Diverse electron-induced optical emissions from space observatory materials at low temperatures

Abstract

Electron irradiation experiments have investigated the diverse electron-induced optical and electrical signatures observed in ground-based tests of various space observatory materials at low temperature. Three types of light emission were observed: (i); long-duration cathodoluminescence which persisted as long as the electron beam was on (ii) short-duration (<1 s) arcing, resulting from electrostatic discharge; and (iii) intermediate-duration (~100 s) glow-termed "flares". We discuss how the electron currents and arcing-as well as light emission absolute intensity and frequency-depend on electron beam energy, power, and flux and the temperature and thickness of different bulk (polyimides, epoxy resins, and silica glasses) and composite dielectric materials (disordered SiO 2 thin films, carbon-and fiberglass-epoxy composites, and macroscopically-conductive carbon-loaded polyimides). We conclude that electron-induced optical emissions resulting from interactions between observatory materials and the space environment electron flux can, in specific circumstances, make significant contributions to the stray light background that could possibly adversely affect the performance of space-based observatories.

Properties of cathodoluminescence for cryogenic applications of SiO2-based space observatory optics and coatings

“…In addition, recent charging studies at Utah State University (USU) using low-flux intermediate-energy electron beams on thin film highly disordered SiO 2 samples exhibited not only cathodoluminescent behavior 3,11-14 but also occasional arcing under some conditions. Similar behavior was also observed in experiments for other dielectric materials including cyanate ester and epoxy resins in graphite and fiberglass composites 2,9 and Kapton HN TM polyimide and carbon-loaded polyimide nanodielectric composites 2,13 . These results suggest that materials used in structural components, optical elements, and thermal control surfaces of spacecraft and space-based observatories could, when exposed to the space plasma environment, luminesce.…”

Temporal and Spatial Correlations in Electron-Induced Arcs of Adjacent Dielectric Islands

“…ielectric materials exposed to energetic electron fluxes similar to those in space plasma environments can emit light in various forms [1]. It is important to understand these charge and discharge phenomena that occur under space-like conditions, because spacecraft charging is the leading environmental cause of spacecraft anomalies [2,3].…”

“…Continuous emission observed whenever a material is exposed to electron fluxes is termed "glow," or more properly, cathodoluminescence (CL) [4,[6][7][8]. Intermediate-duration light emissions events, which start with a large rapid spike in intensity similar to arcs and are followed by an exponential decay (~10-100 s decay constant) back to the continuous equilibrium CL intensity, have also been observed for several polymeric and composite materials [1,5].…”

Variations in Cathodoluminescent Intensity of Spacecraft Materials Exposed to Energetic Electron Bombardment

“…any highly disordered insulating materials used in spacecraft construction can exhibit electron-induced glow or cathodoluminescence when exposed to the space plasma environment [1]. Determinations of the absolute and relative cathodoluminescent intensity of spacecraft materials per incident electron flux are essential to predict and mitigate consequences for optical detection [2] and for stray light contamination in space-based observatories [1,3]. They also Research provide important information about the defect structure and electron transport properties of these materials [4][5][6][7][8].…”

“…Previous studies have focused on how the relative spectral radiance of cathodoluminescent materials varies with changes in environmental conditions, including electron energy, current density, absorbed power density, and temperature. This has led to the development of a quantitative, physicsbased model to predict the intensity of glow as a function of incident electron current density and energy, temperature, and intrinsic material properties [1,3,7,9]. However, from a practical point of view, it is also important to develop an understanding of the variations of the cathodoluminescent intensity of diverse spacecraft materials exposed to energetic electron bombardment in both the space environment and space simulation studies.…”