Optimization of multi-color laser waveform for high-order harmonic generation

With the development of laser technologies,multi-color light-field synthesis with complete amplitude and phase control would make it possible to generate arbitrary optical waveforms.A practical optimization algorithm is needed to generate such a waveform in order to control strong-field processes.We review some recent theoretical works of the optimization of amplitudes and phases of multi-color lasers to modify the single-atom high-order harmonic generation based on genetic algorithm.By choosing different fitness criteria,we demonstrate that：（i） harmonic yields can be enhanced by 10 to 100 times,（ii） harmonic cutoff energy can be substantially extended,（iii） specific harmonic orders can be selectively enhanced,and（iv） single attosecond pulses can be efficiently generated.The possibility of optimizing macroscopic conditions for the improved phase matching and low divergence of high harmonics is also discussed.The waveform control and optimization are expected to be new drivers for the next wave of breakthrough in the strong-field physics in the coming years.

Intelligent optimization methods of phase-modulation waveform

With the continuous improvement of radar intelligence, it is difficult for traditional countermeasures to achieve ideal results. In order to deal with complex, changeable, and unknown threat signals in the complex electromagnetic environment, a waveform intelligent optimization model based on intelligent optimization algorithm is proposed. By virtue of the universality and fast running speed of the intelligent optimization algorithm, the model can optimize the parameters used to synthesize the countermeasure waveform according to different external signals, so as to improve the countermeasure performance.Genetic algorithm(GA) and particle swarm optimization(PSO)are used to simulate the intelligent optimization of interruptedsampling and phase-modulation repeater waveform. The experimental results under different radar signal conditions show that the scheme is feasible. The performance comparison between the algorithms and some problems in the experimental results also provide a certain reference for the follow-up work.

Effects of the actuation waveform on the drop size reduction in drop-on-demand inkjet printing

In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations.Two different types of waveforms,namely the unipolar and bipolar actuations,are investigated for three fluids with different physical properties.We focus on two key parameters,which are the dwell time and the velocity amplitude.For the unipolar driving,the ejection velocity and the ejected liquid volume are both increased as the velocity amplitude becomes larger.The dwell time only has minor effects on both the ejection velocity and the ejected liquid volume.The ejection velocity decreases significantly for large liquid viscosity,while the influences of viscosity on the ejected liquid volume are much weaker.Four different droplet morphologies and the corresponding parameter ranges are identified.The droplet radius can be successfully reduced to about 40%e of the nozzle exit radius.For the bipolar waveforms,same droplet morphologies are observed but with shifted boundaries in the phase space.The minimal radius of stable droplet produced by the bipolar waveforms is even smaller compared to the unipolar ones.

Operator Splitting and Local Time-Stepping Methods for Transport Problems in Fractured Porous Media

This paper is concerned with efficient numerical methods for the advectiondiffusion equation in a heterogeneous porous medium containing fractures.A dimensionally reduced fracture model is considered,in which the fracture is represented as an interface between subdomains and is assumed to have larger permeability than the surrounding area.We develop three global-in-time domain decomposition methods coupled with operator splitting for the reduced fracture model,where the advection and the diffusion are treated separately by different numerical schemes and with different time steps.Importantly,smaller time steps can be used in the fracture-interface than in the subdomains.The first two methods are based on the physical transmission conditions,while the third one is based on the optimized Schwarz waveform relaxation approach with Ventcel-Robin transmission conditions.A discrete space-time interface system is formulated for each method and is solved iteratively and globally in time.Numerical results for two-dimensional problems with various P′eclet numbers and different types of fracture are presented to illustrate and compare the convergence and accuracy in time of the proposed methods with local time stepping.