Simulations On The Single Attosecond Pulse Generation From Macroscopic High-order Harmonics By Optimized Multicolor Laser Field

The attosecond(as)pulses are important tools to observe and control the ultrafast electron dynamics in atoms,molecules and solids.At present,single attosecond pulse with width of about 50 as can be generated from high-order harmonics only in few laboratories in the world,while the relevant domestic record is 88 as.Obtaining shorter attosecond pulses is still very necessary and important for strong-field physics and attosecond science.Combining the current laser technology and experimental conditions,this paper has carried out theoretical simulations on how to use the multi-color combined laser field to generate ultra-short isolated attosecond pulses(IAP).The main results and conclusions are as follows:Taking the 800 nm multi-cycle laser pulse as the fundamental field,we use the genetic algorithm to optimize the waveforms of two-color and three-color laser pulses,and the sub-cycle laser pulses are obtained.High-order harmonic spectrum with wideband supercontinuum can be generated with optimized laser pulse interacting with neon atom.When only the response of single atom is considered,our simulations show that about 50 as and 40 as IAP with central energy of about 200 eV can be obtained by superimposing appropriate harmonics generated by optimized two-and three-color laser pulses,respectively.More importantly,after considering the propagation effects,about50 as IAPs are obtained with spatial filtering of harmonics in the far field,under reasonable experimental parameters(gas pressure,nozzle length and position).With great advent of the ultra-fast lasers technology,such as coherent waveform synthesizing and optical parametric chirped-pulse amplification,this work gives helpful theoretical guidance for ultra-short IAP generation in the experiment.