Stability Control Method of Hybrid Impulsive System Based on M-Matrix

Aiming at the problems of poor control effect and poor stability of the mixed pulse system with the traditional method, this paper introduces the M-matrix to establish the pulse delay differential indefinite formula and realize stability control of the mixed pulse system. The synchronization problem of mixed-pulse systems in complex networks is analyzed using M matrix. The local coupling strength of the impulsive system is controlled according to the adaptive method. A class of Multi-Lyapunov functions is constructed for stability control of hybrid impulsive systems. The proposed method is proved to have better control effect through experiments.

Quantifying the impact of temporal analysis of products reactor initial state uncertainties on kinetic parameters

The temporal analysis of products (TAP) reactor provides a route to extract intrinsic kinetics from transient measurements. Current TAP uncertainty quantification only considers the experimental noise present in the outlet flow signal. Additional sources of uncertainty such as initial surface coverages, catalyst zone location, inert void fraction, gas pulse intensity and pulse delay, are not included. For this reason, a framework for quantifying initial state uncertainties present in TAP experiments is presented and applied to a carbon monoxide oxidation case study. Two methods for quantifying these sources of uncertainty are introduced. The first utilizes initial state sensitivities to approximate the parameter variances and provide insights into the structural certainty of the model. The second generates parameter confidence distributions through an ensemble-based sampling algorithm. The initial state covariance matrix can ultimately be merged with the experimental noise covariance matrix, providing a unified description of the parameter uncertainties for a TAP experiment.

Effect of longitudinal epsilon-near-zero regime in dynamics of ultrashort laser pulses in hyperbolic metamaterials

Optical properties of hyperbolic metamaterials (HMMs) are in stark contrast to properties of ordinary media that fuels interest to various applications of HMMs in photonics. Special attention is attributed to the epsilon-near zero regime (ENZ) of HMMs that is the spectral point in which real part of the permittivity of the HMM becomes zero. This is accompanied by the effects of field enhancement having far-reaching applications. Here we focus on the experimental and theoretical investigation of the propagation of an ultrashort laser pulse through the silver nanorod-based HMM slab in the spectral range over the ENZ. We revealed pronounced resonant change of the pulse delay in HMMs and the transition between the superluminal and slow pulse propagation at the ENZ spectral point. Observed dynamical phenomena are confirmed theoretically and attributed to unusual case when the spectral half of an ultrashort pulse has elliptical dispersion and another has the hyperbolic one. Special attention is payed to the propagation of chirped laser pulses in the HMMs.

Microwave realization of multiresonant metasurfaces for achromatic pulse delay

We propose a microwave realization of a metasurface that can delay broadband pulses without distortion in reflection. In order to obtain large and broadband pulse delay, we harness the synergetic phase delay of five sharply-resonant meta-atoms. More specifically, three electric-LC and two split ring resonators, supporting electric and magnetic dipole resonances, respectively, are combined in a subwavelength unit cell. The resonances are spectrally interleaved and specifically designed to provide a spectrally-constant reflection amplitude and group delay according to the prescription in [ACS Photonics 5, 1101, 2018]. The designed metasurface is electrically ultrathin (λ0/19), since it relies on resonant phase delay exclusively, instead of phase accumulation via propagation. We show delay of 700-MHz Gaussian pulses centred at 11 GHz by 1.9 ns, corresponding to approximately 21 carrier cycles. Our results highlight the practical potential of metasurfaces for broadband dispersion control applications.

Throughput Improvement in Femtosecond Laser Ablation of Nickel by Double Pulses

In this study, femtosecond laser double pulses were tested to improve their nickel ablation efficiency. The experimental results indicated that compared with single pulses, double pulses with different delay times generated craters with larger diameters and depths. The results obtained for three sets of double pulses with different energy ratios indicated that double pulses with an energy ratio of 1:9 had the highest ablation efficiency, followed by those with energy ratios of 2:8 and 5:5. The double pulses with the aforementioned three energy ratios achieved the maximum ablation efficiency when the delay time was 3–4 ps. Compared with single pulses, double pulses with an energy ratio of 1:9 generated craters with an up to 34% greater depth and up to 14% larger diameter. In addition, an interference effect was observed with a double pulse delay time of 0 ps, which has seldom been reported in the literature. The double pulses were simulated using the two-temperature model. The simulation results indicated that double pulses with an energy ratio of 1:9 with a delay time of 4 ps can perform the strongest ablation. These simulation results are in line with the experimental results.

Time-resolved relaxation and fragmentation of polycyclic aromatic hydrocarbons investigated in the ultrafast XUV-IR regime

Polycyclic aromatic hydrocarbons (PAHs) play an important role in interstellar chemistry and are subject to high energy photons that can induce excitation, ionization, and fragmentation. Previous studies have demonstrated electronic relaxation of parent PAH monocations over 10–100 femtoseconds as a result of beyond-Born-Oppenheimer coupling between the electronic and nuclear dynamics. Here, we investigate three PAH molecules: fluorene, phenanthrene, and pyrene, using ultrafast XUV and IR laser pulses. Simultaneous measurements of the ion yields, ion momenta, and electron momenta as a function of laser pulse delay allow a detailed insight into the various molecular processes. We report relaxation times for the electronically excited PAH*, PAH+* and PAH2+* states, and show the time-dependent conversion between fragmentation pathways. Additionally, using recoil-frame covariance analysis between ion images, we demonstrate that the dissociation of the PAH2+ ions favors reaction pathways involving two-body breakup and/or loss of neutral fragments totaling an even number of carbon atoms.

Distinguishing Resonant from Non-Resonant Nonlinear Optical Processes Using Intensity–Intensity Correlation Analyses

Three-color coherent anti-Stokes Raman scattering (CARS) represents non-degenerate four wave mixing that includes both non-resonant and resonant processes, the contributions of which depend upon how the molecular vibrational modes are being excited by the input laser pulses. The scattering signal due to resonant processes builds up progressively. An advanced analytical tool to reveal this deferred resonant signal buildup phenomenon is in need. In this work, we adapt a quantitative analytical tool by introducing one-dimensional and two-dimensional intensity–intensity correlation functions in terms of a new variable (probe pulse delay) and a new perturbation parameter (probe pulse linewidth). In particular, discrete diagonal directional sums are defined here as a tool to reduce both synchronous and asynchronous two-dimensional correlation spectroscopy (2D-COS) maps down to one-dimensional plots while maintaining the valuable analytical information. Detailed analyses using the all-Gaussian coherent Raman scattering closed-form solutions and the representative experimental data for resonant and non-resonant processes are presented and compared. The present work holds a promising potential for industrial application, e.g., by extractive industries to distinguish hydrocarbons (chemically resonant substance) from water (non-resonant contaminant) by utilizing the one- and two-dimensional correlation analyses.

Electric Field Assisted Femtosecond Laser Preparation of Au@TiO2 Composites with Controlled Morphology and Crystallinity for Photocatalytic Degradation

TiO2 is popular in photocatalytic degradation dye pollutants due to its abundance and its stability under photochemical conditions. Au loaded TiO2 can achieve efficient absorption of visible light and deal with the problem of low conversion efficiency for solar energy of TiO2. This work presents a new strategy to prepare Au nanoparticles-loaded TiO2 composites through electric−field−assisted temporally−shaped femtosecond laser liquid-phase ablation of Au3+ and amorphous TiO2. By adjusting the laser pulse delay and electric field parameters, gold nanoparticles with different structures can be obtained, such as nanospheres, nanoclusters, and nanostars (AuNSs). AuNSs can promote the local crystallization of amorphous TiO2 in the preparation process and higher free electron density can also be excited to work together with the mixed crystalline phase, hindering the recombination between carriers and holes to achieve efficient photocatalytic degradation. The methylene blue can be effectively degraded by 86% within 30 min, and much higher than the 10% of Au nanoparticles loaded amorphous TiO2. Moreover, the present study reveals the crystallization process and control methods for preparing nanoparticles by laser liquid ablation, providing a green and effective new method for the preparation of high-efficiency photocatalytic materials.