Search

Background: The aim of this study was to investigate whether massive lumbar disc herniations (LDH) can be managed safely with non-operative treatment. Whilst most LDH are treated successfully with analgesia and physiotherapy, there is little literature regarding the treatment of massive LDH. Their impressive size raises the suspicion that they may cause cauda equina syndrome and are therefore often treated surgically. Methods: Patients were referred to our tertiary unit by either their general practitioner or the musculoskeletal service. To be included in the study, patients had to have a diagnosis of massive LDH on their initial magnetic resonance imaging (MRI) and opt for non-operative treatment. Seventeen patients with a diagnosis of massive LDH with an average follow-up of 209 days (0 to 1,005 days) were reviewed. Results: One patient was listed for surgery due to persisting radicular pain only. However, they were deemed unfit for surgery and this was therefore cancelled. One patient developed impending cauda equina syndrome and underwent urgent discectomy with no complications. All remaining patients were managed safely non-operatively with no complications. Conclusions: We conclude that the massive LDH can be safely managed non-operatively, providing patients are examined for cauda equina syndrome and are fully educated on the need to represent urgently should red-flag symptoms develop.

Rap music, once associated with low-income urban communities, has become a staple in contemporary pop culture extending globally beyond the ghettos, and projects from where it began. Along with the transcendence of the art, those who master the art are repositioning themselves in a social context. This analysis observed the content of rap lyrics to understand how the genre depicts the rappers’ regards toward and relationships with women they know intimately, particularly content that portrays these young men as “thugs.” This observation explores the characteristics put forth by the rapper, specifically those demonstrating thug characteristics, as a potential dating and mating partner for young women. This analysis takes into consideration psychological concepts offering knowledge into peoples’ perceived and real reasons for establishing relationships. Psychological theories contribute to the analysis of the observed actions and principles found in the content of the reviewed lyrics. At the core of this study are concepts of Black male masculinity and intimate relationships. This study analyzed rap lyrics to understand how the “thug” is presented to the female audience.

Who filters through information and determines what information is shared with media audiences? Who filters through information and determines what information will not be shared with media audiences? Ultimately, who controls the flow of information in the media? At times commentary pertaining to media content references media as an omnipotent individual entity selecting the content transmitted to the public, reminiscent of a Wizard of Oz manner of the all-powerful being behind the curtain. Overlooked in this perception is the reality that in mass media, there are various individuals in positions of power making decisions about the information accessed by audiences of various forms of media. These individuals are considered gatekeepers: wherein the media functions as a gate permitting some matters to be publicized and included into the public discourse while restricting other matters from making it to the public conscience. Media gatekeepers (i.e., journalists, editors) possess the power to control the gate by determining the content delivered to audiences, opening and closing the gate of information. Gatekeepers wield power over those on the other side of the gate, those seeking to be informed (audiences), as well as those seeking to inform (politics, activists, academics, etc.). The earliest intellectual explanation of gatekeeping is traced to Kurt Lewin, describing gatekeeping as a means to analyze real-world problems and observing the effects of cultural values and subjective attitudes on those problems like the distribution of food in Lewins’s seminal study, and later modified by David Manning White to examine the dissemination of information via media. In an ideal situation, the gatekeepers would be taking on the challenge of weighing the evidence of importance in social problems when selecting among the options of content and information to exhibit. Yet, decisions concerning content selection are not void of subjective viewpoints and encompass values, beliefs, and ideals of gatekeepers. The subjective attitudes of gatekeepers influence their perspective of what qualifies as newsworthy information. Hence, those in the position to determine the content transmitted through media exercise the power to shape social reality for media audiences. In the evolution of media gatekeeping theory three models have resulted from the scholarship: (1) examination of the one-way flow of information passing through a series of gates before reaching audiences, (2) the process of newsroom personnel interacting with people outside of the newsroom, and (3) the direct communication of private citizens and public officials. In traditional media and newer forms of social media, gatekeeping examination revolves around analysis of these media organizations’ news routines and narratives. Gatekeeping analysis observes human behavior and motives in order to make conceptualizations about the social world.

This paper describes an adaptive quarter wave tube used to attenuate a tone from the exhaust noise of a large diesel engine. A sliding-Goertzel algorithm was used to calculate the phase angle of the transfer function between a microphone in the adaptive quarter wave tube and in the main exhaust duct. The control system adjusted the length of the adaptive quarter wave tube until the phase angle was 90 and caused the sound pressure level at the cylinder ring frequency in the exhaust duct to be minimized. The system was able to adapt to changes in engine speed, exhaust gas temperature, and load applied to the engine. The results demonstrate that the sliding-Goertzel algorithm can be used eectively to estimate the phase angle in an adaptive

This paper reports an investigation on the influences of air−fuel injection momentum rate and the air−fuel premixing on the moderate or intense low oxygen dilution (MILD) combustion in a 20-kW recuperative furnace. Various patterns of partially and fully premixed reactants have proven experimentally to work extremely well in the present furnace. H2 recorded for a variety of equivalence ratios at a firing rate of 10 kW. The present numerical study suggests that there is a critical momentum rate of the inlet fuel−air mixture below which the MILD combustion cannot occur. Also, it is revealed, both experimentally and numerically, that, above the critical rate, both the inlet fuel−air mixedness and momentum rate impose insignificant influence on the stability of and emissions from the MILD combustion.

An online monitor has been designed, built, and tested that is capable of measuring the residual transuranic concentrations in processed high-level wastes with a detection limit of 370 Bq/ml (10 nCi/ml) in less than six hours. The monitor measures the (α,n) neutrons in the presence of gamma-ray fields up to 1 Sv/h (100 R/h). The optimum design was determined by Monte Carlo modeling and then tempered with practical engineering and cost considerations. A multiplicity counter is used in data acquisition to reject the large fraction of coincident and highly variable cosmic-ray-engendered background events and results in an S/N ratio ~1.

A field test of a complicated statically indeterminate floor system on a historic steel truss bridge has been conducted to obtain a more accurate load rating of the structure than possible using calculated predic­ tions of wheel load distributions. The empirically determined wheel load distributions resulted in the identifi­ cation of the floor system, particularly the transverse floor beams, as the element governing the load rating of the structure. Favorable lateral distribution of wheel loads among the stringers by a glued laminated treated timber deck was noted. The experimental determination of wheel load distributions has provided an inexpensive means of intelligently allocating limited county resources for the maintenance and rehabilitation of an inventory of aging bridges.

In order to determine the physical processes that govern the production of light in scintillating glasses, it is necessary to work with as-produced samples which have not been subjected to heat treatment, polishing, or other preparation. A combination of an optical system, which is insensitive to sample size and shape, and a Compton backscatter coincidence technique provides a method which gives precise and reproducible results when working with such samples.

The scintillation light output of a series of silicate glasses has been determined for a fixed electron energy deposition. The glasses are cerium-doped lithium-aluminosilicates. Scintillation light output measurements were made as a function of lithium and alumina concentration and of annealing history. In this system, the cerium outer electron cloud serves as a sensitive probe of the local glass structure. From these measurements, a sensitivity matrix relating the light output to the structure is developed and presented. A conceptual model for the behavior of the light output is also presented.

Amplitude noise spectra from the nonclassical output of an injection-locked low-temperature quantum-well laser analyzed along orthogonal polarization axes reveals correlated polarization-dependent noise. Using polarization-preserving balanced homodyne detection to suppress these effects, we demonstrate photon-number fluctuations 4.5 dB below the semiclassical shot-noise limit (within 95% of the expected squeezing based on the device efficiency). Polarization mixing through birefringent components and, more significantly, correlated fluctuations originating in the laser gain medium are shown to account for the observations.

We demonstrate the conversion of a time-varying (50-400-MHz) electrical current into an optical power with fidelity 0.8 dB (1.35 dB after correction for detection efficiency) beyond the standard quantum limit by drive-current modulation of an injection-locked quantum-well laser.

The DOE tasked PNNL to investigate possible technological avenues for substantially advancing the state-of-the-art in gamma detection via large-area plastic scintillators. This report describes progress on this project as of the conclusion of FY 2003. The primary focus of the report is on experimental tests conducted with a single large-area plastic scintillator outfitted with a variety of photomultiplier tube configurations. Measurements performed to date incude scintillator response under broad-area exposure to various point-like gamma sources, and light-output uniformity mappings obtained by varying the position of a collimated beta-source over the surface of the scintillator. Development of a Monte Carlo program for modeling the response of a large-area scintillator sensor to ionizing radiation, explicitly including resolution-broadening effects of scintillation light generation, propagation, and collection is also described.

The U.S. Department of Energy tasked Pacific Northwest National Laboratory to investigate possible technological avenues for substantially advancing the state-of-the-art in gamma detection via large-area plastic scintillators. This letter report describes progress to date on this project. Early phases of the project, which commenced in January 2003, have focused on (1) quantifying the light-collection efficiency in plastic scintillator sheets as a function of photomultiplier tube positioning and edge-area coverage, (2) developing a conceptual design for a demonstration sensor, and (3) conducting initial laboratory setup and preliminary experiments using relatively small plastic scintillators for readout technique development and benchmarking of the modeling studies.

High power InGaAs multi-mode broad area semiconductor lasers emitting between 190 nm and 980 nm are required as optical pumps for Er+ and Yb+ doped double clad fiber lasers and amplifiers. In this paper, we present performance and reliability of two generations of 100 micrometer aperture broad area devices emitting at 920 nm and 970 nm. The first generation devices have been deployed in the field with up to 2.5 W ex-facet optical power. More than 500,000 device-hrs of actual multi-cell lifetest data, and nearly 100 million accelerated device-hrs have been accumulated with 91FIT at 1.2W and 25 degrees Celsius or 1.9 million hrs MTBF at 2W and 25 degrees Celsius. A next-generation design further reduces thermal resistance, optical loss, and far-field divergence resulting in up to 4W ex-facet CW output power with superb reliability. Multi-mode fiber coupled modules demonstrate high coupling efficiency due to the reduced divergence angles of the new design. Lifetest of the new generation devices demonstrate the reliability of 167 FIT at 2W and 25 degrees Celsius or 499,000 hrs MTBF at 4W and 25 degrees Celsius.

One class of neutron spectrometers is devices that provide a measure of the neutron spectrum by using moderating and absorbing materials together with thermal-neutron detectors. Pacific Northwest National Laboratory has developed scintillating fibers that are sensitive to thermal neutrons. Because these fibers are thin, they present an enabling technology for several applications, including highly efficient neutron spectroscopy. The underlying concept is to arrange the fibers in an array of layers separated by materials whose characteristics have been chosen to optimize the instrument function for the application. Monte Carlo experiments have been performed to characterize the conceptual design and to determine the value of the concept as a tool for research and other applications.

Despite a number of noteworthy achievements in other fields, superheated droplet detectors (SDDs) and bubble chambers (BCs) have not been used for nuclear nonproliferation and arms control. This report examines these two radiation-detection technologies in detail and answers the question of how they can be or should be ''adapted'' for use in national security applications. These technologies involve closely related approaches to radiation detection in which an energetic charged particle deposits sufficient energy to initiate the process of bubble nucleation in a superheated fluid. These detectors offer complete gamma-ray insensitivity when used to detect neutrons. They also provide controllable neutron-energy thresholds and excellent position resolution. SDDs are extraordinarily simple and inexpensive. BCs offer the promise of very high efficiency ({approximately}75%). A notable drawback for both technologies is temperature sensitivity. As a result of this problem, the temperature must be controlled whenever high accuracy is required, or harsh environmental conditions are encountered. The primary findings of this work are listed and briefly summarized below: (1) SDDs are ready to function as electronics-free neutron detectors on demand for arms-control applications. The elimination of electronics at the weapon's location greatly eases the negotiability of radiation-detection technologies in general. (2) As a result of their high efficiency and sharp energy threshold, current BCs are almost ready for use in the development of a next-generation active assay system. Development of an instrument based on appropriately safe materials is warranted. (3) Both kinds of bubble detectors are ready for use whenever very high gamma-ray fields must be confronted. Spent fuel MPC and A is a good example where this need presents itself. (4) Both kinds of bubble detectors have the potential to function as low-cost replacements for conventional neutron detectors such as {sup 3}He tubes. For SDDs, this requires finding some way to get boron into the detector. For BCs, this requires finding operating conditions permitting a high duty cycle.

The ability to collect broadband spectroscopic information about chemical analytes is highly desirable. We report on a technique that combines chemically selective coatings and optical spectroscopy. A 1-meter fiber 150 micrometers in diameter has approximately 5 cm2 surface area. This entire surface is used by incorporating selective moieties into the fiber cladding. The Large-Area Chemical Sensor concept for chemical sensing and measurement is based on a combination of three techniques. Specifically, it uses: (1) optical waveguides as the sensor substrate, (2) selectively adsorbing or absorbing materials to concentrate the target materials, and (3) spectroscopic interrogation for verification and quantification. The concept has been demonstrated for an iodine sensor by co-polymerizing methyl, phenyl siloxane into di-methyl siloxane. The phenyl group forms a charge-transfer complex with iodine which has an absorption at ca. 500 nm. Fused silica is the waveguide core. This system provides sensitivities in the 10-ppm range. The concept has been implemented into a prototype field iodine sensor unit. Work on the sensor concept continues with the goal of improving the sensitivity by allowing each photon multiple opportunities to interact with a target molecule.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In a conventional FTIR, the spectral content of the light is analyzed by a Michelson interferometer or other interferometer with a moving arm. The transmitted light intensity is measured by a wavelength-insensitive detector. The interferogram derived from a Michelson interferometer lies in the temporal domain. An alternative method for obtaining the interferogram involving no moving parts is demonstrated. For this, the interferogram lies in the spatial domain. This concept has many applications to sensor systems, for instance, forming a low-cost demodulator for Bragg-grating systems or field-portable spectrometers.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Neutron-sensitive scintillating glass fiber sensors provide several advantages over 3 He and BF 3 gas-tubes for plutonium detection and surveillance. Large active areas provide significant improvements in sensitivity versus cost. In addition, the glass sensors offer a wide dynamic counting range, fast response time, and low microphonic susceptibility relative to conventional sensors. We report the results of detection limits for neutron glass panels used for portal, freight and vehicle monitoring.

A radiation detector has been assembled that monitors human intrusion in rooms containing kilogram quantities of special nuclear material (SNM). The detector is fabricated from scintillating glass fibers that contain 6 Li as the neutron absorber. The detector is designed to consume a minimum of power and to be placed in a standing position, thereby presenting a minimum profile and allowing placement in existing facilities. A small footprint is achieved by using intrinsically-thin fiber optics and by undermoderating the system. The detector operates by alarming on a rapid change in the thermal neutron count rate, which corresponds to albedo neutrons that are thermalized or absorbed in the hydrogen and carbon of human body tissues when someone enters the existing neutron flux found in SNM storage rooms.

Pacific Northwest National Laboratory is developing a fiber optic grating sensor demodulator using a low cost static Fourier-transform interferometer. The spectrometer uses a fiber optic source and a plane mirror to form an interferogram in the spatial domain that is recorded by a linear photodiode array detector. Using this instrument with an interferogram fringe spacing of 20 microns provides fiber grating strain resolution of about 700-microstrain.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High power single-mode AlGaAs semiconductor lasers operating between 820 nm and 860 nm (SDL-5400 series diodes) have been successfully qualified for deployment in many free-space inter-satellite communication link programs. Traditionally these high power devices did not have sufficient bandwidth for direct high speed modulation because of large device and package parasitics. We have improved the device parasitics of the SDL-5430 laser diode, i.e. reduced the RC product, from 240 ps to about 40 ps. The initial measurements indicate that this device (SDL-5480) is suitable for high power optical inter-satellite link (OISL) applications at data rates greater than 1 Gbit/s. The preliminary life test indicates that the new device has better a reliability than the previous design.

High power multi-mode semiconductor lasers operating between 1 Watt and 2 Watts are widely used for pumpingsolid-state lasers, active fibers and direct materials processing. In this paper, we present the high power and high temperatureperformance characteristics of 100 tm aperture broad area lasers. In addition, we will present lifetest data that supports meanlifetimes in excess of 500,000 hours for this class of lasers. 1. INTRODUCTION High power (> 1 Watt) semiconductor lasers emitting from 100 xm aperture are widely used for printing and solid-state laser pumping. The operating wavelength of these lasers is divided into two major category, based on the active layermaterial: 1) A1GaAs lasers that emitting between 790 nm and 860 nm, 2) InGaAs lasers that emitting between 900 nm and990 nm. Despite impressive reports on laser performance from InGaAsP material, there have yet been few detailed reports oflaser reliability of that material system. In this paper, we present a summary of long term high power and high temperaturestressed life tests for both A1GaAs and InGaAs material systems.The internal structure of the laser consists of an A1GaAs or InGaAs quantum well active region with AlGaAs guidingand confinement layers. The laser facet are given standard high-reflectance and low-reflectance coatings on the rear and frontfacet, respectively. In this report, the A1GaAs 100 tm broad area lasers have cavity length of 750

A neutron spectrometer is a device that measures the spectrum of the kinetic energy of neutrons. There are numerous applications that can profitably use a compact neutron spectrometer. For instance, fast neutron resonance radiography requires sufficiently high resolution (several percent) to identify the absorption spectra of carbon, nitrogen and oxygen nuclei for incident neutrons in the thermal to 5 MeV range. In the nuclear arms-control arena, a device that can collect neutron spectral information without revealing design information would have considerable value for treaty verification. Conventional neutron spectrometers operate on a time-of-flight (TOF) basis. Neutrons of interest range in energy from thermal energy (0.025 eV) to a few MeV for special nuclear material and from ca. 100 KeV to 5 MeV for identification of explosives. A thermal neutron has a speed of ca. 2,000 mis; a 1 MeV neutron has a speed of ca. 13,000 km/sec. A TOF spectrometer has a series of choppers, each turning at different speeds, that pass only those neutrons in a given energy (velocity) range; the velocity cohort that is allowed to pass through the spectrometer and be counted is selected by varying the relative speeds ofrotation. Thus, the TOF spectrometer is, by necessity, large (meters to tens of meters). In addition, only a small fraction of all the incident neutrons are measured during any given time interval. That is, the TOF spectrometer makes very inefficient use of the neutron flux. We will describe a spectrometer that has been made practical by the development of neutron-sensitive scintillating fibers. 1-s This concept is "work-in-progress" but the results of a simple theoretical test are reported here.

This paper provides a brief summary of the scintillation process in organic and inorganic materials, the properties and uses of fiber lightguides made from these materials. Also presented are some recent data on a new application of scintillating fiber lightguides in nuclear medicine.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pacific Northwest National Laboratory is developing a large- area, fiber-optic chemical sensor that combines chemically selective coatings and optical spectroscopy. This is a potentially hyphenated sensing technique because of the ability to collect broadband spectroscopic information in addition to sensing the quantity of the target species. Selective compound coating of optical waveguides enables the production of chemical sensors in large lot sizes. This paper describes the progress to date to produce iodine vapor selective fiber sensors that use through the fiber absorption spectroscopy. Spectra have been collected on uncalibrated I2/N2 gas mixtures using visible light.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We review data on the high temperature operation of a high speed data link operating at 1 micrometer wavelength. The single mode fiber packaged transmitter consists of an 'uncooled' high speed laser diode packaged with a commercial laser driver chip and operates at data rates up to 1.2 Gbit/s. The single mode fiber packaged receiver consists of a high speed photodiode packaged with a combination of a commercial transimpedance amplifier and a limiting amplifier. The link operates with high stability and very low error rates without an optical isolator. The maximum data rate and the minimum link sensitivity are currently limited by the electronic component design.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We describe advances in the development of high-power diffraction-limited lasers for single- mode fiber-coupled sources. The development of the tapered amplifier has led to the realization of a monolithic MOPA diode laser, which provides up to 3 W cw of single-spatial- mode output power. We further describe the implementation of the MOPA in fiber-coupled architectures that provide up to 1.2 W cw coupled into a single-mode optical fiber and some of the optical considerations unique to devices based on tapered amplifiers.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present data on the wide temperature operation of a high speed data link operating at nominally 1 micrometer wavelength. The single mode fiber packaged transmitter running at 1.2 GBit/s consists of a high speed laser diode packaged with a commercial laser driver chip. The laser is not cooled in any manner over the temperature range of operation and the link operates with low error rates without an optical isolator. The single mode fiber packaged receiver consists of a high speed photodiode packaged with a combination of a commercial transimpedance amplifier and a limiting amplifier.

Pacific Northwest Laboratory (PNL) has fabricated cerium-activated lithium silicate scintillating fibers via a hot-downdraw process. These fibers typically have a operational transmission length (e-1 length) of greater than 2 meters. This permits the fabrication of devices which were not possible to consider. Scintillating fibers permit conformable devices, large-area devices, and extremely small devices; in addition, as the thermal-neutron sensitive elements in a fast neutron detection system, scintillating fibers can be dispersed within moderator, improving neutron economy, over that possible with commercially available 3He or BF3 proportional counters. These fibers can be used for national-security applications, in medical applications, in the nuclear-power industry, and for personnel protection at experimental facilities. Data are presented for devices based on single fibers and devices made up of ribbons containing many fibers under high-and low-flux conditions.

Pacific Northwest Laboratory is developing a large-area chemical sensor that combines chemically selective coatings and optical spectroscopy to detect target compounds. The chemically selective material is incorporated into the cladding of an optical fiber waveguide. The material is interrogated using optical spectroscopic techniques to determine the concentration of target compounds. The optical interrogation method includes two spectroscopies: visible-near infrared absorption spectroscopy and Raman spectroscopy. This work develops the physical and mathematical models of such a sensor and provides a set of tools with which to make design predictions for the large-area chemical sensors. The theoretical relationships derived herein allow the use of bulk absorption parameters and bulk Raman coefficients to predict sensor performance.

Pacific Northwest Laboratory (PNL) has fabricated cerium-activated, lithium-silicate glass scintillating fiber neutron sensors via a hot-downdraw process. These fibers typically have a transmission length (e{sup {minus}1} length) of greater than 2 meters. The underlying physics of, the properties of, and selected devices incorporating these fibers are described. These fibers constitute an enabling technology for a wide variety of neutron sensors.

The reliability of high power continuous-wave (CW) 1 cm monolithic AlGaAs (808 nm) laser diodes is extensively investigated. Lasers with two total aperture sizes, 1800 micrometers and 3000 micrometers , are life tested at power levels of 10 W and 20 W, respectively for 1500 hours to 4000 hours at 30 degree(s)C heatsink temperature. These lasers exhibit no failures during the lifetests (total device hours of 45,000 hours for the 10 W lasers and 42,000 hours for the 20 W lasers). We demonstrate a mean time between failures (MTBF) exceeding 50,000 hours and a median life (ML) of 40,000 hours for the 10 W laser diode and a MTBF over 48,000 hours and a ML of 13,000 hours for the 20 W laser diode.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Parallel Optical Link Organization (POLO) is an industry consortium of Hewlett-Packard, Du Pont, AMP, University of Southern California, and SDL, supported by ARPA and will operate between August 1994 and August 1997. The POLO Consortium was formed to leverage the individual strengths of its members to develop low-cost, high-performance optical interconnect modules for applications in workstation clusters, high-speed switching systems, and multimedia. The goal of the program is to demonstrate the manufacturability of affordable optoelectronic transceiver modules and to provide application platforms that show a clear advantage over copper-wire interconnections. The technical objective of the program is to provide a 10 - 20 Gb/s parallel channel optical interconnect module with a projected manufacturing cost of about $10 per channel. In addition, the POLO Consortium provides a complete solution to the end user, including a programmable host interface module and software interface. The POLO Consortium has formed a User Group consisting of seven world-leading computer, telecommunication, and optoelectronic subsystem manufacturers. Regular meetings with the User Group are planned and at the first meeting, a full set of POLO Module specifications have been discussed and generated. The POLO Consortium will provide the User Group members with hardware for evaluation and feedback.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The SDL-5400 series commercial AlGaAs laser diode was characterized and screened for potential use as communication laser in the SILEX program. The lasers were initially tested through environmental extremes and for vacuum reliability to obtain preliminary indications that the laser was suitable to the requirement. Potential flight lasers were then built and screened for use. Endurance testing of samples from the potential flight lot has been completed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Long duration life tests of approximately 6,000 hours on AlGaAs single-mode lasers operating at 200 mW and 50 degree(s)C indicate that high reliability can be obtained under these conditions. The projected median life is 140,000 hr and MTBF is 100,000 hr. These results compare favorably with data from other material systems.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pacific Northwest Laboratory (PNL) has fabricated cerium-activated lithium silicate scintillating fibers via a hot-downdraw process. These fibers, which, as produced, typically have a transmission length (e−1 length) of greater than 2 meters, are found to undergo aging when subjected to room air. The aging, which is complete in a few weeks, reduces the transmission length to the order of 0.5 meter. Because of the high alkali content of the glass (on the order of 20-30 mole % lithia), we have attributed this aging to aqueous corrosion at the polymer cladding/glass interface. Changes in transmission with chemical treatment of the surface support the corrosion model. Fiber transmission performance has been preserved by modifying the hot-downdraw to a double crucible to produce glass-on-glass waveguides.

Results are presented on catastrophic damage limits and life-test measurements for four types of high-power laser diodes operating at wavelengths between 980 nm and 690 nm. The laser diodes under consideration are CW multimode lasers, CW laser bars, quasi-CW bars/2D stacked arrays, and single transverse mode lasers.

Spectral properties of commercially available Fabry-Perot and distributed Bragg reflector (DBR) GaAlAs and InGaAs laser diodes operating under deep current modulation are presented. At kHz modulation frequencies spectral widths of commercial diodes are 2.5 nm 15 dB down from the maximum intensity. Structural modifications can narrow this value to 0.4 nm. Prototype DBR devices with maximum output power of 110 mW exhibit extremely narrow CW linewidths of 4 MHz, and are suitable for coherent communication as well as direct detection communication formats.

Most neutron detection sensors presently employ 3He gas-filled detectors. Despite their excellent performance and widespread use, there are significant limitations to this technology. A significant alternative neutron sensor utilizing neutron-active material incorporated into a glass scintillator is presented that offers novel commercial sensors not possible or practical with gas tube technology. The scintillating optical fiber permits sensors with a multitude of sizes ranging from devices of a single fiber of 150µm to sensors with tens of thousands of fibers with areas as large as 5 m2 depending on the neutron flux to be measured. A second significant advantage is the use of high-speed electronics that allow a greater dynamic range, not possible with gas detectors. These sensors are flexible, conformable and less sensitive to vibration that optimizes the source-to-detector geometry and provides robust performance in field applications. The glass-fibers are sensitive to both gamma-rays and neutrons. However, the coincidence electronics are optimized for neutron to gamma-ray discrimination allowing very sensitive measurements with a low false-alarm rate. Applications include SNM surveillance, material control and accountability (MC&A), safeguard inspections, Pu health physics/bioassay and environmental characterization.

We demonstrate both common electrode and addressable arrays of single mode semiconductor lasers suitable for optical computing and optical data storage. In the common electrode geometry, eight lasers have been fabricated on a single chip which show excellent spectral and power uniformity. Total optical power obtained from this array has been in excess of 1.2 Watts CW. We have also fabricated two and nine element monolithic, individually addressable arrays with emitter spacings between 10 jim and 150 p m. Separately addressed, each element emits in a single spatial mode to greater than 0.1 Watts. For the nine element array, uniformity of better than 1.0 nanometer in wavelength and 1 milliamp in operating current across the array has been obtained. Results on crosstalk and reliability of the arrays are presented.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Existing and planned hydrologic and climatic models have important implications for water resource management in the twenty-first century and, yet, the science of validation of such models is inadequately developed to warrant full reliance on these models. Tools for such validation must be carefully crafted and broadly tested in a critical environment. Here we develop a set of validation tools and a recommended protocal for validation using graphical workstations and the programming language “S” as the key support elements. The protocol is illustrated by an example, and the recommended validation protocol is summarized in Table 1.

We investigated the effects of increasing excitation on the performance of semiconductor laser amplifiers. Amplified spontaneous emission (ASE) is a limitation to the power scaling of these devices. A Rigrod analysis is used to study the effects of ASE on the gain, signal-to-noise ratio and efficiency for different values of injection current, facet reflectivity and input laser intensity. Comparisons are made between bulk and quantum well gain media.

Optical fibers developed for sensor applications often exhibit high optical losses. While these losses may be entirely acceptable for the design application, efforts to improve fiber performance still require loss quantification and the identification of optical loss mechanisms. Existing fiber loss characterization techniques (e.g., optical time domain reflectometry) are generally only appropriate for low loss (communication grade) fibers and may give little or no information on loss mechanisms. At the Pacific Northwest Laboratory, techniques have been developed for the characterization of high-loss (tens of dB per meter) optical fibers which allow discrimination between scattering and absorptive losses. Two techniques are presented. In the "differential scattering" method, differential fiber scattering losses are acquired over the length of the fiber to obtain a scattering loss coefficient. This information combined with a conventional total fiber loss measurement (e.g., using the "cut-back" method) allows inference of the absorptive part of the fiber loss. In the second method, "scanning aperture" characteriza-tion, the fiber is scanned by a moving aperture to yield curves of differential and integral scatter intensity versus length. This curve not only provides corroboration of the previously acquired differential scattering data, but also points out high-loss regions in the optical fiber. Both methods will be fully described. Experimental data on representative fibers will be presented.

We have observed amplitude noise levels as much as 1.8 dB below the Standard quantum limit in the light generated by an external-cavity-stabilized index-guided quantum-well laser operating at room temperature. The measured amplitude noise remains more than 1.5 dB below the Standard quantum limit as the lasing wavelength of this system is tuned from 831 to 841 nm.

High-impedance pump noise suppression was used to generate amplitude squeezing in an index-guided quantum-well laser. Light exhibiting photon-number noise 1.4 dB below the shot-noise limit was observed, and the corresponding polarization properties were examined. Close-coupled laser-detector measurements made with an unsaturated detector revealed 2.9 dB of squeezing.

Geophysicists contribute their knowledge to the solution of many societal problems—seismic and volcanic risk, exploration and mapping, to name a few. A field of special demand which has recently grown important is nuclear waste disposal. To effectively contribute to this project, the geophysicist must be well versed in the underlying issues. This article summarizes the background of the nuclear waste disposal problem and how geophysicists are contributing to its solution. The emphasis is on the high‐level nuclear waste generated in the commercial sector. An accompanying article by Larry Irons illustrates some of the tools that have proved useful in hazardous waste investigations. Many of these techniques have been applied to the characterization of the site for high‐level nuclear waste. The repository program is an enormous one, perhaps the largest concentrated application of geologic knowledge ever made to a single question. There is a significant need for geophysical expertise because those techniques s...