利用三色组合脉冲激光获得孤立阿秒脉冲发射

孤立阿秒脉冲因可以跟踪和控制原子及分子内电子的运动过程而备受关注.本文从理论上开展了氦原子在3束飞秒脉冲激光组合场辐照下产生的高次谐波和阿秒脉冲辐射的研究.组合激光场由16 fs/1600 nm,15 fs/1100 nm和5.3 fs/800 nm的钛宝石脉冲构成.与前两束脉冲合成的双色场产生谐波谱相比,附加钛宝石脉冲的三色场产生的高次谐波发射谱呈现出高转换效率及宽带超连续特性,超连续谱范围覆盖从230—690次谐波,傅里叶变换后实现了128 as高强度孤立短脉冲的产生.该结果归因于合成的三色场呈现出高功率及少周期的中红外飞秒脉冲激光特性,可以有效控制原子电离以及复合发生在中红外飞秒脉冲的一个有效光学周期内.

Isolated attosecond pulse generation from helium atom irradiated by a three-color laser pulse

Isolated attosecond pulses enables the studying and controlling of ultrafast electron processes in atoms and molecules.High-order harmonic generation(HHG)is the most promising way to generate such pulses,benefiting from the broad plateau structure of the typical HHG spectrum.We theoretically investigate high-order harmonic and attosecond pulse generation from helium atom in a three-color laser field,which is synthesized by 16 fs/1600 nm,15 fs/1100 nm and 5 fs/800 nm pulse laser.Compared with harmonic spectrum generated by a two-color laser field synthesized by 16 fs/1600 nm and 15 fs/1100 nm,the harmonic spectrum generated from the synthesized three-color field exhibits high conversion efficiency and broadband supercontinuum characteristics.The continuous spectrum range covers from 230th to 690th harmonics,and the generation of 128 attosecond isolated short pulses with higher intensity is realized after Fourier transform.This result is attributable to the fact that the synthesized three-color electric field exhibits high-intensity and few-cycle midinfrared femtosecond pulse laser characteristics,which can effectively control atomic ionization and recombination occurring within an effective optical period of the mid-infrared femtosecond pulse.This scheme solves the problems faced by the current femtosecond pulse laser technology,i.e.the few-cycle mid-infrared femtosecond pulse laser cannot have both carrier envelope phase stability and high power output.