This prototype innovation is a novel design that achieves very long, effective laser path lengths that are able to yield ppb (parts per billion) and sub-ppb measurements of trace gases. SLIMS can also accommodate multiple laser channels covering a wide range of wavelengths, resulting in detection of more chemicals of interest. The mechanical design of the mirror cell allows for the large effective path length within a small footprint. The same design provides a robust structure that lends itself to being immune to some of the alignment challenges that similar cells face.
By taking a hollow cylinder and by cutting an elliptically or spherically curved surface into its inner wall, the basic geometry of a reflecting ring is created. If the curved, inner surface is diamondturned and highly polished, a surface that is very highly reflective can be formed. The surface finish can be further improved by adding a thin chrome or gold film over the surface. This creates a high-quality, curved, mirrored surface. A laser beam, which can be injected from a small bore hole in the wall of the cylinder, will be able to make many low-loss bounces around the ring, creating a large optical path length.
The reflecting ring operates on the same principle as the Herriott cell. The difference exists in the mirror that doesn’t have to be optically aligned, and which has a relatively large, internal surface area that lends itself to either open air or evacuated spectroscopic measurements. This solid, spherical ring mirror removes the possibility of mirror misalignment caused by thermal expansion or vibrations, because there is only a single, solid reflecting surface. Benefits of the reflecting ring come into play when size constraints reduce the size of the system, especially for space missions in which mass is at a premium.
This work was done by David C. Scott, Kelly Rickey, Alexander Ksendzov, Warren P. George, and Abdullah S. Aljabri of Caltech; and Joel M. Steinkraus of Cal Poly for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
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NPO-47512
This Brief includes a Technical Support Package (TSP).
Scanning Laser Infrared Molecular Spectrometer (SLIMS)
(reference NPO-47512) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package for the Scanning Laser Infrared Molecular Spectrometer (SLIMS), developed by NASA's Jet Propulsion Laboratory (JPL). It outlines the instrument's capabilities and significance in detecting trace gases in planetary atmospheres, which is crucial for understanding atmospheric evolution and the potential for life on other celestial bodies.
SLIMS employs a novel design that allows for exceptionally long effective optical path lengths within a compact structure. This design enhances the precision of gas measurements, enabling the detection of trace gases at concentrations as low as 10 parts per billion (ppb) or even sub-ppb levels. The spectrometer can operate multiple laser channels across a wide range of wavelengths, facilitating the identification of various chemicals of interest.
The document emphasizes the importance of accurately measuring trace gases to deduce the history of planetary atmospheres. By analyzing the presence and relative amounts of specific gases, scientists can infer changes in atmospheric conditions over time, including the historical presence of water and potential signs of life. The primary targets for this research include Venus and Saturn's moon, Titan, both of which have dense atmospheres that present unique scientific opportunities.
One of the challenges highlighted is the interference caused by abundant gases, such as carbon dioxide (CO2), which can obscure the detection of trace gases. To address this, the document discusses the use of CO2 filters that chemically react with CO2 to reduce its concentration in samples before analysis. However, it also notes the potential complications that could arise from such filtering processes, necessitating further testing to understand their effects on atmospheric samples.
Overall, the SLIMS project represents a significant advancement in the field of atmospheric research, combining innovative engineering with scientific inquiry to enhance our understanding of planetary atmospheres. The continued development of SLIMS will focus on optimizing its optical paths and alignment geometries to improve measurement accuracy and reliability, ultimately contributing to our knowledge of the solar system and the potential for life beyond Earth.
