W. Joe Thomes Jr

NASA · Photonics Group

The Global Ecosystems Dynamics Investigation employs three laser systems delivered by NASA Goddard Space Flight Center. We report on the status of these systems after over 2 years and 10 billion shots in orbit.

For the past 25 years, the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center's Photonics Group in the Engineering Directorate has been substantially contributing to the flight design, development, production, testing and integration of many science and navigational instruments. The Moon to Mars initiative will rely he...

The Global Ecosystem Dynamics Investigation (GEDI) instrument was designed, built, and tested in-house at NASA's Goddard Space Flight Center and launched to the International Space Station (ISS) on December 5, 2018. GEDI is a multi-beam waveform LiDAR (light detection and ranging) designed to measure the Earth's global tree height and canopy densit...

The Advanced Topographic Laser Altimeter System (ATLAS) Instrument has been in integration and testing over the past 18 months in preparation for the Ice, Cloud and Land Elevation Satellite - 2 (ICESat-2) Mission, scheduled to launch in 2017. ICESat-2 is the follow on to ICESat which launched in 2003 and operated until 2009. ATLAS will measure the...

The James Webb Space Telescope (JWST) requires testing of the full optical system in a cryogenic vacuum environment prior to launch. Challenges with the telescope architecture and the test environment led to placing removable optical test sources at the intermediate focus of this off-axis Three Mirror Anastigmat (TMA) to provide test sources in the...

With the successful field demonstration of uplink arraying at 8 GHz (X-band) at NASA's Goldstone tracking station in California and at 14 GHz (Ku-band) near the Jet Propulsion Laboratory in California, NASA is pursuing a similar demonstration of the capability at 7.1 GHz (X-band) and 30-31 GHz (Ka band) and incorporating real-time correction for at...

The Jupiter Europa Orbiter (JEO) is NASA's element of the joint Europa Jupiter System Mission (EJSM). Based on current trajectories, the spacecraft will spend a significant amount of time in the Jovian radiation belts. Therefore, research endeavors are underway to study the radiation effects on the various parts and components needed to implement t...

For the past decade NASA programs have utilized the Diamond AVIM connector for optical fiber assemblies on space flight instrumentation. These connectors have been used in communications, sensing and LIDAR systems where repeatability and high performance are required. Recently Diamond has released a smaller form factor optical fiber connector calle...

High power pulsed lasers are commonly deployed in harsh environments, like space flight and military missions, for a variety of systems such as LIDAR, optical communications over long distances, or optical firing of explosives. Fiber coupling of the laser pulse from the laser to where it is needed can often save size, reduce weight, and lead to a m...

Fibers doped with rare-earth constituents such as Er³⁺ and Yb³⁺ are exceedingly important to designers of fiber-optical systems due to their ability to amplify signals in the near infra-red, low-absorption regions of conventional silicate fibers. Extending the range of operating conditions for these systems to include adverse...

The Photonics Group at the United States NASA Goddard Space Flight Center has been supporting the design, development, manufacturing and integration of the optical fiber subsystem on the Express Logistics Carrier for the ISS. Some lessons learned are presented.

The NASA Goddard Fiber Optics Team in the Electrical Engineering Division of the Applied Engineering and Technology Directorate designed, developed and integrated the space flight optical fiber array hardware for the Lunar Reconnaissance Orbiter (LRO). The two new assemblies that were designed and manufactured at GSFC for the LRO exist in configura...

Fiber optic cables are widely used in modern systems that must provide stable operation during exposure to changing environmental conditions. For example, a fiber optic cable on a satellite may have to reliably function over a temperature range of -50°C up to 125°C. While the system requirements for a particular application will dictate the exact m...

Rare-earth-doped fibers, such as Er 3+ -and Yb 3+ -doped aluminosilicates can be advantageous in space-based systems due to their stability, their high-bandwidth transmission properties and their lightweight, small-volume properties. In such environments the effect of ionizing-radiation on the optical transmission of these fibers is of paramount im...

Over the past ten years, NASA has studied the effects of harsh environments on optical fiber assemblies for communication systems, lidar systems, and science missions. The culmination of this has resulted in recent technologies that are unique and tailored to meeting difficult requirements under challenging performance constraints. This presentatio...

Fiber optic cables are increasingly being used in harsh environments where they are subjected to vibration. Understanding the degradation in performance under these conditions is essential for integration of the fibers into the given application. System constraints often require fiber optic connectors so that subsystems can be removed or assembled...

Yb³⁺-doped silicate fibers are commonly employed in optical systems utilizing fiber lasers and amplifiers. Deployment of such materials and systems in space-based and other adverse radiation environments requires knowledge of their response to fluxes of ionizing radiation. This paper reports the results of gamma radiation exposures on a...

Gamma-radiation-induced photodarkening has been observed and characterized in a suite of Yb-doped, Er-doped and Yb/Er co-doped optical fibers. Significant reduction in the optical transmission of the fibers under passive (not pumped) conditions was observed for wavelengths across the infrared spectrum. In general, it was found that the co-doped fib...

This paper is the first in a series of publications to investigate the use of commercial-off-the-shelf (COTS) components for space flight fiber laser transmitter systems and LIDAR (laser imaging detection and ranging) detection systems. In the current study, a hermetically sealed COTS LiNbO3 optical modulator is characterized for space flight appli...

A novel multi-mode 5-fiber array assembly was developed, manufactured, characterized and then qualified for the Lunar Orbiter Laser Altimeter (LOLA). LOLA is a science data gathering instrument used for lunar topographical mapping located aboard the Lunar Reconnaissance Orbiter (LRO) mission. This LRO mission is scheduled for launch sometime in lat...

The deployment of optical fibers in adverse radiation environments, such as those encountered in a low-Earth-orbit space setting, makes critical the development of an understanding of the effect of large accumulated ionizing-radiation doses on optical components and systems. In particular, gamma radiation is known to considerably affect the perform...

Exposure of optical materials to transient-ionizing-radiation fields can give rise to transient and/or permanent photodarkening effects. In laser materials, such as YAG, such induced optical loss can result in significant degradation of the lasing characteristic of the material, making its selection for optical device applications in radiation envi...

A firing set capable of charging a 0.05 μF capacitor to 1.7 kV is constructed using a 2.5 mm diameter Series Connected Photovoltaic Array (SCPA) in lieu of a transformer as the method of high voltage generation. The source of illumination is a fiber coupled 3 W 808 nm laser diode. This paper discusses the performance and PSpice modeling of an SCPA...

Photoinduced optical absorption changes in the vacuum-ultraviolet (VUV) spectral range have been measured in poly(methylphenylsilylene) thin films under varied excitation photon energies and local atmospheric environments. Spectral changes in resonances associated with both the linear chain Si-Si backbone and the side groups of the hybrid structure...

Determination of the radiation response of doped-fiber laser materials, systems and components to relevant ionizing radiation fluxes is central to the prediction of long-term fiber-based laser performance/survivability in adverse and/or space-based environments. It is well known that optical elements that are placed into orbit around the Earth expe...

The effect of ionizing-radiation fields on optical materials is predominantly seen in changes in the transmission properties of the materials. Both transient and permanent photodarkening can occur in passive and active optical elements as a result of exposure to either short-pulsed or steady-state radiation. In laser materials, such as YAG, such in...

Electronic (UV-vis) and vibrational absorption spectroscopies were used to examine the impact of incident photon energy and local atmospheric composition on the development of photo-induced structural changes in poly[(methyl)(phenyl)silylene] thin films. The relative impact of atmosphere on the magnitude and nature of photostructural modifications...

The use of photosensitive materials for the development of integrated, refractive-index structures supporting telecom, remote sensing, and varied optical beam manipulation applications is well established. Our investigations of photosensitive phenomena in polysilanes, however, have been motivated by the desire to configure, or program, the photonic...

The application of photosensitive materials to provide immediately configurable optical device functionality in integrated photonic systems has motivated an examination of the unique materials requirements associated with this alternative operational mode. In this case, a reliable photoinduced index change is needed when photopatterning under non-l...

Polysilane materials exhibit large photo-induced refractive index changes under low incident optical fluences, making them attractive candidates for applications in which rapid patterning of photonic device structures is desired immediately prior to their use. This agile fabrication strategy for integrated photonics inherently requires that optical...

Exposure of optical materials to transient-ionizing-radiation fields can give rise to transient and/or permanent photodarkening effects. In laser materials, such as YAG, such induced optical loss can result in significant degradation of the lasing characteristic of the material, making its selection for optical device applications in radiation envi...

Exposure of optical materials to transient-ionizing-radiation fields can give rise to transient and/or permanent photodarkening effects. In laser materials, such as YAG, such induced optical loss can result in significant degradation of the lasing characteristic of the material, making its selection for optical device applications in radiation envi...

Applications requiring injection of a high-power multimode laser into multiple fibers with equal energies, or specific energy ratios, provide unique design challenges. As with most all systems, engineering trades must balance competing requirements to obtain an optimal overall design. This is particularly true when fabrication issues are considered...

Agile ready-when-needed patterning of refractive index structures in photosensitive materials requires an understanding of the impact of local application environment on mechanisms contributing to the desired photoinduced index change. The present work examines the impact of atmosphere on the photosensitive response of poly(methylphenylsilane) (PMP...

The effect of dimensionality on the photobleaching characteristics of Si-based polymers with phenyl substituents was investigated by studying the change in absorption upon exposure to 248- and 337‐nm excitation. Poly(methylphenylsilylene) was chosen as an archetype of the linear-chain polysilanes, and poly(phenylsilyne) was used as the comparable n...

of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

The first vacuum-ultraviolet spectrum of a polysilylene (chain-type polysilane) with aromatic substituents is presented. Assignments of the absorption bands of the model compound poly(methylphenylsilylene) are based on previous experimental data and theoretical electronic band structure calculations for poly(alkylsilylenes) and on ultraviolet spect...

Transient ionizing radiation fields have been observed to cause substantial optical loss in undoped LiNbO3 crystals operating at 1.06 microns. This loss is slow to recover and makes the selection of this material for Q-switch applications in radiation environments unfeasible. We have studied the effects of Mg doping on the radiation response of LiN...

Changes in the cathodoluminescent (CL) brightness and in the surface chemistry of nanoparticulate SiO 2 -coated and uncoated ZnS:Ag,Cl powder phosphor have been investigated using a PHI 545 scanning Auger electron spectrometer (AES), an Oriel optical spectrometer and a JEOL 6400 scanning electron microscope (SEM). The data were collected in a stain...

Coatings of MgO and Al2O3 were deposited on Y2O3:Eu and Y2SiO5:Tb field emission display phosphors by pulsed laser deposition. Steady-state and pulsed cathodoluminescence (CL) data were collected over a range of electron beam energies up to 4 keV. The reduced CL intensities from coated phosphors are consistent with a reduction in the energy of the...

The present work investigates the intrinsic photosensitivity of a family of poly(alkyl)(aryl)silanes and poly(hydridophenyl)silane for use in the development of photoimprinted waveguide devices. Limited testing of passive optical behavior (e.g. absorption, refractive index) and photosensitive response was performed for these materials in thin film...

Degradation of ZnS and Y2O2S cathodoluminescent (CL) phosphors has been studied at 1–4 keV using Auger electron spectroscopy simultaneous with CL. The data are consistent with an electron stimulated surface chemical reaction (ESSCR) which led to destruction of ZnS and formation of a surface nonluminescent ZnO layer as well as injection of oxygen po...

Recent advances in the phosphors used for field emission displays FEDs are discussed. After reviewing the range of voltages and phosphors being used in first generation devices, the improved properties of future generation phosphors are reviewed. Specifically, next generation displays will require better low voltage efficiencies, chromaticity, satu...

The NASA Goddard Fiber Optics Team in the Electrical Engineering Division of the Applied Engineering and Technology Directorate designed, developed and integrated the space flight optical fiber array hardware for the Lunar Reconnaissance Orbiter (LRO). The two new assemblies that were designed and manufactured at GSFC for the LRO exist in configura...

Over the past ten years, NASA has studied the effects of harsh environments on optical fiber assemblies for communication systems, lidar systems, and science missions. The culmination of this has resulted in recent technologies that are unique and tailored to meeting difficult requirements under challenging performance constraints. This presentatio...

The United States, National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC), Fiber Optics Team in the Electrical Engineering Division of the Applied Engineering and Technology Directorate, designed, developed and integrated the space flight optical fiber array hardware assemblies for the Lunar Reconnaissance Orbiter (...

Fiber optic cables are increasingly being used in harsh environments where they are subjected to vibration. Understanding the degradation in performance under these conditions is essential for integration of the fibers into the given application. System constraints often require fiber optic connectors so that subsystems can be removed or assembled...

Lasers with high peak power pulses are commonly used in spaceflight missions for a wide range of applications, from LIDAR systems to optical communications. Due to the high optical power needed, the laser has to be located on the exterior of the satellite or coupled through a series of free space optics. This presents challenges for thermal managem...

A novel multi-mode 5-fiber array assembly was developed, manufactured, characterized and then qualified for the Lunar Orbiter Laser Altimeter (LOLA). LOLA is a science data gathering instrument used for lunar topographical mapping located aboard the Lunar Reconnaissance Orbiter (LRO) mission. This LRO mission is scheduled for launch sometime in lat...