Most models of intracavity oscillators based on nonlinear optical frequency conversion expand resonating fields in a set of cavity normal modes, the so-called Slater normal-mode expansion (NME) method. Such an approach normally yields slow variation of field amplitude, on the scale of the cavity's round-trip time. To study faster amplitude oscillations, the authors derive the time-delay (TD) model of intracavity nonlinear optical interaction. Their model should foster a deeper understanding of the dynamics of intracavity optical parametric oscillators and difference-frequency generators, devices that are almost ideal for high-resolution spectroscopy in the midinfrared spectral window.
<p>Complex structure of a skeleton of saturated porous medium can have a great influence on the processes of heat and mass transfer.<span>&#160;</span></p><p>There are various approaches to the description of<span>&#160; </span>two-phase flow: direct numerical calculation of fluid flow in the pore space, multicontinuous models with the laws of mass exchange between continua, single-continuum models of non-equilibrium flow.&#160;In the family of isothermal non-equilibrium filtration models, the relative phase permeabilities and capillary pressure are functions not of current saturation but of their change history.</p><p>In this work we generalize the relaxation model of capillary nonequilibrium to the non-isothermal case. We introduce two internal thermodynamic parameters (capillary and thermal nonequilibrium) which depend on change history of saturation and temperature. In the model relative phase permeabilities and capillary pressure are functions of saturation, temperature, and current values of these internal parameters. Based on the analysis of the dissipation inequality, thermodynamically consistent kinetic equations for the evolution of these parameters are proposed. The parameters of the single-continuum model are clarified with double-porosity model of porous media with special structure. Structure of the penetration front of fluid hot (or cold) compared to the skeleton was investigated.</p><p>This work was supported by the Russian Foundation for Basic Research: grant N19-01-00592.<span>&#160;</span></p><p>&#160;</p>
A novel method to increase the pulse repetition rate by means of fission of second-order solitons in the fiber with periodically modulated dispersion is studied. The experiments confirm the results of numerical simulations. The efficient doubling of the pulse repetition rate takes place in dispersion oscillating fiber (DOF). Good agreement between theory and experiment was obtained.
A single-mode fiber with a sinusoidal variation of the core diameter was fabricated. The soliton splitting due to the longitudinal oscillation of the fiber dispersion is demonstrated experimentally. The experimental observations are confirmed through numerical simulations. The periodical modulation of the fiber dispersion can be used for controlling the soliton splitting even under the strong effect of the Raman scattering.
Chalcogenide glasses are novel highly non-linear materials for photonics. Modification of optical glasses by high-intensity femtosecond pulses is a novel fast developing technology based on non-linear effects. In this paper, the advantages of using the method of femtosecond modifications for the fabrication of highly non-linear 3D photonic structures in bulk chalcogenide glasses are overviewed. Design and modelling of chip-scale highly non-linear structures for all-optical signal processing are discussed.
Abstract We found that pre-chirp of initial pulses allows to control both the fission and fusion of solitons in dispersion oscillating fiber characterized by a sinusoidally varying group velocity dispersion. The fission of second order solitons and collision of two co-propagated solitons are considered. It is shown that initial chirp can prevent the resonant fission of second order soliton into two pulses propagating with different group velocities. Inelastic collision of two in-phase solitons is found can be quite different, when the chirp imposed on initial pulses. The soliton transformation reflects in the set of output eigenvalues of the Zakharov–Shabat spectral problem. Manipulation of the input pulse chirp allows to control both real and imaginary parts of the eigenvalues at the output of the fiber.
The major role in supercontinuum generation by laser pulses play dispersive wave generation and four-wave mixing. We propose to modify the phase-matching conditions for dispersive wave and four-wave mixing by periodical modulation of the diameter of microstructured fiber. Periodical modulation of the fiber diameter leads to variation of propagation constant. As result the phase-matching conditions for dispersive wave radiation and four-wave mixing become modified.
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