Raman spectroscopy is a prime candidate for the next generation of planetary instruments, as it addresses the primary goal of mineralogical analysis, which is structure and composition. However, large fluorescence return from many mineral samples under visible light excitation can render Raman spectra unattainable. Using the described approach, Raman and fluorescence, which occur on different time scales, can be simultaneously obtained from mineral samples using a compact instrument in a planetary environment. This new approach is taken based on the use of time-resolved spectroscopy for removing the fluorescence background from Raman spectra in the laboratory.
In the SSTARS instrument, a visible excitation source (a green, pulsed laser) is used to generate Raman and fluorescence signals in a mineral sample. A spectral notch filter eliminates the directly reflected beam. A grating then disperses the signal spectrally, and a streak camera provides temporal resolution. The output of the streak camera is imaged on the CCD (charge-coupled device), and the data are read out electronically. By adjusting the sweep speed of the streak camera, anywhere from picoseconds to milliseconds, it is possible to resolve Raman spectra from numerous fluorescence spectra in the same sample. The key features of SSTARS include a compact streak tube capable of picosecond time resolution for collection of simultaneous spectral and temporal information, adaptive streak tube electronics that can rapidly change from one sweep rate to another over ranges of picoseconds to milliseconds, enabling collection of both Raman and fluorescence signatures versus time and wavelength, and Synchroscan integration that allows for a compact, low-power laser without compromising ultimate sensitivity.
This work was done by Jordana Blacksberg of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package free white paper) at www.techbriefs.com/tsp under the Physical Sciences category. NPO-46752
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Simultaneous Spectral Temporal Adaptive Raman Spectrometer — SSTARS
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Overview
The document outlines the development and capabilities of the Simultaneous Spectral Temporal Adaptive Raman Spectrometer (SSTARS), a cutting-edge instrument being developed at NASA's Jet Propulsion Laboratory (JPL). SSTARS is designed for in situ mineral analysis on planetary surfaces, utilizing advanced time-resolved spectroscopy to overcome challenges associated with fluorescence interference in Raman spectroscopy.
Raman spectroscopy is a powerful technique for identifying crystalline minerals based on their unique spectral fingerprints. However, traditional Raman instruments often struggle with high fluorescence backgrounds, which can obscure Raman signals. This issue is particularly relevant in planetary mineralogy, as demonstrated by studies on Mars meteorites, where a significant percentage of Raman spectra were undetectable due to fluorescence.
SSTARS addresses this challenge by employing a visible laser to generate both Raman and fluorescence signals while incorporating time resolution capabilities. This allows the instrument to effectively separate Raman signals from fluorescence, enabling clearer identification of minerals and trace cations. The key features of SSTARS include a compact streak tube capable of picosecond time resolution, adaptive electronics for rapid adjustments in sweep rates, and synchroscan integration for enhanced sensitivity.
The document highlights the advantages of using time-resolved spectroscopy, which takes advantage of the differing time scales of Raman scattering (occurring instantaneously) and fluorescence (which can last from picoseconds to milliseconds). By capturing both types of data simultaneously, SSTARS can provide unambiguous mineral identification and detailed information about the ions present within those minerals.
The SSTARS instrument represents a significant advancement in planetary exploration technology, offering a more effective means of analyzing mineral samples in environments where traditional methods may fail. The research and development of SSTARS are part of NASA's broader efforts to enhance our understanding of planetary materials and processes, ultimately contributing to our knowledge of planetary evolution and geology.
In summary, the SSTARS instrument is a promising tool for future planetary missions, capable of delivering high-quality mineral analysis under challenging conditions, thereby expanding our capabilities in planetary science and exploration.
