A powerful tool in understanding the role that greenhouse gasses play in climate change would be real-time data from laser chemical sensors providing concentrations and locations of key gasses. The adoption and widespread use of smart mobile phones is an ideal platform on which to create an international web of data collection devices. Because long path lengths often mean more space, many precision instruments are too large to be useful anywhere outside of a lab or test bench environment. A more compact method of achieving long path lengths is needed to advance the field of trace chemical detection.
By taking a hollow cylinder and 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 diamond turned and highly polished, a surface that is very highly reflective can be formed. The surface finish can be further improved by adding a thin nickel and gold film over its surface. This surface will create a high-quality, curved mirrored surface. A laser beam, which could be injected from a small borehole in the wall of the cylinder, will be able to make many low-loss bounces around the ring and create a large optical path length.
Such cylinders could be made small enough to be integrated into an attachment for use with smart phones, and run via a smart phone application for the purpose of in situ data acquisition of the location and amounts of greenhouse gasses. Such information could be an important step towards building a web to verify and validate data that will be collected by future NASA missions whose goal will be to monitor carbon. Other key applications will include monitoring of indoor chemical pollution.
The reflecting ring operates on the same principle as the Herriott cell. The difference exists in the mirror, which does not 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. Benefits of the reflecting ring come when size constraints reduce the size of the reflecting system. The large surface area in a small package allows long path lengths to be achieved within a minimum volume. Since the ring simultaneously forms the mirror and support structure, there is no mismatch of coefficients of thermal expansion as is typically found with conventional Herriott cell configurations.
Having the optics cut from a single aluminum billet is ideal for achieving precision measurements from a mobile device. A smart phone attachment would allow for widespread use because of the already existing web of mobile device users. Through the use of advanced integrated electronics and MEMS (microelectromechanical systems) technology, it will eventually be able to miniaturize the optical, mechanical, and electronics into a compact package to fit directly into the mobile device.
A ground-based network of chemical detection devices would provide verification and validation of data from current and future NASA missions. Such a network will also enhance the tools and the information that NASA Earth scientists use to create accurate models of how Earth’s atmosphere reacts to greenhouse gasses.
This work was done by David C. Scott, Alexander Ksendzov, Warren P. George, Richard L. Baron, James A. Smith, and Abdullah S. Aljabri of Caltech; and Joel M. Steinkraus and Rudi M. Bendig of the California Polytechnic State University for NASA’s Jet Propulsion Laboratory.
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Refer to NPO-47738.