265 Matching Results

Search Results

Advanced search parameters have been applied.

Near field imaging of a saturated table top x-ray laser

Description: High resolution 2D imaging experiment on the saturated 18.9 nm Ni-like soft X-ray laser is presented. The imaging experiment allows measurement of the absolute output energy and intensity of the X-ray laser, while it gives detailed information on the spatial characteristics of the X-ray laser for understanding the physics and further improving the performance of the X-ray laser.
Date: June 25, 1999
Creator: Dunn, J; Li, Y; Nilsen, J; Osterheld, A & Shlyaptsev, V N
Partner: UNT Libraries Government Documents Department

Spatial coherence measurements of a 13.2 nm transient nickel-likecadmium soft x-ray laser pumped at grazing incidence

Description: We report the experimental confirmation of the production of element 110. In the bombardment of a {sup 208}Pb target with a 309 MeV {sup 64}Ni beam, we have observed two chains of time- and position-correlated events. Each chain consisted of the implantation of an evaporation residue followed by the emission of {alpha}-particles. We attribute these two chains to the decay of {sup 271}110 produced with a cross section of 8.3{sup +11}{sub -5.3} pb.
Date: September 27, 2006
Creator: Lui, Y.; Wang, Y.; Larotonda, M.A.; Luther, B.M.; Rocca, J.J. & Attwood, D.T.
Partner: UNT Libraries Government Documents Department

Application of soft x-ray laser interferometry to study large-scale-length, high-density plasmas

Description: We have employed a Mach-Zehnder interferometer, using a Ne-like Y x- ray laser at 155 {Angstrom} as the probe source, to study large-scale- length, high-density colliding plasmas and exploding foils. The measured density profile of counter-streaming high-density colliding plasmas falls in between the calculated profiles using collisionless and fluid approximations with the radiation hydrodynamic code LASNEX. We have also performed simultaneous measured the local gain and electron density of Y x-ray laser amplifier. Measured gains in the amplifier were found to be between 10 and 20 cm{sup {minus}1}, similar to predictions and indicating that refraction is the major cause of signal loss in long line focus lasers. Images showed that high gain was produced in spots with dimensions of {approximately} 10 {mu}m, which we believe is caused by intensity variations in the optical drive laser. Measured density variations were smooth on the 10-{mu}m scale so that temperature variations were likely the cause of the localized gain regions. We are now using the interferometry technique as a mechanism to validate and benchmark our numerical codes used for the design and analysis of high-energy-density physics experiments. 11 refs., 6 figs.
Date: May 1, 1996
Creator: Wan, A.S.; Barbee, T.W., Jr. & Cauble, R.
Partner: UNT Libraries Government Documents Department

Application of a high-density gas laser target to the physics of x-ray lasers and coronal plasmas

Description: An experiment has been proposed to investigate a photopumped x-ray laser approach using a novel, high-density, laser heated supersonic gas jet plasma to prepare the lasant plasma. The scheme uses the He- like sodium 1.10027 nm line to pump the He-like neon 1s-4p transition at 1.10003 nm with the lasing transitions between the n=4 to n=2,3 states and the n=3 to n=2 state at 5.8 nm, 23.0 nm, and 8.2 nm, respectively. The experiment had been proposed in 1990 and funding began Jan. 1991; however circumstances made it impossible to pursue the research over the past 5 years, and it was decided not to pursue the research any further.
Date: May 31, 1996
Creator: Pronko, J.G. & Kohler, D.
Partner: UNT Libraries Government Documents Department

Traveling wave pumping of ultra-short pulse x-ray lasers

Description: Pumping of proposed inner-shell photo-ionized (ISPI) x-ray lasers places stringent requirements on the optical pump source. We investigate these requirements for an example x-ray laser (XRL) in Carbon lasing on the 2p-1s transition at 45 A. Competing with this lasing transition is the very fast Auger decay rate out of the upper lasing state, such that the x-ray laser would self-terminate on a femto- second time scale. XRL gain may be demonstrated if pump energy is delivered in a time short when compared to the Auger rate. The fast self-termination also demands that we sequentially pump the length of the x-ray laser at the group velocity of the x-ray laser. This is the classical traveling wave requirement. It imposes a condition on the pumping source that the phase angle of the pump laser be precisely de- coupled from the pulse front angle. At high light intensities, this must be performed with a vacuum grating delay line. We will also include a discussion of issues related to pump energy delivery, i.e. pulse-front curvature, temporal blurring and puke fidelity. An all- reflective optical system with low aberration is investigated to see if it fulfills the requirements. It is expected that these designs together with new high energy (>1J) ultra-short pulse (< 40 fs) pump lasers now under construction may fulfill our pump energy conditions and produce a tabletop x-ray laser.
Date: November 10, 1997
Creator: Snavely, R.A.; Da Silva, L.B.; Eder, D.C.; Matthews, D.L. & Moon, S.J.
Partner: UNT Libraries Government Documents Department

Thomson scattering from inertial confinement fusion plasmas

Description: Thomson scattering has been developed at the Nova laser facility as a direct and accurate diagnostic to characterize inertial confinement fusion plasmas. Flat disks coated with thin multilayers of gold and beryllium were with one laser beam to produce a two ion species plasma with a controlled amount of both species. Thomson scattering spectra from these plasmas showed two ion acoustic waves belonging to gold and beryllium. The phase velocities of the ion acoustic waves are shown to be a sensitive function of the relative concentrations of the two ion species and are in good agreement with theoretical calculations. These open geometry experiments further show that an accurate measurement of the ion temperature can be derived from the relative damping of the two ion acoustic waves. Subsequent Thomson scattering measurements from methane-filled, ignition-relevant hohlraums apply the theory for two ion species plasmas to obtain the electron and ion temperatures with high accuracy. The experimental data provide a benchmark for two-dimensional hydrodynamic simulations using LASNEX, which is presently in use to predict the performance of future megajoule laser driven hohlraums of the National Ignition Facility (NIF). The data are consistent with modeling using significantly inhibited heat transport at the peak of the drive. Applied to NIF targets, this flux limitation has little effect on x- ray production. The spatial distribution of x-rays is slightly modified but optimal symmetry can be re-established by small changes in power balance or pointing. Furthermore, we find that stagnating plasma regions on the hohlraum axis are well described by the calculations. This result implies that stagnation in gas-filled hohlraums occurs too late to directly affect the capsule implosion in ignition experiments.
Date: July 8, 1997
Creator: Glenzer, S.H.; Back, C.A. & Suter, L.J.
Partner: UNT Libraries Government Documents Department

Table-top transient collisional excitation x-ray laser research at LLNL

Description: We describe recent experiments at the Lawrence Livermore National Laboratory (LLNL) to produce a table-top x-ray laser. Using a combination of long 800 ps and short {approximately}1 ps high power laser pulses with {approximately} 6 J in each beam, a transient collisionally excited Ne-like ion x-ray laser scheme has been investigated. We present results of high x-ray laser gain for the Ne- like Ti 3p-3s J=O-l transition at 326 {Angstrom} and have achieved gL product of 15 for target lengths up to 1 cm. We have extended the transient collisional scheme to shorter wavelengths using the Ni-like analog, specifically the 4d-4p J=O-l of Ni-like Pd at 147 {Angstrom}.
Date: October 6, 1997
Creator: Dunn, J.; Osterheld, A. L.; Shepherd, R.; White, W. E.; Shlyaptsev, V. N.; Bullock, A. B. et al.
Partner: UNT Libraries Government Documents Department

Modleing of psec laser driven Ne-like and Ni-like x-ray lasers

Description: This paper models recent experiments in which a solid titanium target was illuminated by several joules of combined energy from a nsec laser pulse to create a preplasma followed by a psec laser pulse to drive the gain. Gains greater than 200 cm{sup -1} are predicted for the Ne-like Ti 3p {sup 1}S{sub 0} {yields} 3s {sup 1}P{sub 1} transition at 32.6 nm which is driven by the monopole collisional excitation. High gain is also predicted for the 3d {sup 1}P{sub 1} {yields} 3p {sup 1}P{sub 1} transition at 30.1 nm which is driven by a combination of collisional excitation and self photopumping. We also discuss the possibilities for driving a Ne-like Ge laser using this approach. For the Ni-like ions we model a solid molybdenum target under similar conditions used for Ti and predict gains greater than 300 cm{sup -1} for the Ni-like Mo 4d {sup 1}S{sub 0} {yields} 4p {sup 1}P{sub 1} transition at 18.9 nm which is driven by the monopole collisional excitation. High gain is also predicted for a self photopumped 4f {sup 1}P{sub 1} {yields} 4d {sup 1}P{sub 1} transition at 22.0 nm and several other transitions driven by inner shell collisional ionization.
Date: June 1, 1997
Creator: Nilsen, J.
Partner: UNT Libraries Government Documents Department

Reflection Imaging X-Ray Laser Microscope (RIXRALM) and its biological applications. Progress report

Description: The main stimulus for the development of the proposed microscope (RIXRALM) is the possibility to view the surface and near surface structure of biological materials, such as cell membranes at much higher resolution than an optical (confocal) microscope. Although the prediction resolution of RIXRALM was lower than a Scanning Electron Microscope (SEM), the possibility to obtain images of cells (membranes) in a more natural, hydrated state and, in many cases, without staining, made the idea of a reflection X-ray microscope very attractive. The specimen can be in an H{sub 2}O saturated He atmosphere at atmospheric pressure. As the image can be obtained quickly (nsec exposure, occurring within seconds of insertion into such an environment), the cell surface can be seen in a state which is very close to its natural condition. Besides, the short exposure time eliminates the effect of motional blurring on the images. Their X-ray reflection microscope fit well in the very large gap in the size of biological objects studied in light microscopy (sub-micron size) and electron microscope (down to a few nanometers size).
Date: July 1, 1998
Creator: Suckewer, S.
Partner: UNT Libraries Government Documents Department

Simulation of the fundamental and nonlinear harmonic output from an FEL amplifier with a soft x-ray seed laser

Description: A single-pass, high-gain free-electron laser (FEL) x-ray amplifier was simulated using the 3D, polychromatic simulation code MEDUSA. The seed for the system is a table-top, soft x-ray laser. The simulated fundamental and nonlinear harmonic x-ray output wavelengths are discussed.
Date: July 5, 2000
Creator: Biedron, S. G.; Freund, H. P.; Li, Y. & Milton, S. V.
Partner: UNT Libraries Government Documents Department

Tabletop Transient Collisional Excitation X-Ray Lasers

Description: Recent transient collisional excitation x-ray laser experiments are reported using the COMET tabletop laser driver at the Lawrence Livermore National Laboratory (LLNL). Ne-like and Ni-like ion x-ray laser schemes have been investigated with a combination of long 600 ps and short {approximately}1 ps high power laser pulses with 5-10 J total energy. We show small signal gain saturation for x-ray lasers when a reflection echelon traveling wave geometry is utilized. A gain length product of 18 has been achieved for the Ni-like Pd 4d{r_arrow}4p J=0-1 line at 147 {angstrom}, with an estimated output of {approximately}10{micro}J. Strong lasing on the 119 {angstrom} Ni-like Sn line has also been observed. To our knowledge this is the first time gain saturation has been achieved on a tabletop laser driven scheme and is the shortest wavelength tabletop x-ray laser demonstrated to date. In addition, we present preliminary results of the characterization of the line focus uniformity for a Ne-like ion scheme using L-shell spectroscopy.
Date: September 3, 1999
Creator: Dunn, J.; Li, Y.; Osterheld, A. L; Nilsen, J.; Moon, S. J.; Fournier, K. B. et al.
Partner: UNT Libraries Government Documents Department

Laser-driven inner-shell excitation in high-Z atoms: A shell-selective impact ionization mechanism

Description: A highly selective, coherent impact ionization mechanism is proposed for the efficient generation of inner-shell population inversion in laser-driven plasmas. The theoretical analysis is consistent with observed L-shell (2p{l_arrow}3d) emission spectra from laser-excited Xe clusters.
Date: June 7, 2000
Creator: SCHROEDER,W. ANDREAS; NELSON,THOMAS R.; BORISOV,A.B.; LONGWORTH,J.W.; BOYER,K. & RHODES,C.K.
Partner: UNT Libraries Government Documents Department

Measurement of spatial gain profiles in multiple pulse driven Ne like Ge lasers

Description: We present the first direct spatial measurement of the two dimensional gain profiles for a Ne-like ion using a slab target illuminated by the multiple pulse technique. To understand the spatial dependence of the gain in Ne-like Ge on the 19.6 nm laser line for plasmas driven by a series of 100 ps pulses 400 ps apart we did a series of Nova experiments backlighting short Ge amplifiers. Two-dimensional, high-resolution, spatial images of the 19.6 nm laser emission from the output aperture of the amplifiers were measured to determine the spatial position of the gain. The amplifier lengths were chosen to be short enough to avoid significant refraction of the beam. In previous imaging experiments which measured the near field output of the Ge laser, the position of the laser output was dominated by refraction effects. To assure good temporal overlap, we used the traveling wave geometry to illuminate both the amplifier and backlighter. The amplifier design included a wire fiducial which provided an absolute spatial reference and avoided the usual difficulty of determining the location of the target surface. We compare the measured gain with simulations done using LASNEX, which calculates the hydrodynamic evolution of the plasma, and XRASER, which uses the temperature and densities from LASNEX to do the gain and kinetics calculations.
Date: June 1, 1997
Creator: Nilsen, J.; Moreno, J.C.; Barbee, T.W. & Da Silva, L.B.
Partner: UNT Libraries Government Documents Department

Edward Teller medal lecture: high intensity lasers and the road to ignition

Description: There has been much progress in the development of high intensity lasers and in the science of laser driven inertially confined fusion such that ignition is now a near term prospect. This lecture reviews the field with particular emphasis on areas of my own involvement.
Date: June 2, 1997
Creator: Key, M. H.
Partner: UNT Libraries Government Documents Department

An efficient, selective collisional ejection mechanism for inner-shell population inversion in laser-driven plasmas

Description: A theoretical analysis of laser-driven collisional ejection of inner-shell electrons is presented to explain the previously observed anomalous kilovolt L-shell x-ray emission spectra from atomic Xe cluster targets excited by intense sub-picosecond 248nrn ultraviolet radiation. For incident ponderomotively-driven electrons photoionized by strong above threshold ionization, the collisional ejection mechanism is shown to be highly l-state and significantly n-state (i.e. radially) selective for time periods shorter than the collisional dephasing time of the photoionized electronic wavefunction. The resulting preference for the collisional ejection of 2p electrons by an ionized 4p state produces the measured anomalous Xe(L) emission which contains direct evidence for (i) the generation of Xe{sup 27+}(2p{sup 5}3d{sup 10}) and Xe{sup 28+}(2p{sup 5}3d{sup 9}) ions exhibiting inner-shell population inversion and (ii) a coherent correlated electron state collision responsible for the production of double 2p vacancies. For longer time periods, the selectivity of this coherent impact ionization mechanism is rapidly reduced by the combined effects of intrinsic quantum mechanical spreading and dephasing--in agreement with the experimentally observed and extremely strong {minus}{lambda}{sup {minus}6} pump-laser wavelength dependence of the efficiency of inner-shell (2p) vacancy production in Xe clusters excited in underdense plasmas.
Date: June 7, 2000
Creator: SCHROEDER,W. ANDREAS; NELSON,THOMAS R.; BORISOV,A.B.; LONGWORTH,J.W.; BOYER,K. & RHODES,C.K.
Partner: UNT Libraries Government Documents Department

L-shell emission from high-Z solid targets by intense (10{sup 19}W/cm{sup 2}) irradiation with a 248nm laser

Description: Efficient (1.2% yield) multikilovolt x-ray emission from Ba(L) (2.4--2.8{angstrom}) and Gd(L) (1.7--2.1{angstrom}) is produced by ultraviolet (248nm) laser-excited BaF{sub 2} and Gd solids. The high efficiency is attributed to an inner shell-selective collisional electron ejection.
Date: November 22, 1999
Creator: Nelson, T. R.; Borisov, A. B.; Boyer, K.; Schroeder, W. A.; Santoro, J.; Van Tassle, A. J. et al.
Partner: UNT Libraries Government Documents Department

Progress in understanding the short-pulse-driven collisional x-ray lasers

Description: Recently, the technique of using a nsec pulse to preform and ionize the plasma followed by a psec pulse to heat the plasma has enabled low-Z neon-like and nickel-like ions to lase driven by small lasers with only ten joules of energy. In this work we model recent experiments done using the COMET laser at LLNL to illuminate I cm long slab targets of Ti with a 4.8 J, 800 ps prepulse followed 1.6 nsec later by a 6 J, 1 psec drive pulse. The LASNEX code is used to calculate the hydrodynamic evolution of the plasma and provide the temperatures and densities fo the XRASER code, which then does the kinetics calculations to determine the gain. The temporal and spatial evolution of the plasma is studied both with and without radiation transport included for the 3d and 3s (arrow) 2p Ne-like Ti resonance lines. Large regions with gains greater than 80 cm<sub>minus1</sub> are predicted for the 3p <sup>1</sup>S<sub>0</sub> (arrow), 3s <sup>1</sup>P,<sub>1</sub>Ne-like Ti laser line at 326 Å. Given the large gain and low gradients in these plasmas, we do propagation calculations including refraction to understand which regions have the right combination of high gain and low gradients to contribute to the X-ray laser output. Calculations are also presented using different delays between the long and short pulse and different widths for the short pulse to provide better insight for optimizing the laser output. In addition to the standard 326 Å laser line, high gain is also predicted and observed for the 3d <sup>1</sup>P<sub>1</sub> (arrow) 3p <sup>1</sup>P<sub>1</sub>, laser line at 301 Å in Ne-like Ti. We present calculations with and without radiation rransport included on the strong 3d <sup>1</sup>P<sub>1</sub> (arrow) 2p <sup>1</sup>S<sub>0</sub>, resonance line to better understand this self photopumping effect. We also look at the analog transition in Ni-like ...
Date: September 21, 1998
Creator: Nilsen, J.
Partner: UNT Libraries Government Documents Department

Characterization of a high-gain Ne-like Fe transient x-ray laser

Description: The authors present experimental results of a high efficiency Ne-like Fe transient collisional excitation x-ray laser using the COMET 15 TW table-top laser system at LLNL. The plasma formation, ionization and collision excitation of the x-ray laser have been optimized using two sequential laser pulses: a plasma formation beam with 5 J energy of 600 ps duration and a pump beam with 5 J energy of 1.2 ps duration. Since the observation of strong lasing on the 255 {angstrom} 3p-3s J = 0-1 transition of Ne-like Fe, they have achieved high gains of 35 cm{sup {minus}1} and saturation of the x-ray laser. A five-stage traveling wave excitation enhances the strongest Fe 3p-3s 255 {angstrom} lasing line as well as additional x-ray lines. A careful characterization of the plasma column conditions using L-shell spectroscopy indicates the degree of ionization along the line focus.
Date: September 13, 1999
Creator: Dunn, J; Facnov, A; Fournier, K B; Moon, S J; Osterheld, A; Pikuz, T et al.
Partner: UNT Libraries Government Documents Department

Inner-shell photoionized x-ray lasers

Description: The inner-shell photoionized x-ray lasing scheme is an attractive method for achieving x-ray lasing at short wavelengths, via population inversion following inner-shell photoionization (ISPI). This scheme promises both a short wavelength and a short pulse source of coherent x rays with high average power. In this dissertation a very complete study of the ISPI x-ray laser scheme is done concerning target structure, filter design and lasant medium. An investigation of the rapid rise time of x-ray emission from targets heated by an ultra-short pulse high-intensity optical laser was conducted for use as the x-ray source for ISPI x-ray lasing. Lasing by this approach in C at a wavelength of 45 {angstrom} requires a short pulse (about 50 fsec) driving optical laser with an energy of 1-5 J and traveling wave optics with an accuracy of {approximately} 15 {micro}m. The optical laser is incident on a high-Z target creating a high-density plasma which emits a broadband spectrum of x rays. This x-ray source is passed through a filter to eliminate the low-energy x rays. The remaining high-energy x rays preferentially photoionize inner-shell electrons resulting in a population inversion. Inner-shell photoionized x-ray lasing relies on the large energy of a K-{alpha} transition in the initially neutral lasant. The photo energy required to pump this scheme is only slightly greater than the photon energy of the lasing transition yielding a lasing scheme with high quantum efficiency. However, the overall efficiency is reduced due to low x-ray conversion efficiency and the large probability of Auger decay yielding an overall efficiency of {approximately} 10{sup {minus}7} resulting in an output energy of {micro}J's. They calculate that a driving laser with a pulse duration of 40 fs, a 10{micro}m x 1 cm line focus, and an energy of 1 J gives an effective gain length product (gl) ...
Date: June 1, 1998
Creator: Moon, S.J.
Partner: UNT Libraries Government Documents Department