2014 IR&D Annual Report

Development of a Compact Raman Visible Spectrograph Design for a NASA Mars 2020 Rover Instrument Proposal, 15-R8416

Principal Investigators
Greg Winters
Mike Davis
Greg Dirks
Randy Gladstone
Tommy Greathouse
Kurt Retherford
Paul Wilson

Inclusive Dates: 09/09/13 – 01/09/14

Background — In response to a NASA Mars 2020 Rover mission instrument announcement of opportunity requesting remote geological sampling instrument proposals, a Raman spectrograph concept and optical design activity commenced in the fall of 2013. Instrument proposals were due to NASA January 15, 2014. This spectrograph is a major sub-component in the remote geological sampling instrument submitted to NASA named REACH, for "Remote Raman and Laser Induced Fluorescence Emission Spectrograph for the Sample Acquisition and Habitability Assessment." Figure 1 shows the concept and overall spectrograph block diagram, including the intensified charge coupled device detector, and the super notch holographic filter.

FIGURE 1:  Optical layout of the REACH instrument, showing the Raman spectrograph.
Figure 1. Optical layout of the REACH instrument, showing the Raman spectrograph.

Approach — After spectrograph technical and performance requirements were determined, optical and mechanical design concepts were generated that provide a compact spectrograph solution for the REACH instrument proposed for the Mars 2020 Rover spaceflight and landing/survey mission. Raman spectrograph systems can be used for remote (or stand-off) sampling of geological samples. Raman spectroscopy uses monochromatic light (usually from a laser) to interact with the sample. A small portion of this incident light undergoes an inelastic, or Raman, scattering event, resulting in the wavelength of this incident light being shifted up or down after it has interacted with the sample. The shift in wavelength yields molecular and elemental information concerning the vibrational modes of the sample. The resulting spectra or "fingerprint" is then used to identify various polyatomic ions and molecules. This spectrograph design covers the 532 to 840 nm spectral range, with a resolution on the detector of 0.15nm/pixel (Nyquist samples 0.3nm), and allows measurement of Raman and fluorescence signals. Figure 2 provides the optical model of the Raman spectrograph. Figure 3 shows the mechanical package and other components.

Figure 2. Optical model, showing incoming light (on left) separated into constitute spectra (lower right) after passing through optics and the diffraction grating.
Figure 2. Optical model, showing incoming light (on left) separated into constitute spectra (lower right) after passing through optics and the diffraction grating.
Figure 3. Overall layout of the “REACH” instrument Raman spectrograph (cover removed).
Figure 3. Overall layout of the "REACH" instrument Raman spectrograph (cover removed).

Accomplishments — In response to the NASA Mars 2020 Rover mission instrument announcement of opportunity, a spectrograph design and cost proposal was submitted to the REACH instrument team. Although the REACH instrument was not selected by NASA when they announced winning teams on July 30, 2014, we were able to assist the REACH instrument team with resolving and defining spectrograph optical performance requirements and then generating a conceptual design for a high-performance Raman spectrograph that meets these requirements.

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04/15/14