Black-body radiation of noncommutative gauge fields

The black-body radiation is considered in a theory with noncommutative electromagnetic fields; that is noncommutativity is introduced in field space, rather than in real space. A direct implication of the result on cosmic microwave background map is argued.     

Systematics of inner-shell photo-ionization X-ray lasers with constant pump rates

Population-rate equations are analytically solved for constant pump rates. Conditions for population inversions are developed for this simplified case. Numbers appropriate for inner-shell photo-ionization of magnesium and neon are used. These allow back-of-the envelope calculations for predicting lasing duration. Pump-rate thresholds are also given which permit lasing for the duration of the pumping. Blackbody-source temperatures associated with such pump rates are calculated. A method of using the solution of the small-signal population-rate equations to determine the saturated intensity when the lower lasing level has a decay channel is given. This method is applied to the case of constant pump rates. An analytic expression for the saturated intensity is developed for this case.     

Verification of X-ray line coincidences by high-resolution spectroscopy

Photo-resonant pumping of X-ray lasers requires close coincidence of a strong emission line with a suitable absorbing transition. We use a high-resolution crystal spectrometer to verify five coincidences, one of which has apparently not yet appeared in published work. All but one of the coincidences are found to lie within one linewidth. With respect to X-ray laser photo-pumping three of the five coincidences seem to be promising candidates.     

GLF - A simulation code for X-ray lasers

This paper describes the multi-dimensional Non-Local Thermodynamic Equilibrium (NLTE) simulation code GLF. GLF simulates those physical processes needed for modeling X-ray lasers: atomic kinetics, radiation transport, hydrodynamics and basic laser-plasma interactions. GLF is constructed to be modular, portable and efficient. This paper concentrates on the physical formulations and numerical methods used in GLF.     

Drift of gases induced by nonmonochromatic light

The phenomenon of light-induced drift of gases influenced by a nonmonochromatic light with different spectral properties is under consideration. The dependence of the drift velocity on the spectrum shape, bandwidth, detunings and light intensity is studied. The largest drift velocity is found to be obtained at the bandwidth of the spectrum being of the order of the Doppler atomic transition width, and when the wings of the spectrum drop rapidly. It is shown that nonmonochromatic light of the same intensity as a monochromatic one allows to reach a much larger drift velocity. Principal possibilities to obtain supersonic light-induced drift velocities are shown.     

Phasematching of frequency-conversion processes induced by additional selective pump

Possibility to induce phasematching in gaseous nonlinear media with the help of additional pumping of a proper energy level of atoms is shown.     

Conditions for XUV amplification considering recombination in clusters

3 cm^-l for a wavelength of λ_R≈200 Å in a time ≲1 ps can be expected. The measurable gain G_real depends on the cluster density N_cl. For N_cl≈10¹⁶ cm^-3 we expect G_real≳20 cm^-1. Received: 30 October 1997     

Enhancement of Ne-like Ar 46.9 nm laser output by mixing appropriate He ratio at low pressure

With pure Ar and gaseous mixtures of Ar-He, the laser spike of Ne-like Ar 46.9 nm pumped by capillary discharge is measured with XRD (X-ray diode) at low pressure. We observe the effects of the Ar pressure and the He ratio on the amplitude of laser pulse. Compared with the laser spike of pure Ar, a mixture of Ar and a small quantity of He enhances the laser output. The time of lasing onset and the duration of laser pulses are not affected by mixing He. In addition, a monochromator is used to measure the laser pulse at 46.9 nm. This is the first observation of laser output with a Ar-He mixture.     

Neutron- and muon-induced background in underground physics experiments

Background induced by neutrons in deep underground laboratories is a critical issue for all experiments looking for rare events, such as dark matter interactions or neutrinoless ββ decay. Neutrons can be produced either by natural radioactivity, via spontaneous fission or (α, n) reactions, or by interactions initiated by high-energy cosmic rays. In all underground experiments, Monte Carlo simulations of neutron background play a crucial role for the evaluation of the total background rate and for the optimization of rejection strategies. The Monte Carlo methods that are commonly employed to evaluate neutron-induced background and to optimize the experimental setup, are reviewed and discussed. Focus is given to the issue of reliability of Monte Carlo background estimates. We dedicate this work to the memory of our friend and colleague Nicola Ferrari, who prematurely passed away in July 2006.