Larry D. Looney

Transient Radiation Effects in Low-Loss Optical Waveguides

Radiation-induced effects in low loss optical waveguides have been studied to determine parameters affecting the use of these materials in plasma diagnostic instrumentation operating in severe radiation environments. Radiation-induced luminescence of fibers was shown to result from the Cerenkov process occurring within the fibers. Both spectral data and angular dependence of luminescence were used to verify the Cerenkov effect. Absolute magnitude of luminescence data were obtained. Different fiber types were shown to exhibit comparable luminescence output. Radiation-induced absorption was measured immediately following a 40 ns radiation pulse at wavelengths of 600 nm and 800 nm. Saturation effects in absorption were observed as well as changes in fiber recovery vs time as a function of radiation dose. Step- and graded-index profile fibers were shown to exhibit comparable absorption. Fibers tested included plastic clad silica fibers, as well as graded- and step-index germanium-doped and boron-doped fibers. Plastic clad silica fibers exhibited much less radiation-induced absorption than any other fiber type. The data presented allow optical fiber data links to be designed for use in severe radiation environments where data transmission is required during, or shortly after, the radiation pulse.

Enhanced radiation resistance of high-OH silica optical fibers

High purity, high-OH, silica optical fibers were irradiated in a hydrogen atmosphere to explore hydrogen binding into defects created by the ionizing radiation. Significant improvements in subsequent measurements of steady state radiation-induced attenuation were observed. Transient and steady state radiation-induced attenuations and long term stability of the phenomena were evaluated.

Influence Of Preform Variations And Drawing Conditions On Transient Radiation Effects In Pure Silica Fibers

Radiation resistance for several fiber samples is explored, with emphasis on variations in draw temperatures for both low- and high-OH content preforms. For a given prqorm type, draw temperature had minimal effect on radiation resistance for transient conditions below 10-7s. Dosimetry techniques were inter compared for pulsed electron accelerators. A high purity, high-RH content, fiber was tested for radiation response to determine transient attenuation from 4 ns to 104s.

Transient Attenuation In Optical Fibers

Low and high energy pulsed electron beams were used to generate radiation-induced transient attenuation in high-OH, Suprasil core, PCS fibers, demonstrating the energy dependence of the radiation damage and recovery mechanisms. A radiation resistant low-OH fiber was studied and its performance contrasted to that of high-OH material. Several fibers with differing core compositions were also studied.

Influence Of Preform And Draw Conditions On Uv Transmission And Transient Radiation Sensitivity Of An Optical Fiber

UV transmission and radiation-induced attenuation were determined for fibers drawn from improved silica core/fluorosilicate clad preforms with variations in fiber coating, draw temperature, tension, and speed.

Full aperture backscatter station imager diagnostics system for far-field imaging of laser plasma instabilities on Nova

In ICF, the understanding of laser plasma scattering processes is essential for laser target coupling and for controlling the symmetry of indirect drive implosions. The existing Nova full aperture backscatter station has been useful in understanding laser plasma instabilities occurring in hohlraums by measuring the quantity, spectral distribution, and near-field spatial distributions of Brillouin and more recently Raman backscatter. Equally important is an understanding of the far-field spatial intensity distribution which could help in understanding filamentation, threshold and saturation processes. This article describes a broadband, color-corrected far-field imager and associated diagnostics capable of imaging the source of scattered light to better than 25 μm resolution. Brillouin and Raman backscatter can be imaged through the Nova beam-7 focusing lens or the imager can be used like a microscope to image side scatter from other beams.

Transient radiation effects in polarization-maintaining fibers

Polarization-maintaining fibers were irradiated with 1.5 ns electron pulses. Linearly polarized light was injected into the fiber, aligned either parallel or perpendicular to the fiber cores stress axis. Linearly polarized light was detected with a high speed optical system, with polarization axis either parallel or perpendicular to the stress axis. Light throughput and attenuation were documented in these four geometries. No differences were observed in radiation-induced attenuation between the two injection conditions when the output observations were aligned with input orientation. No evidence in this time regime was seen for radiation-induced mode crossover, i.e., no signal (to < 1% of the power transmitted along the injection axis) was observed in the cross polarization state at the output as a consequence of the irradiation.

Measurement of radiation-induced attenuation in optical fibers by optical-time-domain reflectometry

Co60 radiation-induced attenuation is measured by optical time domain reflectometry (OTDR) techniques and compared to conventional optical throughput measurements. Relative advantages and disadvantages of the OTDR technique are discussed.

Optical Characterization Of Radiation-Resistant Fibers

Various measurements have been made on step index fibers having pure silica cores which are expected to have good radiation hardness properties. These measurements include spec-tral attenuation, numerical aperture, and bandwidth. Values for the preceeding quantities are given for several step index fibers of various diameters including the following: plastic-clad silica (PCS), QSF-AS, Raychem VSC, Dainichi Diaguide, and Ensign-Bickford fiber. Computer-controlled instrumentation was developed for these measurements and is described.

Radiation Damage In Optical Fibers

Optical fibers provide important advantages over coaxial cables for many data trans-mission applications. Some of these applications require that the fibers transmit data during a radiation pulse. Other applications utilize the fiber as a radition-to-light transducer. In either case, radiation-induced luminescence and absorption must be under-stood.