Clusters in Intense XUV pulses: effects of cluster size on expansion dynamics and ionization

We examine the effect of cluster size on the interaction of Ar$_{55}$-Ar$_{2057}$ with intense extreme ultraviolet (XUV) pulses, using a model we developed earlier that includes ionization via collisional excitation as an intermediate step. We find that the dynamics of these irradiated clusters is dominated by collisions. Larger clusters are more highly collisional, produce higher charge states, and do so more rapidly than smaller clusters. Higher charge states produced via collisions are found to reduce the overall photon absorption, since charge states of Ar$^{2+}$ and higher are no longer photo-accessible. We call this mechanism \textit{collisionally reduced photoabsorption}, and it decreases the effective cluster photoabsorption cross-section by more than 30% for Ar$_{55}$ and 45% Ar$_{2057}$. compared to gas targets with the same number of atoms. An investigation of the shell structure soon after the laser interaction shows an almost uniformly charged core with a modestly charged outer shell which evolves to a highly charged outer shell through collisions. This leads to the explosion of the outer positive shell and a slow expansion of the core, as was observed in mixed clusters at shorter wavelength [1]. The time evolution of the electron kinetic energy distribution begins as a (mostly) Maxwellian distribution. Larger clusters initially have higher temperature, but are overtaken by smaller temperature after the laser pulse. The electron velocity distribution of large clusters quickly become isotropic while smaller clusters retain the inherent anisotropy created by photoionization.Lastly, the total electron kinetic energy distribution is integrated over the spacial profile of the laser and the log-normal distribution of cluster size for comparison with a recent experiment [2], and good agreement is found.Comment: 13 pages, 11 figure

Improving On-Demand Single Photon Source Coherence and Indistinguishability Through a Time-Delayed Coherent Feedback

Single photon sources (SPSs) form an essential resource for many quantum information technologies. We demonstrate how the inclusion of coherent feedback in a scalable waveguide system, can significantly improves the two key figures of merit: coherence and indistinguishability. Our feedback protocol is simulated using a quantum trajectory discretized waveguide model which can be used to directly model Hanbury Brown and Twiss (HBT) and Hong-Ou-Mandel (HOM) interferometers. With the proper choice of the round trip phase, the non-Markovian dynamics from the time-delayed feedback enhances the spontaneous emission rate and improves the coherence and indistinguishability of the SPS by up to 56%. We also show how this mechanism suppresses the effects of unwanted dissipation channels such as off-chip decay and pure dephasing.Comment: 7 pages, 3 figure

Parallel FDTD modelling of nonlocality in plasmonics

As nanofabrication techniques become more precise, with ever smaller feature sizes, the ability to model nonlocal effects in plasmonics becomes increasingly important. While nonlocal models based on hydrodynamics have been implemented using various computational electromagnetics techniques, the finite-difference time-domain (FDTD) version has remained elusive. Here we present a comprehensive FDTD implementation of nonlocal hydrodynamics, including for parallel computing. As a sub-nanometer step size is required to resolve nonlocal effects, a parallel implementation makes the computational cost of nonlocal FDTD more affordable. We first validate our algorithms for small spherical metallic particles, and find that nonlocality smears out staircasing artifacts at metal surfaces, increasing the accuracy over local models. We find this also for a larger nanostructure with sharp extrusions. The large size of this simulation, where nonlocal effects are clearly present, highlights the importance and impact of a parallel implementation in FDTD. CCB

High harmonic generation in condensed and engineered materials:introduction

The emerging field of high harmonic generation in condensed matter systems lies at the confluence of strong-field physics, ultrafast optics, and nanotechnology and offers numerous avenues for fundamental research and applications. The goals of this JOSA B feature issue on high harmonic generation in condensed and engineered materials are to facilitate interaction between the different communities and to provide an up-to-date snapshot of the current status of this rapidly developing interdisciplinary field at the frontier of condensed materials and ultrafast physics.</p

On the performance of optical phased array technology for beam steering : effect of pixel limitations

Optical phased arrays are of strong interest for beam steering in telecom and LIDAR applications. A phased array ideally requires that the field produced by each element in the array (a pixel) is fully controllable in phase and amplitude (ideally constant). This is needed to realize a phase gradient along a direction in the array, and thus beam steering in that direction. In practice, grating lobes appear if the pixel size is not sub-wavelength, which is an issue for many optical technologies. Furthermore, the phase performance of an optical pixel may not span the required 2π phase range or may not produce a constant amplitude over its phase range. These limitations result in imperfections in the phase gradient, which in turn introduce undesirable secondary lobes. We discuss the effects of non-ideal pixels on beam formation, in a general and technology-agnostic manner. By examining the strength of secondary lobes with respect to the main lobe, we quantify beam steering quality and make recommendations on the pixel performance required for beam steering within prescribed specifications. By applying appropriate compensation strategies, we show that it is possible to realize high-quality beam steering even when the pixel performance is non-ideal, with intensity of the secondary lobes two orders of magnitude smaller than the main lobe. © 2020 OSA - The Optical Society. All rights reserved

Topographical coloured plasmonic coins

The use of metal nanostructures for colourization has attracted a great deal of interest with the recent developments in plasmonics. However, the current top-down colourization methods based on plasmonic concepts are tedious and time consuming, and thus unviable for large-scale industrial applications. Here we show a bottom-up approach where, upon picosecond laser exposure, a full colour palette independent of viewing angle can be created on noble metals. We show that colours are related to a single laser processing parameter, the total accumulated fluence, which makes this process suitable for high throughput industrial applications. Statistical image analyses of the laser irradiated surfaces reveal various distributions of nanoparticle sizes which control colour. Quantitative comparisons between experiments and large-scale finite-difference time-domain computations, demonstrate that colours are produced by selective absorption phenomena in heterogeneous nanoclusters. Plasmonic cluster resonances are thus found to play the key role in colour formation.Comment: 9 pages, 5 figure

Online Visualization of Operating Variables for Cars and Truck

Osazení sériově vyráběných automobilů elektronickými čidly řízenými centrální elektronickou jednotkou je dlouholetý standart. Po boku standartní produkce také vždy existoval menší proud alternativních projektů automobilů na zakázku, prototypů, domácích pokusů a studentských prací, či terénních, historických nebo jakýmkoliv způsobem nestandartních vozidel. Tato práce nachází inspiraci v modelu sériové výroby, ale zaměřuje se a hledá řešení právě pro menší alternativní projekty. Snaží se přijít s kompaktním řešením, které by bylo zjednodušenou, levnější a dostupnější verzí standartních elektronických modulů. Dále se zaměří na možnosti přenosu, analýzy a zobrazení dat takto získaných v navržené webové aplikaci pro mobilní a desktopová zařízení.The placement of an electronic sensors controlled with an electronic central unit into automobiles of the standard production has been common for many years. Also there have been existing always a smaller number of an alternative projects of a custom automobiles, a prototypes, a home DIY tryouts and student’s works, or an offroad, historical or any type of a non-standard vehicles on the side of the standard production. This thesis gets an inspiration in the model of the standard production, but at the same time will search and focus on an alternative solution for the projects of a smaller scale. The thesis will try to bring a compact resolution, which shall be simplified, more affordable and better available version of the standard electronic modules. Furthermore, the thesis will focus on the possibilities of a transfer, an analysis and a visualization of the data received, in the introduced web application for a mobile and desktop devices.460 - Katedra informatikyvýborn

Augmented collisional ionization via excited states in XUV cluster interactions

The impact of atomic excited states is investigated via a detailed model of laser-cluster interactions, which is applied to rare gas clusters in intense femtosecond pulses in the extreme ultraviolet (XUV). This demonstrates the potential for a two-step ionization process in laser-cluster interactions, with the resulting intermediate excited states allowing for the creation of high charge states and the rapid dissemination of laser pulse energy. The consequences of this excitation mechanism are demonstrated through simulations of recent experiments in argon clusters interacting with XUV radiation, in which this two-step process is shown to play a primary role; this is consistent with our hypothesis that XUV-cluster interactions provide a unique window into the role of excited atomic states due to the relative lack of photoionization and laser field-driven phenomena. Our analysis suggests that atomic excited states may play an important role in interactions of intense radiation with materials in a variety of wavelength regimes, including potential implications for proposed studies of single molecule imaging with intense X-rays.Comment: 4 pages, 2 figure