Attosecond pulse characterization

Abstract

Abstract:In this work we propose a novel procedure for the characterization of attosecond pulses. The method relies on the conversion of the attosecond pulse into electron wave-packets through photoionization of atoms in the presence of a weak IR field. It allows for the unique determination of the spectral phase making up the pulses by accurately taking into account the atomic physics of the photoionization process. The phases are evaluated by optimizing the fit of a perturbation theory calculation to the experimental result. The method has been called iPROOF (improved Phase Retrieval by Omega Oscillation Filtering) as it bears a similarity to the PROOF technique [Chini et al. Opt. Express 18, 13006 (2010)]. The procedure has been demonstrated for the characterization of an attosecond pulse train composed of odd and even harmonics. We observe a large phase shift between consecutive odd and even harmonics. The resulting attosecond pulse train has a complex structure not resembling a single attosecond pulse once per IR period, which is the case for zero phase. Finally, the retrieval procedure can be applied to the characterization of single attosecond pulses as well.

High harmonic generation-2ω attosecond stereo-photoionization interferometry in N2

“…Electrons with the same final kinetic energy can be created from three excitation pathways, due to single photon (XUV) or two-photon (XUV ± 400 nm) transitions [28,29]…”

Influence of microscopic and macroscopic effects on attosecond pulse generation using two-color laser fields

“…Moreover, when the polarization of the two fields is the same, attosecond pulses are emitted once per IR optical cycle and hence are carrier-envelop phase stabilized [37]. We note that the temporal structure of attosecond pulse sequences generated by linearly-polarized two-color laser fields has been previously studied with the second-harmonic field strength <0.5% of the IR field, leading to attosecond pulses emitted twice per IR-light cycle [45,46]. However, the macroscopic phase matching conditions under the two-color geometry were not explored in these studies.…”

Benchmarking accurate spectral phase retrieval of single attosecond pulses

“…Equation (31) is the basis of the iPROOF method [48]. In this approximation, the two-photon matrix element can be explicitly separated into two terms: a single XUV photon dipole transition matrix element, times a continuumcontinuum transition amplitude T cc in the presence of an IR field.…”

“…The RABITT method does not work if the harmonics is separated by ω (generated by an ω +2ω two-color field) nor for a single attosecond pulse where the spectral phase information is encoded in the interference between the first-order term from the XUV alone and two second-order terms involving XUV plus IR processes. A phase retrieval method based on analyzing this first-second-order interference (FSI) term was proposed by Laurent et al [48]. They called their method as iPROOF, which was an improved version of the PROOF method (phase retrieval by omega oscillation filtering) proposed by Chini et al [49].…”