An Ultraviolet Laser for the Red Planet

Elaborate and tight cable routing: The MOMA laser without laser sheath on the exit side. (Source: LZH)

In less than three years, the rocket of the European-Russian ExoMars 2020 mission shall start its nine-month journey to Mars, together with a rover and surface platform. The flight model of the MOMA laser has reached the first milestone: the Laser Zentrum Hannover LZH has delivered the laser head to the NASA Goddard Space Flight Center, Maryland.

A major goal of the ExoMars mission is to search for past or present life on the Earth-like planet. One of the most important analytical instruments of the ExoMars rover is the German-American Mars Organic Molecule Analyzer, or MOMA for short. This is being developed together with further partners under the leadership of the Max Planck Institute for Solar System Research MPS, Göttingen, Germany. The MOMA laser model, which has been delivered to the NASA Goddard Space Flight Center, is part of the Laser Desorption Mass Spectrometer (LD-MS) developed there. On Mars, it can identify and analyze organic matter. Organic molecules in the soil samples taken in situ could provide clues to possible forms of life.

Integration of the MOMA laser into the mass spectrometer model of the NASA Goddard Space Flight Center. (Source: LZH)

In the past few years, the LZH has developed the diode-pumped solid-state laser head in the UV spectral range required for the investigations. The laser has an emission wavelength of 266 nm and an adjustable laser pulse energy of up to 130 μJ. Its most important unique features, however, are weight, size and robustness. With a length of about 20 cm it has a weight of only about 220 g. In addition, the laser head has to be pretty robust in order to function properly on Mars: Mechanical shocks during the launch of the rocket and during the landing on Mars and very large temperature differences. On the other hand, the laser optics used must withstand both the UV radiation of the laser and the ionizing cosmic radiation. The optics with space-qualified optical coatings were provided by Laseroptik GmbH and evaluated at the LZH.

“The laser is optimally adapted to the harsh environmental conditions in space and its mission on Mars,” explains Peter Wessels, Head of the Solid-State Lasers Group at the LZH. “We use a passively Q-switched Nd:YAG oscillator pumped longitudinally over an optical fiber. The infrared light of the oscillator is converted into ultraviolet radiation using nonlinear crystals. A temperature control is to ensure the function even with changing ambient temperature and also allows to flexibly adjust the output pulse energy.”

Small laser on a long journey. The laser developed by the LZH will be used in the ExoMars 2020 mission’s rover to search for life on Mars. (Source: ESA)

Before delivery of the model aircraft to NASA, the laser head was thoroughly tested at the MPS. Currently, it is being integrated into the mass spectrometer at the Goddard Space Flight Center and tested again. It then has to pass environmental tests again with NASA’s MS before being re-integrated into the Rover back in Europe. (Source: LZH)

Links: Mars Organic Molecule Analyser MOMA (F. Goesmann), Planetary Science Dept., Max-Planck-Institut für Sonnensystemforschung (MPS) Göttingen, GermanyThe ExoMars Programme 2016-2020, European Space Agency (ESA), Paris, FranceSolid-State Lasers Group (P. Weßels), Laser Development Dept., Laser Zentrum Hannover e.V. (LZH), Hanover, Germany

Further Reading: Theodor Weiss, Wolfgang Ebert (Laseroptik): Atomic Layer Deposition for Coating of Complex 3D Optics, Optik Photonik 12(3), June 2017, Pages 42–45; DOI: 10.1002/opph.201700013

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