Self-guided Propagation Research Articles

Two-step graph propagation for incomplete multi-view clustering

Incomplete multi-view clustering addresses scenarios where data completeness cannot be guaranteed, diverging from traditional methods that assume fully observed features. Existing approaches often overlook high-order correlations present in multiple similarity graphs, and suffer from inefficiencies due to iterative optimization procedures. To overcome these limitations, we propose a graph-based model leveraging graph propagation to effectively handle incomplete data. The proposed method translates incomplete instances into incomplete graphs, and infers missing entries through a graph propagation strategy, ensuring the inferred data is meaningful and contextually relevant. Specifically, a self-guided graph is constructed to capture global relationships, while partial graphs represent view-specific similarities. The self-guided graph is first completed through self-guided graph propagation, which subsequently aids in the propagation of the partial graphs. The key contribution of graph propagation is to propagate information from complete data to incomplete data. Furthermore, the high-order correlation across multiple views is captured by low-rank tensor learning. To enhance computational efficiency, the optimization procedure is decoupled and implemented in a stepwise manner, eliminating the need for iterative updates. Extensive experiments validate the robustness of the proposed method, demonstrating superior performance compared to state-of-the-art methods, even when all instances are incomplete.

Self-Guided Partial Graph Propagation for Incomplete Multiview Clustering.

In this work, we study a more realistic challenging scenario in multiview clustering (MVC), referred to as incomplete MVC (IMVC) where some instances in certain views are missing. The key to IMVC is how to adequately exploit complementary and consistency information under the incompleteness of data. However, most existing methods address the incompleteness problem at the instance level and they require sufficient information to perform data recovery. In this work, we develop a new approach to facilitate IMVC based on the graph propagation perspective. Specifically, a partial graph is used to describe the similarity of samples for incomplete views, such that the issue of missing instances can be translated into the missing entries of the partial graph. In this way, a common graph can be adaptively learned to self-guide the propagation process by exploiting the consistency information, and the propagated graph of each view is in turn used to refine the common self-guided graph in an iterative manner. Thus, the associated missing entries can be inferred through graph propagation by exploiting the consistency information across all views. On the other hand, existing approaches focus on the consistency structure only, and the complementary information has not been sufficiently exploited due to the data incompleteness issue. By contrast, under the proposed graph propagation framework, an exclusive regularization term can be naturally adopted to exploit the complementary information in our method. Extensive experiments demonstrate the effectiveness of the proposed method in comparison with state-of-the-art methods. The source code of our method is available at the https://github.com/CLiu272/TNNLS-PGP.

Self-Guidance and Self-Focusing of Rippled Electromagnetic Radiation Pulse in High Density Magnetoactive Plasma


 Inside the plasma, when an intense rippled electromagnetic radiation pulse experiences self-focusing, one need to taking account of radial expansion in view of charge displacement due to ponderomotive force on electron and variation in the mass of oscillating electron under the influence of relativistic effect due to electromagnetic field. The extraordinary-mode (E-mode) propagation in a magnetoactive plasma, with stationary magnetic field, which is analogous to the wavering magnetic field of the electromagnetic radiation pulse, is the key feature for the self-guided propagation of rippling electromagnetic radiation pulse in magnetoactive plasma. If the condition for ultra-fast volume ionization is achieved, the radiation pulse itself can generate such a stationary magnetic field. It is demonstrated that external magnetic field affects the channels, causing them to bend. These effects cast new light on the phenomena of self-focusing of rippled electromagnetic radiation pulse. They raise the possibility of combining energy from several channels into one. It is found that the magnetic field strongly influences the plasma dynamic behavior and overall propagation of rippled electromagnetic radiation pulse.
 Keywords: Self-focusing, Self-guidance, Magnetized-plasma, Beam-propagation, Nonlinearity

Mutually guided light and particle beam propagation

The polarizability of atoms and molecules gives rise to optical forces that trap particles and a refractive index that guides light beams, potentially leading to a self-guided laser and particle beam propagation. In this paper, the mutual interactions between an expanding particle beam and a diffracting light beam are investigated using an axisymmetric particle-light coupled simulation. The nonlinear coupling between particles and photons is dependent on the particle beam radius, particle density, particle velocity and temperature, polarizability, light beam waist, light frequency (with respect to the resonance frequency), and light intensity. The computational results show that the maximum propagation distance is achieved when the waveguiding effect is optimized to single-mode operation. The application of the coupled beam propagation as a space propulsion system is discussed.

Self-Guided Belief Propagation - A Homotopy Continuation Method.

Belief propagation (BP) is a popular method for performing probabilistic inference on graphical models. In this work, we enhance BP and propose self-guided belief propagation (SBP) that incorporates the pairwise potentials only gradually. This homotopy continuation method converges to a unique solution and increases the accuracy without increasing the computational burden. We provide a formal analysis to demonstrate that SBP finds the global optimum of the Bethe approximation for attractive models where all variables favor the same state. Moreover, we apply SBP to various graphs with random potentials and empirically show that: (i) SBP is superior in terms of accuracy whenever BP converges, and (ii) SBP obtains a unique, stable, and accurate solution whenever BP does not converge.

Self-Guiding of Long-Wave Infrared Laser Pulses Mediated by Avalanche Ionization.

Nonlinear self-guided propagation of intense long-wave infrared (LWIR) laser pulses is of significant recent interest, as it promises high power transmission without beam breakup and multifilamentation. Central to self-guiding is the mechanism for the arrest of self-focusing collapse. Here, we show that discrete avalanche sites centered on submicron aerosols can arrest self-focusing, providing a new mechanism for self-guided propagation of moderate intensity LWIR pulses in outdoor environments. Our conclusions are supported by simulations of LWIR pulse propagation using an effective index approach that incorporates the time-resolved plasma dynamics of discrete avalanche breakdown sites.

Self-channelled high harmonic generation of water window soft x-rays

Owing to the increasing significance of high harmonic generation (HHG) as a tabletop coherent x-ray source and the coming of age of intense infrared (IR) lasers, the development of high brightness soft x-ray beamlines is gaining a lot of attention. We discuss the self-guided propagation of high energy IR pulses around 1.8 μm centre wavelength being loosely focused into a long, high-pressure gas cell. A bright x-ray beam with photon energies extending up to the oxygen K-edge at 543 eV is achieved with a flux of 2.9 × 103 photons/shot/1% bandwidth around the carbon K-edge (280 eV). We provide experimental and numerical evidence of an ionization steady state condition in the generation medium causing self-channelling and intensity clamping of the driving field. While the later limits the HHG cut-off energy for a given driving field wavelength, self-channelling increases the HHG flux through a longer, phase-matched, interaction length and provides a well-collimated HHG beam covering more than three octaves from <50 to 550 eV.

Measurements of self-guiding of ultrashort laser pulses over long distances

We report on the evaluation of the performance of self-guiding over extended distances with and focussing geometries. Guiding over or more than 100 Rayleigh ranges was observed with the optic at . Analysis of guiding performance found that the extent of the exiting laser spatial mode closely followed the matched spot size predicted by 3D nonlinear theory. Self-guiding with an optic was also characterised, with guided modes observed for a plasma length of and a plasma density of . This corresponds to self-guided propagation over 53 Rayleigh ranges and is similar to distances obtained with discharge plasma channel guiding.

Nonlinear modes of an intense laser beam interacting with a periodic lattice of nanoparticle

Self-guided nonlinear propagation of an intense laser beam through a periodic lattice of nanoparticle is studied. Using a perturbative method, a cubic nonlinear wave equation describing the laser-nanoparticle interaction in the weakly relativistic regime is derived. Transverse Eigen modes of the laser, nonlinear dispersion relation and its related group velocity are obtained. It is shown that the best fitted function to the transverse profile is Gaussian. Effect of the laser amplitude and also the ratio of nanoparticles radius to their separation on the nonlinear dispersion and amplitude profiles are investigated. It is found that the increase in the just mentioned parameters leads to the localization of transverse profile around the propagation axis.

Nonlinear dispersion and transverse profile of intense electromagnetic waves, propagating through electron-positron-ion hot magnetoplasma

Self-guided nonlinear propagation of intense circularly-polarized electromagnetic waves in a hot electron-positron-ion magnetoplasma is studied. Using a relativistic fluid model, a nonlinear equation is derived, which describes the interaction of the electromagnetic wave with the plasma in the quasi-neutral approximation. Transverse Eigen modes, the nonlinear dispersion relation and the group velocity are obtained. Results show that the transverse profile in the case of magnetized plasma with cylindrical symmetry has a radially damping oscillatory form. Effect of applying external magnetic fields, existence of the electron-positron pairs, changing the amplitude of the electromagnetic wave, and its polarization on the nonlinear dispersion relation and Eigen modes are studied.

Upper-limit power for self-guided propagation of intense lasers in underdense plasma – CORRIGENDUM

Upper-limit power for self-guided propagation of intense lasers in underdense plasma – CORRIGENDUM

Upper-limit power for self-guided propagation of intense lasers in underdense plasma

AbstractIt is found that there is an upper-limit critical power for self-guided propagation of intense lasers in plasma in addition to the well-known lower-limit critical power set by the relativistic effect. Above this upper-limit critical power, the laser pulse experiences defocusing due to expulsion of local plasma electrons by the transverse ponderomotive force. Associated with the upper-limit power, a lower-limit critical plasma density is also found for a given laser spot size, below which self-focusing does not occur for any laser power. Both the upper-limit power and the lower-limit density are derived theoretically and verified by two-dimensional particle-in-cell simulations. The present study provides new guidance for experimental designs, where self-guided propagation of lasers is essential.

Supra-thermal electron beam stopping power and guiding in dense plasmas

AbstractFast-electron beam stopping mechanisms in media ranging from solid to warm dense matter have been investigated experimentally and numerically. Laser-driven fast electrons have been transported through solid Al targets and shock-compressed Al and plastic foam targets. Their propagation has been diagnosed via rear-side optical self-emission and Kα X-rays from tracer layers. Comparison between measurements and simulations shows that the transition from collision-dominated to resistive field-dominated energy loss occurs for a fast-electron current density ~5 × 1011 A cm−2. The respective increases in the stopping power with target density and resistivity have been detected in each regime. Self-guided propagation over 200μm has been observed in radially compressed targets due to ~1kT magnetic fields generated by resistivity gradients at the converging shock front.

Self-guided propagation of ultrashort laser pulses in the anomalous dispersion region of transparent solids: a new regime of filamentation.

We report measurements concerning the propagation of femtosecond laser pulses in fused silica with a wavelength at 1.9 μm falling in the negative group velocity dispersion region. Under sub-GW excitation power, stable filaments are observed over several cm showing the emergence of nonspreading pulses both in space and time. At higher excitation powers, one observes first multiple pulse splitting followed by the emergence of the quasispatiotemporal solitary filament. These results are well reproduced by numerical simulations.

Upper limit power for self-guided propagation of intense lasers in plasma

It is shown that there is an upper-limit laser power for self-focusing of a laser pulse in plasma in addition to the well-known lower-limit critical power set by the relativistic effect. This upper limit is caused by the transverse ponderomotive force of the laser, which tends to expel plasma electrons from the laser propagating area. Furthermore, there is a lower-limit plasma density for a given laser spot size, below which self-focusing does not occur for any laser power. Both the lower-limit density and the upper-limit power are derived theoretically and verified by two-dimensional and three-dimensional particle-in-cell simulations. It is also found that plasma channels may be unfavorable for stable guiding of lasers above the upper-limit power.

Vectorial self-diffraction effect in optically Kerr medium

We investigate the far-field vectorial self-diffraction behavior of a cylindrical vector field passing though an optically thin Kerr medium. Theoretically, we obtain the analytical expression of the focal field of the cylindrical vector field with arbitrary integer topological charge based on the Fourier transform under the weak-focusing condition. Considering the additional nonlinear phase shift photoinduced by a self-focusing medium, we simulate the far-field vectorial self-diffraction patterns of the cylindrical vector field using the Huygens-Fresnel diffraction integral method. Experimentally, we observe the vectorial self-diffraction rings of the femtosecond-pulsed radially polarized field and high-order cylindrical vector field in carbon disulfide, which is in good agreement with the theoretical simulations. Our results benefit the understanding of the related spatial self-phase modulation effects of the vector light fields, such as spatial solitons, self-trapping, and self-guided propagation.

Self-Guided Laser Wakefield Acceleration beyond 1 GeV Using Ionization-Induced Injection

The concepts of matched-beam, self-guided laser propagation and ionization-induced injection have been combined to accelerate electrons up to 1.45 GeV energy in a laser wakefield accelerator. From the spatial and spectral content of the laser light exiting the plasma, we infer that the 60 fs, 110 TW laser pulse is guided and excites a wake over the entire 1.3 cm length of the gas cell at densities below 1.5 × 10(18) cm(-3). High-energy electrons are observed only when small (3%) amounts of CO2 gas are added to the He gas. Computer simulations confirm that it is the K-shell electrons of oxygen that are ionized and injected into the wake and accelerated to beyond 1 GeV energy.

K-shell x-ray emission enhancement via self-guided propagation of intense laser pulses in Ar clusters

K-shell x-ray at about 3 keV emitted from Ar clusters irradiated by 110 mJ 55 fs intense laser pulses is studied. The x-ray flux is optimized by moving the nozzle away from the focus of the laser pulse. The total flux of K-shell x-ray photons in 4pi reaches a maximum of 4.5x10(9) photons/shot with a conversion efficiency of 2.5x10(-5) when the nozzle displacement is 2 mm and a long plasma channel is observed by a probe beam.

Generation of long plasma channels in air by focusing ultrashort laser pulses with an axicon

We show that by focusing ultrashort-pulsed laser beams in air with an axicon, relatively long plasma channels can be generated. The axicon generates Bessel-like beams, where the on-axis intensity stays high over distances much longer compared to focusing with conventional lenses. We developed a scheme to detect the presence of the plasma, based on its screening property. Using this scheme, we detected plasma channels longer than 1 m and 3.5 m generated by 8 mJ and 90 mJ input pulse energies, respectively. Our simulations show that axicon focusing can yield self-guided propagation with or without contribution of plasma, depending on the input pulse power.

Oval-like hollow intensity distribution of tightly focused femtosecond laser pulses in air

The propagation of a tightly focused femtosecond laser pulse in air has been investigated. Unlike long-distance self-guided propagation of short laser pulses, a novel oval-like hollow distribution of the laser intensity is observed in the experiments and reproduced by the numerical simulations. The formation of the hollow structures can be explained by the interplay between ionization-induced refraction and Kerr self-focusing.