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Center Independent Research & Development: GSFC IRAD

Engineering Unit Development of the PRISMA Laser for LDMS on Mars

Completed Technology Project

Project Introduction

This effort will advance the TRL of the candidate PRISMA Mars 2020LITMS (MOMA-inspired and MatISSE-funded) laser design and leverage the MOMA-MS heritage mass spectrometer, mechanical and electronics designs.  However, a rapid in-house laser development effort is needed to support the compelling science enabled by laser desorption processing, which is compatible with a number of mass spectrometers developed by NASA GSFC (including quadrupole, time-of-flight and ion trap analyzers).  The German Aerospace Center (DLR) has refused to participate in the Mars 2020 mission, and has not committed to supplying a laser for other Discovery instrument concepts;decided not to provide the laser for the proposed PRISMA investigation, as previously anticipated, thus it is critical we push the 266 nm laser hardware progression to match or exceed the TRL of the remaining MS instrumentation.

A high-fidelity “brassboard”, or proto-flight packaged version of the Mars 2020-proposed Precision In Situ Molecular Analyzer (PRISMA) deep UV laser required for the MatISSE-funded LITMS (Linear Ion Trap Mass Spectrometer) instrument as well as at least one Discovery instrument proposal, laser will be built and tested in this effort; lessons learned from our FY14 IRAD will be incorporated into the design of the optical train implemented between the pump fiber and output window, based on our lessons learned in FY14 breadboard, and other flight laser efforts, where costs, complexity, and risks will be held to the absolute minimum.  The PRISMA LITMS laser consists of three sections:  a Q-switched oscillator, an electro-optic (EO) attenuator, and a nonlinear frequency conversion stage.  Like the MLA, LOLA, and GLAS oscillators, PRISMA LITMS will utilize Nd:YAG as the gain medium with a Cr+4:YAG passive Q-switch to achieve high peak power (~1 MW) pulsed output.  The laser is end-pumped by a fiber-coupled diode laser, which allows for a compact laser cavity (<5 cm) and remote location of the pump diode and associated control electronics to be placed virtually anywhere on the instrument deck.  The Nd:YAG laser crystal has a 2 mm undoped YAG chip, diffusion-bonded to one end to minimize pump-induced thermal distortions, enhance alignment stability, and reduce the total part count.  The oscillator stage produces 1064 nm laser pulses (>1.3 mJ) in short temporal widths (<3 ns) in bursts of up to 100 Hz.  These 1064 nm pulses are sent through a pair of specialized non-linear conversion crystals to produce a final output exceeding 250 uJ at 266 nm and ~ 1ns.  This is the radiation to be directed to the Mars soil sample for a LDMS measurement.  However, something yet to be demonstrated, (to our knowledge) is the ability to produce these pulses in a burst-mode fashion, as well as adjust the individual pulse energy, with no effect on pointing or beam quality.  We will achieve this precision 266 nm pulse, as required by the PRISMA MSLITMS science, with an EO attenuation stage ilocated after the laser oscillator and the frequency conversion section.  This EO Attenuator (EOA) consists of an RTP Pockel's cell and polarizing beam splitter (PBS) cube, which are used in concert as an active throttle for the 1064 nm pulses entering the nonlinear conversion stage.  Finally, all the components and materials are selected from the published or demonstrated list of  ≥TRL6.

The oscillator, currently in laboratory breadboard state, is operating to specifications and will be repackaged into a proto-flight engineering unit for mission performance testing and optimization.  The initial hardware enclosure design concept is complete, seen in Figure 1, and will be optimized for mass and size reduction.  Due to the extreme impact mass has on cost for any Martian rover hardware, we will focus intently on demonstrating an extremely compact design for environmental testing. 

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