Diode-laser-seeded optical parametric oscillator for airborne water vapor DIAL application in the upper troposphere and lower stratosphere

Received: 4 May 1998/Revised version: 17 July 1998     

Influence of a magnetic field on deposition of diamond-like carbon films

Received: 17 February 1998/Accepted: 25 May 1998     

Inverse metal-stripe polarizers

Received: 18 May 1998/Revised version: 17 August 1998     

Feedback-controlled optimization of amplified femtosecond laser pulses

Received: 17 December 1998     

Influence of cathode roughness on discharge homogeneity of a high-pulse repetition frequency long-pulse XeCl laser

Received: 17 October 1997/Revised version: 3 March 1998     

Quantum wires and quantum dots for neutral atoms

By placing changeable nanofabricated structures (wires, dots, etc.) on an atom mirror one can design guiding and trapping potentials for atoms. These potentials are similar to the electrostatic potentials which trap and guide electrons in semiconductor quantum devices like quantum wires and quantum dots. This technique will allow the fabrication of nanoscale atom optical devices. Received: 28 October 1997 / Revised: 17 February 1998 / Accepted: 17 July 1998     

Imaging within highly scattering media using time-resolved backscattering of femtosecond pulses

Received: 17 April 1998     

Generation of two-mode quadrature-phase squeezing and intensity-difference squeezing from a cw-NOPO

Received: 17 January 1998     

Prompt electron emission and collisional ionization of ambient gas during pulsed laser ablation of silver

17 cm^-3 and it is found that the density increases as a function of distance away from the target. Dependence of probe current on laser intensity shows plasma shielding at high laser intensities. Received: 5 January 1998/Accepted: 3 July 1998     

Estimation of trap concentration in photorefractive crystals by a technique of adaptive holographic interferometry

12 GeO₂₀, Bi₁₂SiO₂₀, Bi₁₂TiO₂₀). Received: 17 June 1998/Revised version: 3 August 1998     

The 1D spin- AF-Heisenberg model in a staggered field

We investigate the scaling properties of the excitation energies and transition amplitudes of the one-dimensional spin- antiferromagnetic Heisenberg model exposed to an external perturbation. Two types of perturbations are discussed in detail: a staggered field and a dimerized field. Received: 27 February 1998 / Accepted: 17 April 1998     

Temperature corrections to conformal field theory

We consider finite temperature dynamical correlation functions in the interacting delta-function Bose gas. In the low-temperature limit the asymptotic behaviour of correlation functions can be determined from conformal field theory. In the present work we determine the deviations from conformal behaviour at low temperatures. Received: 14 January 1998 / Accepted: 17 March 1998     

Quantum statistical mechanics of ideal gas obeying fractional exclusion statistics: a systematic study

The quantum statistical mechanics of an ideal gas with a general free-particle energy obeying fractional exclusion statistics are systematically investigated in arbitrary dimensions. The pressure relations, the relation between pressure and internal energy, the equation of state, as well as the thermodynamic properties are thoroughly discussed. Some novel results are obtained. Received: 23 January 1998 / Accepted: 17 March 1998     

Field theoretical calculation of the specific heat exponent for a classical N-vector model in a random external field

We calculate using diagrammatic perturbation theory in the two-loop approximation, the specific heat exponent for the classical N-vector model in a random external field for spatial dimension (D) lying between four and six. The calculation supports the modified hyperscaling , where is the correlation length exponent. Received: 18 March 1998 / Revised: 17 April 1998 / Accepted: 21 April 1998     

Critical behavior of interacting surfaces with tension

Wetting phenomena, molecular protrusions of lipid bilayers and membrane stacks under lateral tension provide physical examples for interacting surfaces with tension. Such surfaces are studied theoretically using functional renormalization and Monte-Carlo simulations. The critical behavior arising from thermally-excited shape fluctuations is determined both for global quantities such as the mean separation of these surfaces and for local quantities such as the probabilities for local contacts. Received: 30 January 1998 / Accepted: 17 March 1998     

Two-parameter extended Hubbard Hamiltonian with supersymmetry

We investigate under which circumstances extended Hubbard models, including bond-charge, exchange, and pair-hopping terms, are invariant under gl (2,1) superalgebra. This happens for a two-parameter Hamiltonian which includes as particular cases the t - J, the EKS and the one-parameter BGLZ Hamiltonians, all integrable in one dimension. We show that the two parameter Hamiltonian can be recasted as the sum of the BGLZ Hamiltonian plus the graded permutation operator of electronic states on neighbouring sites. The integrability of the corresponding one-dimensional model is discussed. Received: 17 February 1998 / Received in final form: 6 March 1998 / Accepted: 17 April 1998     

Spontaneous SU(2) symmetry breaking in one-dimensional quantum antiferromagnet

We present a Bethe Ansatz based investigation of a one-dimensional (1D) Heisenberg spin chain in a real 3D crystal lattice. We have shown that due to an influence of the lattice distortion on a crystalline field of ligands of magnetic ions, a Heisenberg antiferromagnetic spin chain is unstable under the appearance of a magnetic anisotropy of the “easy-plane” type. The effects of an external magnetic field and nonzero temperature onto such a phase transition are studied. Received: 19 January 1998 / Revised: 16 March 1998 / Accepted: 17 March 1998     

Microscopic conditions favoring itinerant ferromagnetism: Hund's rule coupling and orbital degeneracy

The importance of Hund's rule coupling for the stabilization of itinerant ferromagnetism is investigated within a two-band Hubbard model. The magnetic phase diagram is calculated by finite-temperature quantum Monte-Carlo simulations within the dynamical mean-field theory. Ferromagnetism is found in a broad range of electron fillings whereas antiferromagnetism exists only near half filling. The possibility of orbital ordering at quarter filling is also analyzed. Received: 26 February 1998 / Accepted: 17 April 1998     

Characterization of photorefractive materials by spontaneous noncolinear frequency doubling

‘Spontaneous’ noncolinear frequency doubling (SNCFD) is a type of optical second-harmonic generation (SHG) that uses scattered light to provide additional fundamental beams in order to accomplish noncolinear phase matching. Based on a novel algorithm for the automated evaluation of the resulting ring patterns, we present an easy-to-apply, sensitive, and non-destructive method for the characterization of photorefractive materials, yielding two-dimensional spatial resolution. As applications of the technique, examples for the characterization of lithium niobate crystals are presented. Received: 30 October 1998 / Revised version: 17 December 1998 / Published online: 7 April 1999