Curious about Mars: Rover Raman

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  • Published: Oct 1, 2017
  • Author: David Bradley
  • Channels: Raman
thumbnail image: Curious about Mars: Rover Raman

Curiouser

NASA's Curiosity rover has roamed the surface of Mars for the last five years with its ChemCam laser system capturing chemical data from its surroundings. Details of a Raman instrument that will be aboard the ChemCam on the NASA Mars 2020 rover, will be reported at the OSA Laser Congress, 1-5 October 2017 in Nagoya, Japan. (Image NASA)

NASA's Curiosity rover has roamed the surface of Mars for the last five years with its ChemCam laser system capturing chemical data from its surroundings. Details of a Raman instrument that will be aboard the ChemCam on the NASA Mars 2020 rover, will be reported at the OSA Laser Congress, 1-5 October 2017 in Nagoya, Japan.

The next Mars Rover will be launched in 2020 and will offer a new vision of the Red Planet with a faster LIBS (Laser Induced Breakdown Spectroscopy) system and an entirely new conduction-cooled laser system for non-destructive Raman spectroscopy. The latter will be capable of detecting the carbon-based signatures of organic materials.

Stacked diodes

The Thales Group is working with the Centre National d'Etudes Spatiales (CNES) and The Research Institute in Astrophysics and Planetology (IRAP), France, to develop and test the compact SuperCam system that will take Raman to Mars and be able to endure the harsh conditions there. The team will present results from a test model at the meeting. Unlike Curiosity's LIBS-only functionality, this new instrument will be able to switch between a LIBS mode and a Raman laser mode. This requires two different laser colours to excite and probe molecular vibration energies in non-destructive chemical analysis. The second colour is generated by a frequency-doubling crystal, thus precluding the need for two different lasers. This 532 nanometre beam will allow the Rover to spot organic molecules although it will not be able to discern whether the presence of such carbon compounds is due to living organisms that may or may not have existed in the planet.

The upgraded LIBS oscillator uses a diode pumped Nd:YAG crystal, as opposed to ChemCam's Nd:KGW, which provides the longer bursts but requires new methods to ensure functionality over a large temperature range. Because the Nd:YAG absorbs over a narrow range of frequencies to lase at a given temperature, the SuperCam uses a multicolour stacked diode that can pump with a wide spectrum to account for a range in temperatures.

Burst mode

"This laser is running in burst mode, but with this laser we can do 1000 shots in one burst while the ChemCam laser was 10 time less," explains Thales scientist Eric Durand. "We longitudinally pump this laser with a stack which is a broadband emitting so that when the temperature is changing, the ND:YAG crystal is still absorbing the light and the laser can be used over at least 50 to 60 degrees without temperature regulation."

To complicate matters further, the KTP crystal producing the green, frequency doubled light requires additional stabilization. "The most difficult aspect was to achieve the temperature range also with the green wavelength because we have to keep the efficiency over the whole range, and it was only possible by heating a little the KTP crystal," adds Durand.

All of this temperature stabilization must work and keep the system aligned on Mars; it is difficult enough in the laboratory, the researchers concede. Of course, it also has to survive the journey and the landing in a compact delivery capsule and so is laser welded to create strong seals. The team hopes that the capabilities of their new SuperCam will provide invaluable chemical data once the successor to Curiosity is probing the Martian surface.

Related Links

NASA 2017, online: "Mars 2020 Rover"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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