High-energy laser-pulse self-compression in short gas-filled fibers

We examine the spatiotemporal compression of energetic femtosecond laser pulses within short gas-filled fibers. The study is undertaken using an advanced nonlinear pulse propagation model based on a multimode generalized nonlinear Schrödinger equation that has been modified to include plasma effects. Plasma defocusing and linear propagation effects are shown to be the dominant processes within a highly dynamical mechanism that enables 100-fs pulses to be compressed into the few-cycle regime after <50 mm of propagation. Once the mechanism has been introduced, parameter spaces are explored and compressor designs suitable for performing high-field experiments in situ are presented. We finish by showing how these designs may be extended to novel wavelengths and driving pulses delivered by state-of-the-art high-repetition-rate lasers

Experimental demonstration of a high-flux capillary based XUV source in the high ionisation regime

High harmonic generation (HHG) has proven to be a fascinating and incredibly useful nonlinear optical phenomenon and has led to the realisation of tabletop sources of coherent extreme ultraviolet (XUV) radiation. Capillary based geometries in particular have attracted a great deal of attention due to their lengthy interaction regions and the potential to phase-match the HHG process leading to a large increase in XUV flux. Unfortunately due to plasma induced nonlinear and dispersive effects the simple phase-matching mechanism detailed in [1] cannot be scaled to high energy pump pulses and high gas pressures. In this work we have used a computational model [2] to design a capillary that can support a broad interaction region well-suited to quasi-phase-matching (QPM) while simultaneously reducing the effect that XUV reabsorption has on the output flux of the source. This modelling work has involved adjusting both the capillary length and gas density profile (figure 1a) in order to produce rapid oscillations in the radially integrated ionization fraction (figure 1b) coupled with a rapid decrease in gas pressure at the capillary exit. Our theory suggests that these oscillations are driven by a nonlinear self-compression process modulating the intensity of the pump pulse as it propagates through the plasma-filled waveguide [3]. Subsequent experimental work has shown an increase in XUV flux of almost 50 times over our previous capillary-based source (see figure 1c), and preliminary estimates suggest a photon flux of 1012 photons s-1 harmonic-1 in the 45 eV spectral region

Statistical analysis of pump-pulse propagation in gas-filled capillaries for high-harmonic generation

Driving high-harmonic generation (HHG) with ultrashort pulses confined to gas-filled capillaries is an efficient method of generating extreme ultraviolet and x-ray radiation. In-situ pulse compression can significantly enhance HHG efficiency [1] but requires operation in the high-ionisation limit, leading to high sensitivity to initial conditions and causing the Gaussian driving pulse to break up into a train of subpulses as it propagates. Our previous studies [1,2] have focused on the most intense subpulse, which can be very short (<10 fs). Here, we perform statistical analysis of all pulse components predicted by numerical simulation, including the contribution of the weaker subpulses, with the aim of predicting generated HHG profiles

Z' Decays into Four Fermions

If a new $Z'$ is discovered with a mass $\sim 1 \ TeV$ at LHC/SSC, its (rare) decays into two charged leptons plus missing transverse energy will probe the $Z'$ coupling to the lepton doublet $(\nu,e)_L$ and to $W^+W^-$, allowing further discrimination among extended electroweak models.Comment: 9 pages plus 1 figure (not included but available), UG-FT-22/9

Statistics of Coulomb blockade peak spacings for a partially open dot

We show that randomness of the electron wave functions in a quantum dot contributes to the fluctuations of the positions of the conductance peaks. This contribution grows with the conductance of the junctions connecting the dot to the leads. It becomes comparable with the fluctuations coming from the randomness of the single particle spectrum in the dot while the Coulomb blockade peaks are still well-defined. In addition, the fluctuations of the peak spacings are correlated with the fluctuations of the conductance peak heights.Comment: 13 pages, 1 figur

The Case for Message Passing on Many-Core Chips

Coordinated Science Laboratory was formerly known as Control Systems LaboratoryUILU-ENG-10-2203, CRHC-10-0

Beyond the Shade of the Oak Tree: The Recent Growth of Johannine Studies

The recent growth within Johannine studies has developed as a result of several factors. First, the discovery of the Dead Sea Scrolls led to an appreciation of the Jewishness of John’s origin. Second, new approaches to John’s composition have emerged, followed by a larger set of inquiries as to the Johannine tradition’s relation to parallel traditions. This has been accompanied by a fourth interest: the history of the Johannine situation. Fifth, new literary studies have posed new horizons for interpretation, and sixth, theories continue to abound on the identity of the Beloved Disciple. A seventh development involves new ways of conceiving John’s theological features, leading to an eighth: reconsidering John’s historical features and re-envisioning its historical contributions in new perspective

Post-Newtonian Gravitational Radiation

1 Introduction 2 Multipole Decomposition 3 Source Multipole Moments 4 Post-Minkowskian Approximation 5 Radiative Multipole Moments 6 Post-Newtonian Approximation 7 Point-Particles 8 ConclusionComment: 46 pages, in Einstein's Field Equations and Their Physical Implications, B. Schmidt (Ed.), Lecture Notes in Physics, Springe

Jamming at Zero Temperature and Zero Applied Stress: the Epitome of Disorder

We have studied how 2- and 3- dimensional systems made up of particles interacting with finite range, repulsive potentials jam (i.e., develop a yield stress in a disordered state) at zero temperature and applied stress. For each configuration, there is a unique jamming threshold, $\phi_c$, at which particles can no longer avoid each other and the bulk and shear moduli simultaneously become non-zero. The distribution of $\phi_c$ values becomes narrower as the system size increases, so that essentially all configurations jam at the same $\phi$ in the thermodynamic limit. This packing fraction corresponds to the previously measured value for random close-packing. In fact, our results provide a well-defined meaning for "random close-packing" in terms of the fraction of all phase space with inherent structures that jam. The jamming threshold, Point J, occurring at zero temperature and applied stress and at the random close-packing density, has properties reminiscent of an ordinary critical point. As Point J is approached from higher packing fractions, power-law scaling is found for many quantities. Moreover, near Point J, certain quantities no longer self-average, suggesting the existence of a length scale that diverges at J. However, Point J also differs from an ordinary critical point: the scaling exponents do not depend on dimension but do depend on the interparticle potential. Finally, as Point J is approached from high packing fractions, the density of vibrational states develops a large excess of low-frequency modes. All of these results suggest that Point J may control behavior in its vicinity-perhaps even at the glass transition.Comment: 21 pages, 20 figure