Could life exist outside of Earth? All we know for sure is that scientists will keep exploring this question until they have a definitive answer. A compact spectroscopy instrument has been developed for use in planetary exploration. The system, called the standoff ultra-compact micro Raman (SUCR) instrument, is capable of inspection and identification of minerals, organics and biogenic materials within several centimeters (2 to 20 cm) at a 10-µm resolution. This active remote sensor system is based on a 532-nm laser and a miniature spectrometer. Researchers from NASA Langley Research Center and the University of Hawaii developed a new micro Raman spectroscopy instrument to search for life on the surface of other planets. Pictured is Derek Davis, a student from Old Dominion University, working on the instrument. Courtesy of M. Nurul Abedin, NASA Langley Research Center. Extremely compact and significantly faster than other micro-Raman instruments, the SUCR instrument uses the direct-coupled Raman system design previously developed at the University of Hawaii for remote chemical detection of samples over 100 meters away from the instrument in daylight (Spectrochim Acta A 2005). The University of Hawaii's compact instrument connects all the optics directly to the spectrometer, which significantly improves performance compared to fiber-coupled Raman systems because less signal is lost. To create the SUCR instrument, researchers at NASA Langley Research Center and the University of Hawaii modified the collection optics of the previously developed system to acquire spectra of samples closer to the instrument. The researchers also reduced the system's footprint by using a miniaturized spectrometer just 16.5 cm long, 11.4 cm wide and 12.7 cm tall. “We had to make sure the instrument was very small and light so that it could travel aboard a small, fuel-efficient spaceship that would make the nine-month journey to Mars or the six-year journey to Europa,” said M. Nurul Abedin, a researcher at NASA. “The instrument must also work with other instruments aboard a rover or lander and be unaffected by the harsh radiation conditions found on other planets.” In room-light-on conditions, researchers used SUCR to analyze minerals and organic compounds that could be associated with life on other planets, including sulfur, naphthalene, mixed samples, marble, water, calcite minerals and amino acids. By passing light from a compact pulsed laser through a cylindrical lens with a focal length of 100 mm, researchers were able to successfully measure Raman spectra from samples 10 cm away with an analysis area of 17.3 µm x 5 mm. They achieved 10-µm resolution for samples 6 centimeters away using a cylindrical lens with a 60 mm focal length. Thanks to a carefully designed optical setup, the new standoff ultra-compact micro Raman (SUCR) instrument can perform microscopic Raman analysis of samples 10 centimeters away from the instrument with 17.3-µm resolution. Courtesy of M. Nurul Abedin, NASA Langley Research Center. “We are now trying to increase the analysis area by using scanning,” said Abedin. “Because of the speed of our system, we think it will be possible to create a Raman map of an area 5 x 5 mm in only one minute. Doing this with a traditional micro-Raman system would take several days.” The research team reports that the new instrument offers several other improvements to previous micro-Raman spectroscopy instruments, which require samples to be collected prior to analysis and measurements to take place in the dark. Traditional micro-Raman instruments are also prone to interference from natural mineral fluorescence. “The limitations of current systems would significantly lower the number of samples and amount of information that could be gained from a mission to Mars, for example,” said Abedin. “We carefully designed the optics of our system to enable fast analysis under daylight conditions and to produce a strong Raman signal that isn’t as prone to interference as traditional systems.” Abedin said that the SUCR system could potentially be used for biomedical and food analyses and other applications that could benefit from fast chemical analysis without the need to send samples to a lab. As a next step, the researchers plan to test the SUCR instrument in environments that mimic those found on Mars and other planets. They will then begin the validation process to show that the device could operate accurately under conditions found in space. The research was published in Applied Optics, a publication of OSA, The Optical Society (doi: 10.1364/AO.57.000062).
