197 research outputs found
Optimization of double drive pulse pumping in Ne-like Ge x-ray lasers
Pumping of the Ne-like Ge x-ray laser with two 100 ps duration pulses (a prepulse and main pulse) is investigated using a fluid and atomic physics code coupled to a 3D ray tracing postprocessor code. The modeling predicts the optimum ratio of the irradiance of the two pulses for the maximum x-ray laser output resulting from the balance between the relative lower electron density gradients and wider gain region which is produced with a larger prepulse and the higher peak gain coefficients produced with a small prepulse. With a longer pulse interval between prepulse and main pulse, a relatively lower optimum pulse ratio is found. The threshold irradiance of the main driving pulse with a prepulse required to make an order of magnitude enhancement of laser output compared to irradiation without a prepulse is also found at 3-4x10(13) W/cm(2) for Ne-like Ge. (C) 1998 American Institute of Physics
Optimization of double pulse pumping for Ni-like Sm x-ray lasers
We report a systematic study of double pulse pumping of the Ni-like Sm x-ray laser at 73 Angstrom, currently the shortest wavelength saturated x-ray laser. It is found that the Sm x-ray laser output can change by orders of magnitude when the intensity ratio of the pumping pulses and their relative delay are varied. Optimum pumping conditions are found and interpreted in terms of a simple model. (C) 1999 American Institute of Physics. [S0021-8979(99)07102-9]
Ablation of Submicrometer Holes Using an Extreme-Ultraviolet Laser
Simulations and experiments are used to study extreme-ultraviolet (EUV) laser drilling of submicrometer holes. The ablation process is studied with a 2D Eulerian hydrodynamic code that includes bound-free absorption processes relevant to the interaction of EUV lasers with a solid material. Good agreement is observed between the simulated and measured ablated depths for on-target irradiances of up to 1×1010  W cm−2. An increase in the irradiance to 1×1012  W cm−2 is predicted to ablate material to a depth of 3.8  μm from a single pulse with a hole diameter 3 to 4 times larger than the focal spot size. The model allows for the simulation of the interaction of a laser pulse with the crater created by a previous shot. Multiple-pulse lower-fluence irradiation configurations under optimized focusing conditions, i.e., approaching the diffraction limit, are shown to be advantageous for applications requiring mesoscale [(100  nm)–(1  μm)] features and a high level of control over the ablation profile
A review of X-ray laser development at Rutherford Appleton Laboratory
Recent experiments undertaken at the Rutherford Appleton Laboratory to produce X-ray lasing over the 5-30 nm wavelength range are reviewed. The efficiency of lasing is optimized when the main pumping pulse interacts with a preformed plasma. Experiments using double 75-ps pulses and picosecond pulses superimposed on 300-ps background pulses are described. The use of travelling wave pumping with the approximately picosecond pulse experiments is necessary as the gain duration becomes comparable to the time for the X-ray laser pulse to propagate along the target length. Results from a model taking account of laser saturation and deviations from the speed of light c of the travelling wave and X-ray laser group velocity are presented. We show that X-ray laser pulses as short as 2-3 ps can be produced with optical pumping pulses of approximate to1-ps
Ablation and transmission of thin solid targets irradiated by intense extreme ultraviolet laser radiation
The interaction of an extreme ultraviolet (EUV) laser beam with a parylene foil was studied by experiments and simulation. A single EUV laser pulse of nanosecond duration focused to an intensity of 3 × 1010 W cm−2 perforated micrometer thick targets. The same laser pulse was simultaneously used to diagnose the interaction by a transmission measurement. A combination of 2-dimensional radiation-hydrodynamic and diffraction calculations was used to model the ablation, leading to good agreement with experiment. This theoretical approach allows predictive modelling of the interaction with matter of intense EUV beams over a broad range of parameters
Enhanced He-alpha emission from "smoked" Ti targets irradiated with 400nm, 45 fs laser pulses
We present a study of He-like 1s(2)-1s2p line emission from solid and low-density Ti targets under similar or equal to 45 fs laser pulse irradiation with a frequency doubled Ti: Sapphire laser. By varying the beam spot, the intensity on target was varied from 10(15) W/cm(2) to 10(19) W/cm(2). At best focus, low density "smoked" Ti targets yield similar to 20 times more He-alpha than the foil targets when irradiated at an angle of 45 degrees with s-polarized pulses. The duration of He-alpha emission from smoked targets, measured with a fast streak camera, was similar to that from Ti foils
The creation of radiation dominated plasmas using laboratory extreme ultra-violet lasers
Ionization in experiments where solid targets are irradiated by high irradiance extreme ultra-violet (EUV) lasers is examined. Free electron degeneracy effects on ionization in the presence of a high EUV flux of radiation is shown to be important. Overlap of the physics of such plasmas with plasma material under compression in indirect inertial fusion is explored. The design of the focusing optics needed to achieve high irradiance (up to 1014 Wcm−2) using an EUV capillary laser is presented
Two-photon Lithography for 3D Magnetic Nanostructure Fabrication
Ferromagnetic materials have been utilised as recording media within data
storage devices for many decades. Confinement of the material to a two
dimensional plane is a significant bottleneck in achieving ultra-high recording
densities and this has led to the proposition of three dimensional (3D)
racetrack memories that utilise domain wall propagation along nanowires.
However, the fabrication of 3D magnetic nanostructures of complex geometry is
highly challenging and not easily achievable with standard lithography
techniques. Here, by using a combination of two-photon lithography and
electrochemical deposition, we show a new approach to construct 3D magnetic
nanostructures of complex geometry. The magnetic properties are found to be
intimately related to the 3D geometry of the structure and magnetic imaging
experiments provide evidence of domain wall pinning at a 3D nanostructured
junction
The Creation of Radiation Dominated Plasmas Using Laboratory X-Ray Lasers
When short wavelength extreme ultraviolet (EUV) and X-ray laser radiation is focused onto solid targets, narrow deep features are ablated and a dense, low-temperature plasma is formed. We examine the radiation dominated plasma formed by 46.9 nm laser radiation focused onto solids and show that ionisation can be significantly modified by electron degeneracy effects. Some experimental and theoretical considerations for investigating the interaction of capillary discharge lasers operating at 46.9 nm with solid and gas targets are presented
Local and global Fokker-Planck neoclassical calculations showing flow and bootstrap current modification in a pedestal
In transport barriers, particularly H-mode edge pedestals, radial scale
lengths can become comparable to the ion orbit width, causing neoclassical
physics to become radially nonlocal. In this work, the resulting changes to
neoclassical flow and current are examined both analytically and numerically.
Steep density gradients are considered, with scale lengths comparable to the
poloidal ion gyroradius, together with strong radial electric fields sufficient
to electrostatically confine the ions. Attention is restricted to relatively
weak ion temperature gradients (but permitting arbitrary electron temperature
gradients), since in this limit a delta-f (small departures from a Maxwellian
distribution) rather than full-f approach is justified. This assumption is in
fact consistent with measured inter-ELM H-Mode edge pedestal density and ion
temperature profiles in many present experiments, and is expected to be
increasingly valid in future lower collisionality experiments. In the numerical
analysis, the distribution function and Rosenbluth potentials are solved for
simultaneously, allowing use of the exact field term in the linearized
Fokker-Planck collision operator. In the pedestal, the parallel and poloidal
flows are found to deviate strongly from the best available conventional
neoclassical prediction, with large poloidal variation of a different form than
in the local theory. These predicted effects may be observable experimentally.
In the local limit, the Sauter bootstrap current formulae appear accurate at
low collisionality, but they can overestimate the bootstrap current near the
plateau regime. In the pedestal ordering, ion contributions to the bootstrap
and Pfirsch-Schluter currents are also modified
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