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Simulation of bent crystal spectrometers

Description: In crystal spectrometers one traditionally labels each position in the dispersion/recording plane by a single wavelength value. A simple examination of the crystal spectrometers shows that different areas of the crystal contribute different wavelengths at the same position in the recording plane. Using collimators and apertures one may reduce these effects, as well as reduce the collected signal. Convolving the system response, in that case, may not allow simple analytic estimates of the sensitivity/responsivity of the system. A Monte-Carlo ray-trace program was written in order to study and simulate the real geometry including finite source size effects. The results of using the code will be presented, demonstrating the contributions to the resolution and absolute responsivity, for a particular parabolically bent crystal spectrometer.
Date: January 1, 1984
Creator: Kyrala, G.A.
Partner: UNT Libraries Government Documents Department

Out-of-focus intensity distribution: effects of focal number and aberration

Description: Shock wave experiments contemplated on powerful CO/sub 2/ lasers require uniform planar illuminations over spot sizes much larger than the diffraction limit focal spot size of the focusing optics. Cost as well as space considerations limit one's choice of optics to parabolic mirrors with focal lengths between 78 and 150 cm, and apertures to 35 cm. Within these constraints one either modifies the incident laser energy distribution to modify the focal spot shape, or works out of the focal plane. The latter option is analyzed using a fast Fourier method to calculate the intensity distributions for two focal lengths (78 and 132 cm) and various measured optical distortions (Phase only) for the focusing optics. I found that a 78 cm element produced more uniform spots of diameter 500 ..mu..m. The 132 cm element was less sensitive to focusing/positioning error than the 78 cm element.
Date: January 1, 1981
Creator: Kyrala, G.A.
Partner: UNT Libraries Government Documents Department

Method for single-shot measurement of picosecond laser pulse-lengths without electronic time dispersion

Description: A two-source shear pattern recording is proposed as a method for single-shot measurement of the pulse shape from nearly monochromatic sources whose pulse lengths are shorter than their coherence times. The basis of this method relies on the assertion that if two identical electromagnetic pulses are recombined with a time delay greater than the sum of their pulse widths, the recordable spatial pattern has no fringes in it. At an arbitrary delay, translated into an actual spatial recording position, the recorded modulated intensity will sample the corresponding laser intensity at that delay time, but with a modulation due to the coherence function of the electromagnetic pulse. Two arrangements are proposed for recording the pattern. The principles, the design parameters, and the methodologies of these arrangements will be presented. Resolutions of the configurations and their limitations will be given as well.
Date: January 1, 1987
Creator: Kyrala, G.A.
Partner: UNT Libraries Government Documents Department

PROPX: An X-ray Manipulation Program

Description: An interactive micro-computer program that performs some manipulations on an input x-ray spectrum is introduced and described. The program is used to calculate the effect of absorption of filters, transmission through fibers, responsivity of photocathodes, responsivity of absorptive detectors, folding of responses, plotting of cross sections, and calculation, as a function of electron temperature, of the response due to a bremsstrahlung spectrum. Fluorescence from the targets is not included. Two different x-ray libraries are offered, one covers the x-ray range 30--10,000 eV with 288 energy points, and the other covers the energy range 10 eV to 1 MeV with 250 energy points per decade. 7 refs.
Date: January 1, 1992
Creator: Kyrala, G.A.
Partner: UNT Libraries Government Documents Department

Measurement of the absolute cross section for multiphoton ionization of atomic hydrogen at 248 nm

Description: We present measurements of the absolute rates for multiphoton ionization of the ground state from atomic hydrogen by a linearly polarized, subpicosecond KrF laser pulse at a wavelength of 248 nm. A laser crossed atomic beam technique is used. The irradiance was varied from 3{times}10{sup 12} w/cm{sup 2} to 2{times}10{sup 14} w/cm{sup 2} and three above threshold ionization peaks were observed. The measured rate for total electron production is less than predicted by the numerical and perturbation calculations, but significantly higher than calculated by the Reiss and Keldysh methods. 21 refs., 7 figs.
Date: January 1, 1990
Creator: Kyrala, G.A. & Nichols, T.D.
Partner: UNT Libraries Government Documents Department

Fast framing camera with independent frame adjustments

Description: We have designed, built and tested a fast framing camera that works in the visible and short infrared region of the spectrum, from 300 nm to 850 nm. The camera has four separate channels. Each framing channel has its own individual trigger input and individually adjustable framing gate width. Each channel is spatially separate from the other channels as well, thus allowing for complete independence among the four channels. The output from the four channels in the camera is recorded on one piece of 4 in. by 5 in. sheet of film. Each channel has a circular recording format with a useful diameter of 18 mm. The channels are positioned on the corners of a square with a center to center spacing of 4.45 cm (1.75 in.). The camera utilizes commercially available gated intensified microchannel-plate tubes. The camera contains its own power supply and gating circuits. It required four gating inputs (12 volts). The electronics occupy a volume of 27 cm x 33 cm x 14 cm. The framing part occupies a volume of 21 cm x 25 cm x 5 cm. Characteristics of the camera, such as: framing times, spatial modulation transfer functions, gate delay, and uniformity were studied utilizing a 35 picosecond long blue light pulse, generated by a nitrogen-pumped dye-laser system. A pulsed semiconductor laser at 820 nm was used as well for the setup.
Date: January 1, 1985
Creator: Kyrala, G.A.; McGurn, J.S.; Calligan, J. & Pallone, J.
Partner: UNT Libraries Government Documents Department

Time resolved side scatter diagnostics at NOVA

Description: Side scattering of the radiation during the interaction of a laser beam with the long scale length plasma in hohlraum is a difficult problem of relevance to the viability of ICF. It is important to measure the absolute amount of the laser side scatter as well as the angular distribution of that scatter. The OSA diagnostics has been implemented on NOVA to measure these quantities. We have implemented a fiber-optically coupled streak camera to measure the temporally and angularly resolved side scatter radiation at 351 nm at 9 different angles. Filtered PIN diodes were positioned at 31 various angles in the E-field planed and B-field plane of the incident probe beam to sample and measure the scattered radiation at the 351 nm wavelength of the probe. The diode data was used to calibrate the Brillouin power received by the 9 strategically located fiber optic channels. This presentation will describe the OSA and associated diagnostics.
Date: June 1, 1996
Creator: Kyrala, G.A.; Evans, S.C.; Jimerson, J.R. & Fernandez, J.C.
Partner: UNT Libraries Government Documents Department

MCP characterization at the Cu and Mo K{sub {alpha}} x-ray energies

Description: The authors are investigating the usefulness of microchannel plate (MCP) intensifiers for imaging x-rays at high photon energies, specifically by using filtered X-rays from an electron bombardment source to generate the K{sub {alpha}} lines of Cu at 8.04 KeV and Mo at 17.5 KeV. These high energy lines are used to measure the resolution of an MCP based intensifier produced at Los Alamos National Laboratory. They have investigated the spot size of a fielded MCP intensifier by observing, on film, the result of single photon excitation of microchannels. Measurement of the spot size was done with visible light microscopy. They report initial results of the spot size distribution in the stripline direction. They have also begun a measurement of the azimuthal anisotropy in the spatial resolution, accentuated at these energies by the inclination of the axis of the MCP channels. They concentrate on an actual ``fielded instrument`` resolution, rather than ideal, for the purpose of analyzing image data captured at the NOVA Laser Facility.
Date: March 1, 1998
Creator: Walsh, P.J.; Evans, S.; Schappert, G.T. & Kyrala, G.A.
Partner: UNT Libraries Government Documents Department

Air breakdown photography in the picosecond domain

Description: We have studied the breakdown of air using the Los Alamos Bright Source KrF laser at an irradiance of 1.36 /times/ 10/sup 16/ W/cm/sup 2/ and pulse length of 700 fs. Results of the temporal evolution of various regions of the spark, recorded with an S-20 streak/framing camera, are presented. 14 refs., 6 figs.
Date: January 1, 1989
Creator: Kyrala, G.A.; Lee, P.H.Y.; Stetler, K.A. & Yu, I.I.K.
Partner: UNT Libraries Government Documents Department

Accelerating Thick Aluminum Liners Using Pulsed Power

Description: The authors have investigated the acceleration of very thick cylindrical aluminum liners using the Pegasus II capacitory bank. These accelerated solid liners will be used to impact other objects at velocities below 1.5 km/sec, allowing one to generate and sustain shocks of a few 100 kilobar for a few microseconds. A cylindrical shell of 1100 series aluminum with an initial inner radius of 23.61 mm, an initial thickness of 3.0 mm, and a height of 20 mm, was accelerated using a current pulse of 7.15 MA peak current and a 7.4 microsecond quarter cycle time. The aluminum shell was imploded within confining copper glide planes with decreasing separation with an inward slope of 8 degrees. At impact with a cylindrical target of diameter 3-cm, the liner was moving at 1.4 km/sec and its thickness increased to 4.5 mm. Radial X-ray radiograms of the liner showed both the liner and the glide plane interface. The curvature of the inner surface of the liner was measured before impact with the 15-mm radius target. The radiograms also showed that the copper glide planes distorted as the liner radius decreased and that some axial stress is induced in the liner. The axial stresses did not affect the inner curvature significantly. Post-shot calculations of the liner behavior indicated that the thickness of the glide plane played a significant role in the distortion of the interface between the liner and the glide plane.
Date: June 28, 1999
Creator: Kyrala, G.A.; Hammerburg, J.E.; Bowers, D.; Stokes, J.; Morgan, D.V.; Anderson, W.E. et al.
Partner: UNT Libraries Government Documents Department

X rays generated in the interaction of subpicosecond laser pulses with solid targets

Description: We are investigating the generation of short pulse short wavelength x-rays for pumping inner-shell x-ray lasers by photo-ionization. In contrast with previous proposals, we are looking at the use of a single line as an efficient means of pumping these lasers. As a first step we are optimizing the flashlamp x-ray conversion efficiency and characterizing the x-ray pulse length. 18 refs., 5 figs., 2 tabs.
Date: January 1, 1991
Creator: Kyrala, G.A.; Wahlin, E.K.; Fulton, R.D.; Schappert, G.T.; Jones, L.A.; Taylor, A.J. et al.
Partner: UNT Libraries Government Documents Department

X-ray streak camera diagnostics of picosecond laser-plasma interactions

Description: An x-ray streak camera is used to diagnose a laser-produced Al plasma with time resolution of {approximately}10 ps. A streak record of filtered emission and a time-integrated transmission grating spectrum reveal that the plasma radiation is dominated by emission from He- and H-like resonance lines. 11 refs.
Date: January 1, 1992
Creator: Cobble, J.A.; Fulton, R.D.; Jones, L.A.; Kyrala, G.A.; Schappert, G.T.; Taylor, A.J. et al.
Partner: UNT Libraries Government Documents Department

Dynamic response of materials on sub-nanosecond time scales, and beryllium properties for inertial confinement fusion

Description: During the past few years, substantial progress has been made in developing experimental techniques capable of investigating the response of materials to dynamic loading on nanosecond time scales and shorter, with multiple diagnostics probing different aspects of the behavior. these relatively short time scales are scientifically interesting because plastic flow and phase changes in common materials with simple crystal structures--such as iron--may be suppressed, allowing unusual states to be induced and the dynamics of plasticity and polymorphism to be explored. Loading by laser ablation can be particularly convenient. The TRIDENT laser has been used to impart shocks and isentropic compression waves from {approx}1 to 200GPa in a range of elements and alloys, with diagnostics including surface velocimetry (line-imaging VISAR), surface displacement (framed area imaging), x-ray diffraction (single crystal and polycrystal), ellipsometry, and Raman spectroscopy. A major motivation has been the study of the properties of beryllium under conditions relevant to the fuel capsule in inertial confinement fusion: magnetically-driven shock and isentropic compression shots at Z were used to investigate the equation of state and shock melting characteristics, complemented by laser ablation experiments to investigate plasticity and heterogeneous response. These results will help to constrain acceptable tolerances on manufacturing, and possible loading paths, for inertial fusion ignition experiments at the National Ignition Facility. Laser-based techniques are being developed further for future material dynamics experiments, where it should be possible to obtain high quality data on strength and phase changes up to at least 1TPa.
Date: December 9, 2004
Creator: Swift, D C; Tierney, T E; Luo, S N; Paisley, D L; Kyrala, G A; Hauer, A et al.
Partner: UNT Libraries Government Documents Department

A Pegasus Dynamic Liner Friction Experiment

Description: The authors report on a pulsed power experiment performed at the Los Alamos National Laboratory Pegasus facility which was designed to measure material flow at metal interfaces driven to high relative velocities. Material motion at and near four flat Ta/Al(6061) interfaces was measured using flash radiographic techniques. A series of fine Pb wires (407 micron diameter) was implanted in the Al normal to the interfaces. The motion of these markers under shock loading provided a picture of material motion in the Al interfacial region. The surface roughness of the interfaces was varied between 32 and 125 micro-inches. The authors discuss the implications of these measurements for constitutive models of high speed friction and interfacial morphological change.
Date: June 28, 1999
Creator: Hammerberg, J.E.; Kyrala, G.A.; Oro, D.M.; Fulton, R.D.; Anderson, W.E.; Obst, A.W. et al.
Partner: UNT Libraries Government Documents Department

Experimental studies of x-ray emission physics and hydrodynamics using short wavelength lasers

Description: Several experimental efforts are currently under way at Low Alamos to study issues of importance for inertial confinement fusion with short wavelength lasers. These issues include the physics of x-ray conversion and the dynamics of short-wavelength laser interaction with high-Z plasmas; filamentation and self-focusing processes; and the growth of instabilities in laser-driven implosions. Most of these experiments are being pursued in collaboration with other laboratories, notably the University of Rochester and Lawrence Livermore National Laboratory. In addition, we are undertaking basic studies of the interaction of both atomic systems and solids with ultra-intense (/approximately/10/sup 17/ W/cm/sup 2/) subpicosecond lasers at Los Alamos. These experiments explore the response of atomic systems to strong fields, multiphoton excitation, and transient phenomena in dense plasmas. 15 refs., 3 figs.
Date: January 1, 1988
Creator: Goldstone, P.D.; Casperson, D.E.; Cobble, J.A.; Coggeshall, S.V.; Gomez, C.C.; Hauer, A. et al.
Partner: UNT Libraries Government Documents Department

The Los Alamos bright sources: Review of the physics and the diagnostic technology

Description: The investigation of many interesting physical phenomena in nature requires the generation of high-energy-density fields. To produce energy densities exceeding 10/sup 7/ J/cm/sup 3/ requires focusing a very powerful, very bright, short pulse laser. This talk will present a review of the physics that will be investigated with one such laser system, will describe the laser used, will describe the laser diagnostics, and will describe the physics diagnostics. The talk will emphasize the areas of research that will help the diagnostics of different aspects of these bright sources, and their interactions, especially the diagnostics of hot small volumes in picosecond time scales. 15 refs., 7 figs.
Date: January 1, 1989
Creator: Kyrala, G.A.; Schappert, G.T.; Jones, L.A.; Lee, P.H.Y.; Casperson, D.E.; Cobble, J.A. et al.
Partner: UNT Libraries Government Documents Department

Bright source lasers and experiments at very high irradiance

Description: The Los Alamos Bright Source has been assembled to explore the effects of intense coherent ultraviolet radiation on matter. This ultra-high brightness excimer laser is used to study the response of atoms, ions, and plasmas to the unique conditions the laser can provide. Primary areas of interest include properties and behavior of highly energetic atomic species, studies of possible intense field-induced nuclear transitions, pumping for x-ray lasers, and incoherent x-ray sources. The project consists of two phases: Los Alamos Bright Source I (LABS I) that is now in operation and is producing experimental data at an intensity up to 7 x 10/sup 17/ watts/cm/sup 2/ with 25 mJ of radiation and LABS II that will deliver between .1 and 1 J at an intensity of 10/sup 18/ to 10/sup 20/ w/cm/sup 2/. At these high intensities we observe collisionless excitations to the KeV level. The exact nature of the excitation process is not known and is itself part of the investigation. Because of the coherent nature of the pump and the very large fields obtainable, new regimes of optical excitation can be expected and examined. Work is underway with LABS I to produce highly ionized species and measure their spectral and other properties. This equipment has proven to be highly reliable in the last year and should afford the opportunity for many basic studies. LABS II with its increased pulse energy and intensity will support studies involving larger pump volume and higher excitation levels. It should serve as a test bed for studies of pumping schemes for x-ray lasers. 6 refs., 8 figs., 3 tabs.
Date: January 1, 1987
Creator: Jensen, R.J.; Gibson, R.B.; Schappert, G.T.; Taylor, A.J.; Roberts, J.P.; Casperson, D.E. et al.
Partner: UNT Libraries Government Documents Department

Atomic processes in plasmas under ultra-intense laser irradiation

Description: Lasers delivering subpicosecond pulses with energies of a fraction of a Joule have made it possible to generate irradiance levels approaching 10{sup 20} W/cm{sup 2}. We presently operate two such systems, a KrF based excimer laser capable of producing a few 10{sup 17} W/cm{sup 2} at 248 nm with a repetition rate of 3--5 Hz and a XeCl based excimer laser capable of producing mid 10{sup 19} W/cm{sup 2} at 308 nm and 1 Hz. We will discuss some experimental results and the theory and modeling of the interaction of such intense laser pulses with aluminum. Because of a small ASE prepulse the high intensity interaction is not at the solid surface but rather at the n{sub e} = 2 {times} 10{sup 22} cm{sup {minus}3} critical density of the blowoff plasma generated by the ASE. The transient behavior of the plasma following the energy deposition by the intense subpicosecond pulse can be viewed as the energy-impulse response of the plasma. Experimental results and modeling of the x-ray emission from this plasma will be presented. 15 refs., 8 figs.
Date: November 1, 1989
Creator: Schappert, G.T.; Casperson, D.E.; Cobble, J.A.; Comly, J.C.; Jones, L.A.; Kyrala, G.A. et al.
Partner: UNT Libraries Government Documents Department

National Ignition Campaign Hohlraum Energetics

Description: The first series of experiments on the National Ignition Facility (NIF) [E. I. Moses, R. N. Boyd, B. A. Remington, C. J. Keane, and R. Al-Ayat, 'The National Ignition Facility: ushering in a new age for high energy density science,' Phys. Plasmas 16, 041006 (2009)] tested ignition hohlraum 'energetics,' a term described by four broad goals: (1) Measurement of laser absorption by the hohlraum; (2) Measurement of the x-ray radiation flux (T{sub RAD}{sup 4}) on the surrogate ignition capsule; (3) Quantitative understanding of the laser absorption and resultant x-ray flux; and (4) Determining whether initial hohlraum performance is consistent with requirements for ignition. This paper summarizes the status of NIF hohlraum energetics experiments. The hohlraum targets and experimental design are described, as well as the results of the initial experiments. The data demonstrate low backscattered energy (< 10%) for hohlraums filled with helium gas. A discussion of our current understanding of NIF hohlraum x-ray drive follows, including an overview of the computational tools, i.e., radiation-hydrodynamics codes, that have been used to design the hohlraums. The performance of the codes is compared to x-ray drive and capsule implosion data from the first NIF experiments. These results bode well for future NIF ignition hohlraum experiments.
Date: November 16, 2009
Creator: Meezan, N B; Atherton, L J; Callahan, D A; Dewald, E L; Dixit, S N; Dzenitis, E G et al.
Partner: UNT Libraries Government Documents Department