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Planetary Instrument Concepts for the Advancement of Solar System Observations

Miniature Spatial Heterodyne Time-Resolved Raman Spectrometer (SHRS) for Planetary Surface and Subsurface Boreholes Mineralogy

Completed Technology Project

Project Introduction

Objectives: The goal of this project is to develop a miniature time-resolved Raman spectrometer, of unprecedentedly small size, with high spectral resolution, a large spectral range and with high light throughput, and that can be fiber-optic coupled for surface or subsurface planetary measurements. The proposed studies are designed to develop and demonstrate a Raman spectrometer that is 5 mm or less in size, weighing only a few hundred grams, with 5 cm-1 spectral resolution and >3500 cm-1 spectral range, and that can be fiber-optic coupled to a measurement region. The spatial heterodyne Raman spectrometer (SHRS) is a radically different design for a Raman spectrometer and it offers tremendous advantages over dispersive Raman systems, including 10 to 100 times larger acceptance angle and subsequently a much larger field of view, 100 to 10,000 times higher light throughput, very high resolution in a small package, and wide spectral range. The design is amendable to miniaturization because the spectral resolution is not a strong function of device size. The proposed system has no moving parts and is compatible with pulsed laser excitation and gated detection, allowing time-resolved measurements for luminescence rejection. The spectrometer design also inherently allows 1D and 2D imaging and would allow surveying a large area around a planetary lander much faster than current instruments which can only be used for close-up measurements. The small size, weight and spectral performance of this system makes it suitable for orbiting spacecraft and planetary landers where power and space are at a premium. Expected Significance: We have already demonstrated the use of a small spatial heterodyne spectrometer that has no moving parts for Raman measurements and have shown that the spectral resolution is as good as theoretically predicted. In this proposal the SHRS will be miniaturized to the millimeter scale without sacrificing spectral performance, and a pulsed laser and gated detector will be added for time-resolved measurements to eliminate sample luminescence interference. The unprecedentedly small size and high sensitivity of the new SHRS will allow multiple spectrometers to be flown on a single spacecraft, greatly expanding the amount of information that can be gathered and increasing analysis throughput. Miniature, high performance, Raman spectrometers of the size described would be a paradigm shifting technology, where a Raman spectrometer can be thought of as a new type of in-situ chemical sensor, that provides multiple dimensions of information, including complete Raman spectral coverage without scanning, as well as spatial, temporal and chemical information. NASA Relevance: The small size of the miniature SHRS would immediately broaden the applicability of Raman for planetary spacecraft and lander applications for planetary geology, water and CO2 ice measurements, and in the broader search for inorganic and organic indicators of past or present life such as water and complex organic molecules. This new technology also has the potential to change the way air-quality monitoring is done on the International Space Station (ISS) or other habitable spacecraft for life-support gases like oxygen, nitrogen, and for potentially hazardous gases such as CO2, CO and combustible gases such as hydrogen and methane, as well as dissolved species for water quality monitoring. Key science objectives include bringing the time-resolved SHRS to between TRL 2 and TRL3, and determining limitations in terms of size and weight and limits of detection for key minerals and organic compounds, and identifying design issues related to miniaturization.

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