Dr. W. Thomas Roberts Profile

Dr. W. Thomas Roberts

Member of Technical Staff at Jet Propulsion Lab

SPIE Involvement:

Author

Publications (20)

PROCEEDINGS ARTICLE | November 20, 2017

Transceiver optics for interplanetary communications

Proc. SPIE. 10565, International Conference on Space Optics — ICSO 2010

KEYWORDS: Transceivers, Telescopes, Mirrors, Sun, Scattering, Light scattering, Space telescopes, Telecommunications, Optical communications, Astronomical imaging

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PROCEEDINGS ARTICLE | November 20, 2017

Development and qualification of a fiber optic cable for Martian environments

Proc. SPIE. 10565, International Conference on Space Optics — ICSO 2010

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PROCEEDINGS ARTICLE | November 20, 2017

Multi-mode optical fibers for connecting space-based spectrometers

Proc. SPIE. 10565, International Conference on Space Optics — ICSO 2010

KEYWORDS: Optical fibers, Silica, Cladding, Spectrometers, Light scattering, Raman spectroscopy, Head, Laser induced breakdown spectroscopy, Astronomical imaging, Plasma

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Laser spectral analysis systems are increasingly being considered for in situ analysis of the atomic and molecular composition of selected rock and soil samples on other planets [1][2][3]. Both Laser Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are used to identify the constituents of soil and rock samples in situ. LIBS instruments use a high peak-power laser to ablate a minute area of the surface of a sample. The resulting plasma is observed with an optical head, which collects the emitted light for analysis by one or more spectrometers. By identifying the ion emission lines observed in the plasma, the constituent elements and their abundance can be deduced. In Raman spectroscopy, laser photons incident on the sample surface are scattered and experience a Raman shift, exchanging small amounts of energy with the molecules scattering the light. By observing the spectrum of the scattered light, it is possible to determine the molecular composition of the sample.

For both types of instruments, there are advantages to physically separating the light collecting optics from the spectroscopy optics. The light collection system will often have articulating or rotating elements to facilitate the interrogation of multiple samples with minimum expenditure of energy and motion. As such, the optical head is often placed on a boom or an appendage allowing it to be pointed in different directions or easily positioned in different locations. By contrast, the spectrometry portion of the instrument is often well-served by placing it in a more static location. The detectors often operate more consistently in a thermally-controlled environment. Placing them deep within the spacecraft structure also provides some shielding from ionizing radiation, extending the instrument’s useful life. Finally, the spectrometry portion of the instrument often contains significant mass, such that keeping it off of the moving portion of the platform, allowing that portion to be significantly smaller, less massive and less robust.

Large core multi-mode optical fibers are often used to accommodate the optical connection of the two separated portions of such instrumentation. In some cases, significant throughput efficiency improvement can be realized by judiciously orienting the strands of multi-fiber cable, close-bunching them to accommodate a tight focus of the optical system on the optical side of the connection, and splaying them out linearly along a spectrometer slit on the other end.

For such instrumentation to work effectively in identifying elements and molecules, and especially to produce accurate quantitative results, the spectral throughput of the optical fiber connection must be consistent over varying temperatures, over the range of motion of the optical head (and it’s implied optical cable stresses), and over angle-aperture invariant of the total system. While the first two of these conditions have been demonstrated[4], spectral observations of the latter present a cause for concern, and may have an impact on future design of fiber-connected LIBS and Raman spectroscopy instruments. In short, we have observed that the shape of the spectral efficiency curve of a large multi-mode core optical fiber changes as a function of input angle.

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PROCEEDINGS ARTICLE | February 24, 2017

Discovery deep space optical communications (DSOC) transceiver

Proc. SPIE. 10096, Free-Space Laser Communication and Atmospheric Propagation XXIX

KEYWORDS: Transceivers, Telescopes, Mirrors, Optical design, Beam splitters, Cameras, Space telescopes, Optical communications, Laser communications, Stray light

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PROCEEDINGS ARTICLE | March 15, 2016

Overview and status of the laser communication relay demonstration

Proc. SPIE. 9739, Free-Space Laser Communication and Atmospheric Propagation XXVIII

KEYWORDS: Telescopes, Electronics, Modulation, Satellites, Adaptive optics, Space telescopes, Telecommunications, Optical communications, Relays, Free space optics, Integrated optics, Satellite communications, Laser communications, Space operations, Data communications, Free space optical communications, Laser systems engineering

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PROCEEDINGS ARTICLE | March 15, 2016

Overview of Ground Station 1 of the NASA space communications and navigation program

Proc. SPIE. 9739, Free-Space Laser Communication and Atmospheric Propagation XXVIII

KEYWORDS: Telescopes, Adaptive optics, Clouds, Telecommunications, Optical communications, Laser safety, Laser communications, Space operations, Data communications, Laser optics, Atmospheric optics, Laser systems engineering

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PROCEEDINGS ARTICLE | March 6, 2014

Monolithic telescopes for free-space optical communications

Proc. SPIE. 8971, Free-Space Laser Communication and Atmospheric Propagation XXVI

KEYWORDS: Optical components, Reflectors, Telescopes, Mirrors, Space telescopes, Telecommunications, Optical alignment, Optical instrument design, Tolerancing, Free space optical communications

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PROCEEDINGS ARTICLE | March 6, 2014

LLCD operations using the Optical Communications Telescope Laboratory (OCTL)

Proc. SPIE. 8971, Free-Space Laser Communication and Atmospheric Propagation XXVI

KEYWORDS: Telescopes, Stars, Cameras, Sensors, Laser applications, Receivers, Clouds, Space telescopes, Laser safety, Space operations

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PROCEEDINGS ARTICLE | March 22, 2013

The Lunar Laser OCTL Terminal (LLOT) optical systems

Proc. SPIE. 8610, Free-Space Laser Communication and Atmospheric Propagation XXV

KEYWORDS: Transmitters, Telescopes, Mirrors, Beam splitters, Modulation, Sensors, Control systems, Space telescopes, Zoom lenses, Optical alignment

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PROCEEDINGS ARTICLE | March 2, 2011

Deep-space optical terminals (DOT)

Proc. SPIE. 7923, Free-Space Laser Communication Technologies XXIII

KEYWORDS: Telescopes, Modulation, Sensors, Photons, Receivers, Control systems, Space telescopes, Mars, Space operations, Signal detection

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PROCEEDINGS ARTICLE | February 26, 2010

Stray light modeling and performance of the 15cm deep space optical communications transceiver (DSOCT)

Proc. SPIE. 7587, Free-Space Laser Communication Technologies XXII

KEYWORDS: Transceivers, Telescopes, Mirrors, Sun, Scattering, Sensors, Light scattering, Space telescopes, Optical communications, Stray light

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PROCEEDINGS ARTICLE | February 26, 2010

OCTL to OICETS optical link experiment (OTOOLE) electrooptical systems

Proc. SPIE. 7587, Free-Space Laser Communication Technologies XXII

KEYWORDS: Telescopes, Mirrors, Modulation, Sensors, Satellites, Space telescopes, Telecommunications, Optical communications, Laser communications, Space operations

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PROCEEDINGS ARTICLE | February 26, 2010

Preliminary results of the OCTL to OICETS optical link experiment (OTOOLE)

Proc. SPIE. 7587, Free-Space Laser Communication Technologies XXII

KEYWORDS: Telescopes, Mirrors, Modulation, Sensors, Satellites, Receivers, Space telescopes, Optical communications, Satellite communications, Laser communications

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PROCEEDINGS ARTICLE | February 26, 2010

Data products for the OCTL to OICETS optical link experiment

Proc. SPIE. 7587, Free-Space Laser Communication Technologies XXII

KEYWORDS: Telescopes, Sensors, Satellites, Video, Receivers, Data acquisition, Optical communications, Signal detection, Binary data, Atmospheric modeling

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PROCEEDINGS ARTICLE | February 24, 2009

Canonical deep space optical communications transceiver

Proc. SPIE. 7199, Free-Space Laser Communication Technologies XXI

KEYWORDS: Transceivers, Electronics, Sensors, Control systems, Space telescopes, Optical communications, Computer aided design, Astronomical imaging, Space operations, Vibration isolation

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PROCEEDINGS ARTICLE | February 24, 2009

Compact deep-space optical communications transceiver

Proc. SPIE. 7199, Free-Space Laser Communication Technologies XXI

KEYWORDS: Transceivers, Telescopes, Mirrors, Optical design, Space telescopes, Telecommunications, Collimation, Optical communications, Optical instrument design, Optics manufacturing

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PROCEEDINGS ARTICLE | May 4, 2007

Development of laser beam transmission strategies for future ground-to-space optical communications

Proc. SPIE. 6551, Atmospheric Propagation IV

KEYWORDS: Telescopes, Mirrors, Sensors, Signal attenuation, Satellites, Laser beam propagation, Space telescopes, Optical communications, Laser safety, Space operations

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