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Thunderstorm and Lightning Studies using the FORTE Optical Lightning System (FORTE/OLS)

Description: Preliminary observations of simultaneous RF and optical emissions from lightning as seen by the FORTE spacecraft are presented. RF/optical pairs of waveforms are routinely collected both as individual lightning events and as sequences of events associated with cloud-to-ground (CG) and intra-cloud (IC) flashes. CG pulses can be distinguished from IC pulses based on the properties of the RF and optical waveforms, but mostly based on the associated RF spectrograms. The RF spectrograms are very similar to previous ground-based VHF observations of lightning and show signatures associated with return strokes, stepped and dart leaders, and attachment processes,. RF emissions are observed to precede the arrival of optical emissions at the satellite by a mean value of 280 microseconds. The dual phenomenology nature of these observations are discussed in terms of their ability to contribute to a satellite-based lightning monitoring mission.
Date: February 1, 1999
Creator: Argo, P.; Franz, R.; Green, J.; Guillen, J.L.; Jacobson, A.R.; Kirkland, M. et al.
Partner: UNT Libraries Government Documents Department

Delayed Light Emission in Green Plant Meterials:Temperature-Dependence and Quantum Yield

Description: The discovery of the delayed light emission of plant materials by Strahler and Arnold in 1951 has stimulated a good deal of interest in this rather remarkable property. The emitted light has been shown to be due to an electronic transition between the first excited singlet state of chlorophyll and the ground state. At room temperature, a luminescence is observable from about 0.01 seconds to several minutes after excitation. Thus, the electronic transition cannot be rate-determining and the process represents neither normal fluorescence nor normal phosphorescence. Indeed, there is some evidence that the decay curve of the luminescence is the resultant of more than one rate-limiting process. Strahler and co-workers have been able to demonstrate the existence of many relationships between delayed light emission and photosynthesis and thus have been led to interpret the luminescence phenomena as a consequence of the reversibility of some of the enzymatic photosynthetic reactions. Moreover, Tollin and Calvin have shown that the faster decaying components of the delayed light are present to as low a temperature as -100 C, suggesting that the early processes following light-absorption are non-enzymatic in nature. These latter observations, in conjunction with several other types of experimental and theoretical information, have suggested an interpretation of the physical processes leading to delayed light emission, and, by analogy, to photosynthesis, in terms of semiconductor theory. The earlier investigations in this laboratory have been limited to the study of the light emitted approximately 0.1 seconds after excitation by a flash discharge. The recent reports of luminescences at still shorter times after excitation have prompted the construction of a device capable of continuously observing the light emission of a sample of plant material from 0.0015 seconds to about 30 seconds after the onset of flash excitation. The present work describes a series of experiments carried ...
Date: July 1, 1958
Creator: Tollin, G.; Fujimori, E. & Calvin, M.
Partner: UNT Libraries Government Documents Department

Method for removal of mercury from various gas streams

Description: The invention provides for a method for removing elemental mercury from a fluid, the method comprising irradiating the mercury with light having a wavelength of approximately 254 nm. The method is implemented in situ at various fuel combustion locations such as power plants and municipal incinerators.
Date: June 10, 2003
Creator: Granite, E. J. & Pennline, H. W.
Partner: UNT Libraries Government Documents Department

Experimental Studies of Light Emission Phenomena in Superconducting RF Cavitites

Description: Experimental studies of light emission phenomena in superconducting RF cavities, which we categorize under the general heading of cavity lights, are described. The cavity lights data, which were obtained using a small CCD video camera, were collected in a series of nine experimental runs ranging from {approx} 1/2 to {approx} 2 h in duration. The video data were recorded on a standard VHS tape. As the runs progressed, additional instrumentation was added. For the last three runs a LabVIEW controlled data acquisition system was included. These runs furnish evidence for several, possibly related, light emission phenomena. The most intriguing of these is what appear to be small luminous objects {le} 1.5 mm in size, freely moving about in the vacuum space, generally without wall contact, as verified by reflections of the tracks in the cavity walls. In addition, on a number of occasions, these objects were observed to bounce off of the cavity walls. The wall-bounce aspect of most of these events was clearly confirmed by pre-bounce and post-bounce reflections concurrent with the tracks. In one of the later runs, a mode of behavior was observed that was qualitatively different from anything observed in the earlier runs. Perhaps the most perplexing aspect of this new mode was the observation of as many as seven luminous objects arrayed in what might be described as a macromolecular formation, coherently moving about in the interior of the cavity for extended periods of time, evidently without any wall contact. It is suggested that these mobile luminous objects are without explanation within the realm of established physics. Some remarks about more exotic theoretical possibilities are made, and future plans are discussed.
Date: August 4, 2009
Creator: Anthony, P. L.; Delayen, J. R.; Fryberger, D.; Goree, W. S.; Mammosser, J.; Szalata, Z. M. et al.
Partner: UNT Libraries Government Documents Department

Fundamental role of the retarded potential in the electrodynamics of superluminal sources: reply to comment

Description: Neither Eq. (6.52) of Jackson [Classical Electrodynamics, 3rd ed. (Wiley, 1999)], or Hannay's derivation of that dquation in the preceding Comment [J. Opt. Soc. Am. A, ... (2009)], are applicable to a source whose distribution pattern moves faster than light in vacuo with nonzero acceleration. It is assumed in Hannay's derivation that the retarded distribution of the density of any moving source would be smooth and differentiable if its rest-frame distribution is. By working out an explicit example of a rotating superluminal source with a bounded and smooth density profile, we show that this assumption is erroneous. The retarded distribution of a rotating source with a moderate superluminal speed is, in general, spread over three disjoint volumes (differing in shape from each other and from the volume occupied by the source in its rest frame) whose boundaries depend on the spacetime position of the observer. Hannay overlooks the fact that the limits of integration in his expression for the retarded potential (which delineate the boundaries of the retarded distribution of the source) are not differentiable functions of the coordinates of the observer at those points on the source boundary that approach the observer, along the radiation direction, with the speed of light at the retarded time. In the superluminal regime, derivatives of the integral representing the retarded potential are well defined only as generalized functions.
Date: January 1, 2009
Creator: Singleton, John; Fasel, Joseph H; Schmidt, Andrea C; Ardavan, Houshang & Ardavan, Arzhang
Partner: UNT Libraries Government Documents Department

Electron transfer of carbonylmetalate radical pairs: femtosecond visible spectroscopy of optically excited ion pairs

Description: Charge transfer excitation at 640 nm of the cobaltocenium tetracarbonylcobaltate ion pair, [Cp{sub 2}Co{sup +}{vert_bar}Co(CO){sub 4}{sup -}], was monitored in 1,2- dichloroethane solution by femtosecond transient visible absorption spectroscopy. The absorption prepares a neutral radical pair that can undergo spontaneous back electron transfer, and which shows a double peaked spectrum with features at 760 and 815 nm at 3 ps delay time. Transient decay times of 5.8{+-}0.5 ps were measured by monitoring the decay of Co(CO){sub 4} at 757 nm and 780 nm, and these are assigned to the back electron transfer step. The ET kinetics are consistent with the previously reported rates of electron transfer that were measured for specific vibrational states by picosecond transient IR.
Date: February 1, 1997
Creator: Wen, X.; Spears, K.G.; Wiederrecht, G.P. & Wasielewski, M.R.
Partner: UNT Libraries Government Documents Department

Very High Power THz Radiation Sources

Description: We report the production of high power (20 watts average, {approx}1 Megawatt peak) broadband THz light based on coherent emission from relativistic electrons. Such sources are ideal for imaging, for high power damage studies and for studies of non-linear phenomena in this spectral range. We describe the source, presenting theoretical calculations and their experimental verification. For clarity, we compare this sources with one based on ultrafast laser techniques.
Date: October 1, 2002
Creator: Carr, G.L.; Martin, Michael C.; McKinney, Wayne R.; Jordan, Kevin; Neil, George R. & Williams, Gwyn P.
Partner: UNT Libraries Government Documents Department

Imaging white light VISAR

Description: An imaging white light velocimeter consisting of two imagine superimposing Michelson interferometers in series with the target interposed is demonstrated. Interferometrically measured 2-D velocity maps can be made of moving surfaces using unlimited bandwidth incoherent and extended area sources. Short pulse and broadband chirped pulse lasers can be used to provide temporal resolution not possible with monochromatic illumination. A 20 m/s per fringe imaging velociemter is demonstrated using an ordinary camera flash for illumination.
Date: October 1, 1996
Creator: Erskine, D.J. & Holmes, N.C.
Partner: UNT Libraries Government Documents Department

Ghost analysis visualization techniques for complex systems: examples from the NIF Final Optics Assembly

Description: The stray light or �ghost� analysis of the National Ignition Facility�s (NIP) Final Optics Assembly (FOA) has proved to be one of the most complex ghost analyses ever attempted. The NIF FOA consists of a bundle of four beam lines that: 1) provides the vacuum seal to the target chamber, 2) converts l(omega) to 3(omega) light, 3) focuses the light on the target, 4) separates a fraction of the 3(omega) beam for energy diagnostics, 5) separates the three wavelengths to diffract unwanted 1(omega) & 2(omega) light away from the target, 6) provides spatial beam smoothing, and 7) provides a debris barrier between the target chamber and the switchyard mirrors. The three wavelengths of light and seven optical elements with three diffractive optic surfaces generate three million ghosts through 4<sup>th</sup> order. Approximately 24,000 of these ghosts have peak fluence exceeding 1 J/cm<sup>2</sup>. The shear number of ghost paths requires a visualization method that allows overlapping ghosts on optics and mechanical components to be summed and then mapped to the optical and mechanical component surfaces in 3D space. This paper addresses the following aspects of the NIF Final Optics Ghost analysis: 1) materials issues for stray light mitigation, 2) limitations of current software tools (especially in modeling diffractive optics), 3) computer resource limitations affecting automated coherent raytracing, 4) folding the stray light analysis into the opto-mechanical design process, 5) analysis and visualization tools from simple hand calculations to specialized stray light analysis computer codes, and 6) attempts at visualizing these ghosts using a CAD model and another using a high end data visualization software approach.
Date: June 26, 1998
Creator: Beer, G. K.; Hendrix, J. L.; Rowe, J. & Schweyen, J.
Partner: UNT Libraries Government Documents Department

Generation of elves by sprites and jets

Description: Recent years of observations of the upper atmosphere and the lower ionosphere brought a fascinating collection of new phenomena including optical, radio, and gamma-ray emissions originating in the 20 to 90 km altitude range. Up to now, the most diverse phenomenology has emerged from the optical observations which have led to the identification of red sprites, blue jets, blue starts, and elves. Most of the studies have concentrated on relating such phenomena in the upper atmosphere to regular lightning discharges in the troposphere. The sprite/jet discharge itself can be caused by the runaway air breakdown, or regular air breakdown. The standard theory for optical airglow transients in the lower ionosphere above the thunderstorms also known as elves suggests that they are produced during interaction of electromagnetic pulses (EMP) from lightning with the lower ionosphere. Heating of the ambient electrons by the EMP in the D region can result in excitation of optical emissions once the optical excitation thresholds are reached. In this paper the authors suggest that in addition to this mechanism elves can be caused by an EMP generated by sprites and jets.
Date: April 1, 1997
Creator: Taranenko, Y.; Roussel-Dupre, R.; Yukhimuk, V. & Symbalisty, E.
Partner: UNT Libraries Government Documents Department

High power beam profile monitor with optical transition radiation

Description: A simple monitor has been built to measure the profile of the high power beam (800 kW) delivered by the CEBAF accelerator at Jefferson Lab. The monitor uses the optical part of the forward transition radiation emitted from a thin carbon foil. The small beam size to be measured, about 100 {mu}m, is challenging not only for the power density involved but also for the resolution the instrument must achieve. An important part of the beam instrumentation community believes the radiation being emitted into a cone of characteristic angle 1/{gamma} is originated from a region of transverse dimension roughly {lambda}{gamma}; thus the apparent size of the source of transition radiation would become very large for highly relativistic particles. This monitor measures 100 {mu}m beam sizes that are much smaller than the 3.2 mm {lambda}{gamma} limit; it confirms the statement of Rule and Fiorito that optical transition radiation can be used to image small beams at high energy. The present paper describes the instrument and its performance. The authors tested the foil in, up to 180 {mu}A of CW beam without causing noticeable beam loss, even at 800 MeV, the lowest CEBAF energy.
Date: June 1, 1997
Creator: Denard, J.C.; Piot, P.; Capek, K. & Feldl, E.
Partner: UNT Libraries Government Documents Department

An imaging white light velocimeter

Description: An imaging white light velocimeter consisting of 2 image superimposing Michelson interferometers in series with the target interposed is demonstrated. Interferometrically measured 2-D velocity maps can be made of moving surfaces using unlimited bandwith incoherent and extended source-area lamps. Short pulse and broadband chirped pulse lasers can be used to provide temporal resolution not previouslypossible with monochromatic illumination. A 20 m/x per fringe imaging velocimeter is demonstrated using an ordinary camera flash for illumination.
Date: October 1, 1996
Creator: Erskine, D.J. & Holmes, N.C.
Partner: UNT Libraries Government Documents Department

Multilayer coating and tests of a 10x extreme ultraviolet lithographc camera

Description: A new set of mirrors for the SANDIA I OX microstepper has been fabricated. The optics have been tested by optical profilometry, atomic force microscopy, EUV reflectometry and EUV scattering. These measurements allow one to predict the performance of the camera. Mo/Si multilayer coatings with the required thickness profile were produced by DC magnetron sputtering using shadow masks in front of the rotating substrates. The failure errors of the new mirrors (0.6 nm) are considerably smaller than those obtained previously, while mid-spatial frequency roughness still needs improvement. This roughness reduces mostly the throughput of the system; i. e. most of the scattered light occurs outside the field of the camera and there is only a small reduction of contrast or resolution.
Date: February 19, 1998
Creator: Spiller, E.; Weber, F. J.; Montcalm, C.; Baker, S. L.; Gullikson, E. M. & Underwood, J. H.
Partner: UNT Libraries Government Documents Department

Exhaust gas sensors

Description: The automotive industry needed a fast, reliable, under-the-hood method of determining nitrogen oxides in automobile exhaust. Several technologies were pursued concurrently. These sensing technologies were based on light absorption, electrochemical methods, and surface mass loading. The Y-12 plant was selected to study the methods based on light absorption. The first phase was defining the detailed technical objectives of the sensors--this was the role of the automobile companies. The second phase was to develop prototype sensors in the laboratories--the national laboratories. The final phase was testing of the prototype sensors by the automobile industries. This program was canceled a few months into what was to be a three-year effort.
Date: February 9, 1997
Creator: Hiller, J. & Miree, T.J.
Partner: UNT Libraries Government Documents Department

Visible imaging of edge turbulence in NSTX

Description: Edge plasma turbulence in tokamaks and stellarators is believed to cause the radical heat and particle flux across the separatrix and into the scrape-off-layers of these devices. This paper describes initial measurements of 2-D space-time structure of the edge density turbulence made using a visible imaging diagnostic in the National Spherical Torus Experiment (NSTX). The structure of the edge turbulence is most clearly visible using a method of gas puff imaging to locally illuminate the edge density turbulence.
Date: June 13, 2000
Creator: Zweben, S.; Maqueda, R.; Hill, K.; Johnson, D. & al, et
Partner: UNT Libraries Government Documents Department

Plane parallel radiance transport for global illumination in vegetation

Description: This paper applies plane parallel radiance transport techniques to scattering from vegetation. The leaves, stems, and branches are represented as a volume density of scattering surfaces, depending only on height and the vertical component of the surface normal. Ordinary differential equations are written for the multiply scattered radiance as a function of the height above the ground, with the sky radiance and ground reflectance as boundary conditions. They are solved using a two-pass integration scheme to unify the two-point boundary conditions, and Fourier series for the dependence on the azimuthal angle. The resulting radiance distribution is used to precompute diffuse and specular `ambient` shading tables, as a function of height and surface normal, to be used in rendering, together with a z-buffer shadow algorithm for direct solar illumination.
Date: January 5, 1997
Creator: Max, N.; Mobley, C.; Keating, B. & Wu, E.H.
Partner: UNT Libraries Government Documents Department

RULLI/a Photon Counting Imager

Description: The Remote Low Light Imaging (RULLI) system responds to individual photons using a modification to conventional image intensifier technology and fast timing electronics. Each photon received at the detector is resolved in three dimensions (X, Y, and time). The accumulation of photons over time allows the system to image with very low light levels, such as starlight illumination. Using a low power pulsed laser and very fine time discrimination, three dimensional imaging has been accomplished with a vertical resolution of five cm.
Date: October 19, 1998
Creator: Albright, K.L.; Smith, R.C.; Ho, C.; Wilson, S.K.; Bradley, J.; Bird, A. et al.
Partner: UNT Libraries Government Documents Department