Shortening of excimer laser pulses with saturable absorbers

Shortening by a factor of more than five of XeCl laser pulses by a single pass saturable absorber is recorded. The pulse shortening is attributed to the combined action of both nonlinear absorption and stimulated emission from the dye solution.     

Two-wavelength operation of a femtosecond ring dye laser

We report on two-wavelength operation of a CPM ring dye laser employing Rhodamine 6G as gain medium and a new styryl dye as saturable absorber. Two trains of femtosecond pulses at different wavelengths are simultaneously generated under proper alignment of the laser. The secondary pulse train is attributed to the laser action of the absorber dye. Auto- and cross-correlation measurements are performed to determine the temporal characteristics of the laser in the double mode-locking regime.     

Theory of a ‘time telescope’

An analysis of an optical system for the magnification of ultrashort light pulses is presented. It consists of a series of time dispersive elements and acts as a pair of lenses (telescope) in time. Such a device would permit a direct measurement of the intensity profiles and durations of picosecond and femtosecond pulses instead of using autocorrelation estimations.     

Recent test and new applications of the unified theory of electron emission

A review is presented of the recent experimental research confirming the unified theory of electron emission from metals in vacuum, insulators and semiconductors in the whole range between the extreme conditions of field and thermionic emission. Some new applications of the theory for calculation of the electron current in vacuum discharge, for determination of the metal-insulator (semiconductor) work function and for estimation of the effective (conduction band) electron mass in insulators and semiconductors, are also considered.     

The excitation of spectral lines in the cold cathode region of a glow discharge in argon

Calculations on the excitation of spectral lines emitted by the cathode fall and the negative glow regions of a glow discharge in argon have been performed using space-dependent electron velocity distributions allowing for electron impact excitation and ionization of atoms.     

Comments on: “Energetic balance for the Rayleigh–Stokes problem of an Oldroyd-B fluid” [Nonlinear Anal. RWA 12 (2011) 1]

We point out that an erroneous derivation in the recent paper [C. Fetecau et al. Energetic balance for the Rayleigh–Stokes problem of an Oldroyd-B fluid, Nonlinear Anal. RWA 12 (2011) 1–13] yields a correct solution by accident. Additionally, a number of misrepresentations and inaccuracies in the latter recent paper are identified, corrected and/or clarified in this Comment. Finally, a listing of recent papers in this journal in which a mistake occurs while applying the Fourier sine transform, and thus present erroneous solutions, is given as an Appendix.     

Correlated electron dynamics with time-dependent quantum Monte Carlo: three-dimensional helium

Here the recently proposed time-dependent quantum Monte Carlo method is applied to three dimensional para- and ortho-helium atoms subjected to an external electromagnetic field with amplitude sufficient to cause significant ionization. By solving concurrently sets of up to 20,000 coupled 3D time-dependent Schro?dinger equations for the guide waves and corresponding sets of first order equations of motion for the Monte Carlo walkers we obtain ground state energies in close agreement with the exact values. The combined use of spherical coordinates and B-splines along the radial coordinate proves to be especially accurate and efficient for such calculations. Our results for the dipole response and the ionization of an atom with un-correlated electrons are in good agreement with the predictions of the conventional time-dependent Hartree-Fock method while the calculations with correlated electrons show enhanced ionization that is due to the electron-electron repulsion.     

Alkatrienyl Sulfoxides and Sulfones,VIII: Diels–Alder Reaction of 3‐Methylpenta‐1,2,4‐trienyl Phenyl Sulfoxide with Maleic Anhydride

Regio‐and stereo‐selective Diels–Alder reaction of 3‐methylpenta‐1,2,4‐trienyl phenyl sulfoxide with maleic anhydride in the absence or presence of a Lewis acid as catalyst with formation of sulfinyl‐substituted benzofuran or norbornene cycloadducts, respectively, is described.     

Investigation of the magnetic properties of the Fe2-xCrxCaO4 system

Conclusions Due to the fact that the iron ions in two neighbouring elementary cells along the c-axis are in symmetry positions in relation to the oxygen anion (through which the interaction with other iron ions is achieved), the stronger 120° and 130° interactions could be considered as interactions not by zigzag-formed chains, but by the folded planes with c-axis as a generant, i.e., the quasi-twodimensional magnetic properties are evinced in Cr_xFe_2–xCaO₄.