Quasicrystals are aperiodic structures with rotational symmetries forbidden to conventional periodic crystals; examples of quasicrystals can be found in aluminum alloys, polymers, and even ancient Islamic art. Here, we present direct experimental observation of disorder-enhanced wave transport in quasicrystals, which contrasts directly with the characteristic suppression of transport by disorder. Our experiments are carried out in photonic quasicrystals, where we find that increasing disorder leads to enhanced expansion of the beam propagating through the medium. By further increasing the disorder, we observe that the beam progresses through a regime of diffusive-like transport until it finally transitions to Anderson localization and the suppression of transport. We study this fundamental phenomenon and elucidate its origins by relating it to the basic properties of quasicrystalline media in the presence of disorder.
We discover long-lived (microsecond-scale) optical waveguiding in the wake of atmospheric laser filaments. We also observe the formation and then outward propagation of the consequent sound wave. These effects may be used for remote induction of atmospheric long-lived optical structures from afar which could serve for a variety of applications.* These authors contributed equally to this work. 2Propagation of self-guided laser filaments through air and other gases results in a rich variety of phenomena and applications [1][2][3]. A laser filament is formed when a femtosecond pulse, with peak intensity above the critical power for collapse (3 GW in air at an optical wavelength of 800 nm), is propagating in a transparent medium [1]. In air, the diameter of a filament is approximately 100 μm and it can propagate over distances much longer than the Rayleigh length, from 10 cm up to the kilo-meter range [4][5][6][7]. A filament is formed due to a dynamic balance between the linear diffractive and dispersive properties of the medium and its nonlinear features such as self-focusing optical Kerr effect and defocusing due to the free electrons which are released from molecules through multi-photon ionization. In the atmosphere, filaments can be initiated at predefined remote distances [4,5] and propagate through fog, clouds and turbulence [8,9]. Thus, filaments are attractive for atmospheric applications such as remote spectroscopy This mechanism was used for guiding properly delayed picosecond pulses [21,22], but at times larger than several nanosecond after the filamenting pulse, even this process does not leave behind any waveguiding effects. In fact, all processes resulting from plasma or molecular alignment in the wake of atmospheric laser filaments are limited to the first few nanoseconds period. Consequently, it was generally believed that ten nanoseconds after the filament, the medium does not exhibit any waveguiding effect. In contrast to that, it was recently discovered that 0.1-1 milliseconds after the filament, there is a circular negative index change that acts as an antiguide by defocusing a probe beam [23]. This effect was attributed to reduction in the air density at the center of the filament 4 as a result of heating. Altogether, to the best of our knowledge, thus far all experiments and theories on laser filamentation in the atmosphere concluded that there is no longlived (>10 nanosecond) waveguiding effect left behind the femtosecond filamenting pulse. This severely limits any CW application of laser filamentation, because the repetition rate of any high power laser used for creating the filament is low, hence for most of the time between pulses light would not be guided. Likewise, any other potential application would have to "live" on a picosecond scale, because at later times, waveguiding by the filament was thought to be nonexistent.Here, we show the exact opposite: we demonstrate theoretically and experimentally that the filament induces a transient positive index change which lasts for approximate...
We discuss the dynamics of particles in one dimension in potentials that are random in both space and time. The results are applied to recent optics experiments on Anderson localization, in which the transverse spreading of a beam is suppressed by random fluctuations in the refractive index. If the refractive index fluctuates along the direction of the paraxial propagation of the beam, the localization is destroyed. We analyze this broken localization in terms of the spectral decomposition of the potential. When the potential has a discrete spectrum, the spread is controlled by the overlap of Chirikov resonances in phase space. As the number of Fourier components is increased, the resonances merge into a continuum, which is described by a Fokker-Planck equation. We express the diffusion coefficient in terms of the spectral intensity of the potential. For a general class of potentials that are commonly used in optics, the solutions to the Fokker-Planck equation exhibit anomalous diffusion in phase space, implying that when Anderson localization is broken by temporal fluctuations of the potential, the result is transport at a rate similar to a ballistic one or even faster. For a class of potentials which arise in some existing realizations of Anderson localization, atypical behavior is found.
We study the long-range propagation of incoherent light following the modulation instability (MI) process in non-instantaneous nonlinear Kerr-type media. We find that the system eventually reaches a steady-state characterized by a lower degree of coherence than in the initial state, with small fluctuations around a pronounced mean value. We find that the average values of the spatial correlation distance at steady-state and the fluctuations around it, which are obtained either through ensemble averaging, or by spatial averaging, or via temporal averaging, are all identical. This feature may be viewed as indication of ergodic behavior, which occurs in the long-time evolution following incoherent MI. Finally, we find that the steady-state properties of the system depend on the initial coherence but not on the nonlinearity strength, although the system evolves faster to steady-state as the strength of the nonlinearity is increased.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.