Non-perturbative QED Model with Dressed States to Tackle HHG in Ultrashort Intense Laser Pulses

Classical effect for enhanced high harmonic yield in ultrashort laser pulses with a moderate laser intensity

We study the influence of the pulse duration on high harmonic generation (HHG) with exploring a wide laser-parameter region theoretically. Previous studies have showed that for high laser intensities near to the saturation ionization intensity, the HHG inversion efficiency is higher for shorter pulses since the ground-state depletion is weaker in the latter. Surprisingly, our simulations show this high efficiency also appears even for a moderate laser intensity at which the ionization is not strong. A classical effect relating to shorter travel distances of the rescattering electron in shorter…

High harmonic generation from pre-ionized H$_2$ in ultrashort intense laser fields

Effects of the laser pulse wavelength and intensity on the HHG production from the \textit{ionic} and \textit{homolytic} pre-ionization transient states of the two-electron H$_{2}$ system exposed to ultrashort intense laser pulses are studied by solving time-dependent Schrödinger equation. It is found that for the populated homolytic species in each half cycle of the laser pulse having enough strength, a pair of strong and weak HHG radiations are produced simultaneously. For the populated ionic species divided into two regions, in each half cycle, one of the ionic regions has a strong radiatio…

Pulse-duration dependence of high-order harmonic generation with coherent superposition state

We make a systematic study of high-order harmonic generation (HHG) in a He$^+$-like model ion when the initial states are prepared as a coherent superposition of the ground state and an excited state. It is found that, according to the degree of the ionization of the excited state, the laser intensity can be divided into three regimes in which HHG spectra exhibit different characteristics. The pulse-duration dependence of the HHG spectra in these regimes is studied. We also demonstrate evident advantages of using coherent superposition state to obtain high conversion efficiency. The conversion…

Polarization control of attosecond pulses using bi-chromatic elliptically polarized laser

We study the higher-harmonic generation (HHG) using elliptically polarized two-color driving fields. The HHG via bi-chromatic counter-rotating laser fields is a promising source of circularly polarized ultrashort XUV radiation at the attosecond time scale. The ellipticity or the polarization of the attosecond pulses can be tweaked by modifying the emitted harmonics' ellipticity, which can be controlled by varying the driver fields. We propose a simple setup to control the polarization of the driving fields, which eventually changes the ellipticity of the attosecond pulses. A well-defined scali…

High-order harmonic generation driven by chirped laser pulses induced by linear and non linear phenomena

We present a theoretical study of high-order harmonic generation (HHG) driven by ultrashort optical pulses with different kind of chirps. The goal of the present work is perform a detailed study to clarify the relevant parameters in the chirped pulses to achieve a noticeable cut-off extensions in HHG. These chirped pulses are generated using both linear and nonlinear dispersive media.The description of the origin of the physical mechanisms responsible of this extension is, however, not usually reported with enough detail in the literature. The study of the behaviour of the harmonic cut-off wit…

利用同步中红外和超短紫外激光场产生明亮且可控的孤立阿秒X射线脉冲

Generation of Bright and Controllable Isolated Attosecond X-Ray Pulses from Synchronized Mid-Infrared and Ultra-short Ultraviolet Laser Fields

该研究通过求解氦原子单活性电子近似下的含时薛定谔方程，提出结合中红外驱动场与超短紫外脉冲的双色桌面型高次谐波产生方案，可生成明亮、孤立且可调谐的阿秒X射线脉冲，解决了单色方案的效率与控制问题。