High-order harmonic generation spectroscopy by recolliding electron caustics

D Faccialà,M Devetta,A G Ciriolo,N Dudovich,H Soifer,M Negro,S Pabst,P Prasannan Geetha,C Vozzi,B D Bruner,S Stagira,A Pusala

doi:10.1088/1361-6455/aac351

Abstract

Spectral focusing of the recolliding electron in high-order harmonic generation driven by two-color fields is shown to be a powerful tool for isolating and enhancing hidden spectral features of the target under study. In previous works we used this technique for probing multi-electron effects in xenon and we compared our experimental results with time-dependent configuration-interaction singles calculations. We demonstrate here that this technique can be exploited for reconstructing the enhancement factor of the xenon giant dipole resonance and we discuss the sensitivity of this method to macroscopic effects. We then extend the technique to argon in order to test the applicability of this procedure to other targets.

Highlights

Since its discovery, high-order harmonic generation (HHG) has paved the way towards time-resolving ultrafast electronic processes on the attosecond time scale, in particular thanks to its capacity to generate isolated attosecond pulses in the extreme ultraviolet (EUV) energy range and beyond [1,2,3]
A quantummechanical treatment of the process based on the strong field approximation (SFA) allows the factorization of the HHG spectrum E(Ω) as the product of a recombining electron wave-packet w(Ω) and a photo-recombination transition dipole moment dPW(Ω) from plane-wave continuum states to the bound state [9]
W+c and W-c associated to the two semi-classical cutoffs ÿΩ+ and ÿΩ−, namely upper and lower caustic cutoffs, can be calculated by exploiting the analytic description of HHG by atoms in a two-color field proposed by Frolov et al [24]

Summary

Introduction

High-order harmonic generation (HHG) has paved the way towards time-resolving ultrafast electronic processes on the attosecond time scale, in particular thanks to its capacity to generate isolated attosecond pulses in the extreme ultraviolet (EUV) energy range and beyond [1,2,3]. The dipole dPW(Ω) can be substituted with exact transition dipole moments d(Ω) which use scattering waves instead of plane waves [10, 11], a procedure named quantitative re-scattering theory (QRS) In this framework, in order to collect reliable and significant informations on the target, it is essential to know and control the. Effects within the atomic system that are associated with a specific branch of the caustic can be probed over a wide spectral range We applied this technique to probe the giant dipole resonance (GDR) of xenon, a broad enhancement of the dipole around 100 eV which is due to multi-electronic dynamics involving inner orbitals during the recombination step [12, 20]. We apply this technique to another target, argon, in order to show the versatility of the method that can be applied even to systems that do not show multi-electronic resonances

Method

Xenon case: the giant resonance

Argon case

Conclusions