New resonant emission of dispersive waves by oscillating solitary structures in optical fiber cavities is considered analytically and numerically. The pulse propagation is described in the framework ...of the Lugiato-Lefever equation when a Hopf-bifurcation can result in the formation of oscillating dissipative solitons. The resonance condition for the radiation of the dissipative oscillating solitons is derived and it is demonstrated that the predicted resonances match the spectral lines observed in numerical simulations perfectly. The complex recoil of the radiation on the soliton dynamics is discussed. The reported effect can have importance for the generation of frequency combs in nonlinear microring resonators.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We study theoretically a possibility of creation and ultrafast control (erasing, spatial frequency multiplication) of population density gratings in a multi-level resonant medium having a resonance ...transition frequency in the THz range. These gratings are produced by subcycle THz pulses coherently interacting with a nonlinear medium, without any need for pulses to overlap, thereby utilizing an indirect pulse interaction via an induced coherent polarization grating. High values of dipole moments of the transitions in the THz range facilitate low field strength of the needed THz excitation. Our results clearly show this possibility in multi-level resonant media. Our theoretical approach is based on an approximate analytical solution of time-dependent Schrödinger equation (TDSE) using perturbation theory. Remarkably, as we show here, quasi-unipolar subcycle pulses allow more efficient excitation of higher quantum levels, leading to gratings with a stronger modulation depth. Numerical simulations, performed for THz resonances of the Formula: see text molecule using Bloch equations for density matrix elements, are in agreement with analytical results in the perturbative regime. In the strong-field non-perturbative regime, the spatial shape of the gratings becomes non-harmonic. A possibility of THz radiation control using such gratings is discussed. The predicted phenomena open novel avenues in THz spectroscopy of molecules with unipolar and quasi-unipolar THz light bursts and allow for better control of ultra-short THz pulses.
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We provide Python tools enabling numerical simulation and analysis of the propagation dynamics of ultrashort laser pulses in nonlinear waveguides. The modeling approach is based on the widely used ...generalized nonlinear Schrödinger equation for the pulse envelope. The presented software implements the effects of linear dispersion, pulse self-steepening, and the Raman effect. The focus lies on the implementation of input pulse shot noise, i.e. classical background fields that mimic quantum noise, which are often not thoroughly presented in the scientific literature. We discuss and implement commonly adopted quantum noise models based on pure spectral phase noise, as well as Gaussian noise. Coherence properties of the resulting spectra can be calculated. We demonstrate the functionality of the software by reproducing results for a supercontinuum generation process in a photonic crystal fiber, documented in the scientific literature. The presented Python tools are open-source and released under the MIT license in a publicly available software repository.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We demonstrate a novel method for supercontinuum generation in an optical fiber based on two-color pumping with a delay and a group velocity matching. The scheme relies on the enhanced ...cross-phase-modulation at an intensity induced refractive index barrier between a dispersive wave and a soliton. The generation mechanism neither incorporates soliton fission nor a modulation instability and therefore exhibits extraordinary coherence properties, enabling the temporal compression of octave bandwidth into a short pulse. Moreover, the properties of the supercontinuum are adjustable over a wide range in the frequency domain by suitable choice of the dispersive wave.
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We present a Python toolkit for simulating the propagation dynamics of dissipative solitons in a variant of the Lugiato–Lefever equation (LLE) including dispersion terms of third and fourth order. In ...addition, the provided software allows to prepare initial conditions given by stationary localized solutions of the standard LLE in the anomalous group-velocity dispersion regime. Propagation scenarios for custom control parameters and initial conditions can be specified by the user via a simple class data structure. We demonstrate the implemented functionality by showing how to obtain stationary solutions of the standard LLE containing a dissipative soliton, and, demonstrating different characteristic propagation scenarios. The pyGLLE software package is open-source and released under the X11 License in a publicly available software repository.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Recent measurements of time delays during tunnelling of cold atoms through an optically created potential barrier have fuelled an ongoing debate about possible time delays during light-induced ...tunnelling of an electron from an atom. Yet, such a delay—whether it is present or not—is only one quantity characterizing the tunnelling wavepacket, whilst the underlying dynamics are richer. Here we show how to complement photo-electron detection in laser-induced tunnelling by measuring the light emitted by the tunnelling electron—the so-called Brunel radiation. Using a combination of single- and two-colour driving fields, we identify the all-optical signatures of the reshaping of the tunnelling wavepacket as it emerges from the tunnelling barrier and moves away from the core. This reshaping includes not only an effective time delay but also the time-reversal asymmetry of the ionization process, which we describe theoretically and observe experimentally. We show how both delay and reshaping are mapped onto the polarization properties of the Brunel radiation, with different harmonics behaving as different hands of a clock moving at different speeds. The all-optical detection may also allow time-resolved measurements of optical tunnelling in condensed matter systems on the attosecond time scale.Whether or not an electron wavepacket accumulates a time delay when tunnelling out of an atom is still under debate. Improved all-optical characterization of the tunnelling dynamics by combining one- and two-colour driving fields may shed light on this question.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A procedure for computation of the nonlinear refractive index of a gaseous medium from the intensity dependence of the ionization rate is reported. The ionization rate is calculated from Keldysh ...theory via a Kramers-Kronig transform. Peremolov-Popov-Terent'ev (PPT) theory is analyzed in the perturbative limit of multiphoton ionization for a completely analytical expression for the nonlinear refractive index. The method requires knowledge of only the particle density and the ionization energy of the gas. Example calculations are performed for the inert gases and compared to experimental data and atomic model calculations for the hyperpolarizability of the respective media. Excellent agreement between reference data and the computed values derived from the Kramers-Kronig transform is found in the visible and infrared spectral range. Additionally, higher-order nonlinear refraction is discussed.
The optical properties of metallic nanoparticles are most often considered in terms of plasmons, the coupled states of light and quasifree electrons. Confinement of electrons inside the nanostructure ...leads to another, very different type of resonances. We demonstrate that these confinement-induced resonances typically join into a single composite “super-resonance,” located at significantly lower frequencies than the plasmonic resonance. This super-resonance influences the optical properties in the low-frequency range, in particular, producing giant nonlinearities. We show that such nonlinearities can be used for efficient down-conversion from optical to terahertz and midinfrared frequencies on the submicrometer propagation distances in nanocomposites. We discuss the interaction of the quantum-confinement-induced super-resonance with the conventional plasmonic ones, as well as the unusual quantum level statistics, adapting here the paradigms of the quantum billiard theory and showing the possibility to control the resonance position and width using the geometry of the nanostructures.
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In this work, we consider the time-harmonic Maxwell's equations and their numerical solution with a domain decomposition method. As an innovative feature, we propose a feedforward neural ...network-enhanced approximation of the interface conditions between the subdomains. The advantage is that the interface condition can be updated without recomputing the Maxwell system at each step. The main part consists of a detailed description of the construction of the neural network for domain decomposition and the training process. To substantiate this proof of concept, we investigate a few subdomains in some numerical experiments with low frequencies. Therein the new approach is compared to a classical domain decomposition method. Moreover, we highlight current challenges of training and testing with different wave numbers and we provide information on the behaviour of the neural-network, such as convergence of the loss function, and different activation functions.
Efficient all-optical switching is a challenging task as photons are bosons and cannot immediately interact with each other. Consequently, one has to resort to nonlinear optical interactions, with ...the Kerr gate being the classical example. However, the latter requires strong pulses to switch weaker ones. Numerous approaches have been investigated to overcome the resulting lack of fan-out capability of all-optical switches, most of which relied on types of resonant enhancement of light-matter interaction. Here we experimentally demonstrate a novel approach that utilizes switching between different portions of soliton fission induced supercontinua, exploiting an optical event horizon. This concept enables a high switching efficiency and contrast in a dissipation free setting. Our approach enables fan-out, does not require critical biasing, and is at least partially cascadable. Controlling complex soliton dynamics paves the way towards building all-optical logic gates with advanced functionalities.Fan-out capability, permitting one photon to switch many others, is a crucial ingredient of practical all-optical switching schemes. Exploiting an optical event horizon, high contrast switching is experimentally and theoretically demonstrated with above-unity fan-out.
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