Angularly Resolved RABBITT at 2ω: Attosecond Pulses Measurement & Attosecond Signature in the 1s3p Resonance of Helium

Abstract

The Reconstruction of Attosecond Harmonic Beating By Interference of Two-photon Transition (RABBITT) method [1–3] is nowadays routinely used in attosecond physics to retrieve the temporal profile of an attosecond pulse train (APT) generated by high harmonic generation. It is employed to measure the ionization/Wigner time [4] of an escaping electron that scatters in the potential of its parent atom or molecule [5]. The RABBITT signal is obtained by measuring the time-resolved photoelectron spectrum of a given target that interacts with an APT (composed of odd harmonics of the fundamental laser frequency (ω 0 ) dressed by a femtosecond pulse at the frequency ω 0 . In the spectral domain, several quantum paths lead to the same electron kinetic energy (Fig. 1.(c)) these paths interfere leading to an oscillation of the electron yield at twice the fundamental frequency with a phase that depends on the (i) phase of the harmonic, (ii) the phase of the IR transition (so called continuum-continuum phase) and (iii) the atomic or molecular phase that corresponds to the transition induced by the XUV. In the temporal domain, one attosecond pulse appears for each half optical cycle of the dressing pulse as shown in Fig. 1(a).