define a cavity region therebetween, and the first and second mirrors are made of a material having the same or a substantially similar coefficient of thermal expansion as the first material.
Two lasers coupled into a resonant cavity via respective mirror elements
A first laser emits laser light, and at least one optical element directs the laser light of the first laser into the cavity region through the first mirror element; a second laser emits laser light, and the laser light of the second laser is directed into the cavity region through the second mirror element by the at least one optical element.
Overall, the claim coverage centers on a resonant optical cavity detector that combines same or substantially similar coefficient of thermal expansion between the cavity body structure material and the mirror materials and coupling light from two lasers into the cavity region through the first and second mirror elements.
Stated Advantages
Improves accuracy and stability by reducing temperature sensitivity and mechanical stresses.
Documented Applications
Detecting one or more analyte species present in a gaseous or liquid medium, including trace gases such as H2O, N2O, NO, NO2, CO2, CH4, and isotopes.
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