Polarisation response of delay dependent absorption modulation in strong field dressed helium atoms probed near threshold

Abstract

We present the first measurement of the vectorial response of strongly dressed helium atoms probed by an attosecond pulse train (APT) polarised either parallel or perpendicular to the dressing field polarisation. The transient absorption is probed as a function of delay between the APT and the linearly polarised 800 nm field of peak intensity´-1.3 10 W cm 14 2 . The APT spans the photon energy range 16-42 eV, covering the first ionisation energy of helium (24.59 eV). With parallel polarised dressing and probing fields, we observe modulations with periods of one half and one quarter of the dressing field period. When the polarisation of the dressing field is altered from parallel to perpendicular with respect to the APT polarisation we observe a large suppression in the modulation depth of the above ionisation threshold absorption. In addition to this we present the intensity dependence of the harmonic modulation depth as a function of delay between the dressing and probe fields, with dressing field peak intensities ranging from 2×10 12 to 2×10 14 -W cm 2 . We compare our experimental results with a full-dimensional solution of the single-atom time-dependent (TD) Schrödinger equation obtained using the recently developed abinitio TD B-spline ADC method and find good qualitative agreement for the above threshold harmonics.

Self-probing spectroscopy of XUV photo-ionization dynamics in atoms subjected to a strong-field environment

“…Therefore we decided to exclude the 6 ω IR Fourier data from the reconstruction procedure; the remaining data are sufficient for the least-square fit. The strong 6 ω IR component of H19 has a different origin; it is due to interference between the XUV-initiated harmonic light and the background harmonic from the ionizing APT 40 .…”

Onset of ionic coherence and ultrafast charge dynamics in attosecond molecular ionisation

“…Tel: 0044 20 7589 47728; E-mail: m.ruberti11@imperial.ac.uk using both table-top high harmonic generation (HHG) [30][31][32][33][34][35][36] and free-electron laser (FEL) sources [37][38][39][40][41][42][43] , that would open the way to attosecond pump-attosecond probe experiments. Following this rapid progress 44,45 , several time-resolved spectroscopic techniques have been developed 18,19,[46][47][48][49][50][51][52][53][54][55] and have demonstrated unprecedented temporal resolution 14,57,58 in real-time tracing of both valence and core coherent electron dynamics as well as nuclear motion 56 . In particular, first experimental evidence of pure electronic, few-fs, charge oscillations after ionisation of the phenylalanine molecule 18 and the iodoacetylene molecule 19 were recently reported.…”

A detailed investigation of single-photon laser enabled Auger decay in neon

“…We calculated the single-atom, phase-dependent, channel-resolved asymmetry using the time-dependent (TD) B-spline algebraic diagrammatic construction (ADC) ab initio method [14][15][16][17]. The single-particle basis set consists of spherical harmonics Y lm (θ, j) for the angular part and B-spline functions B i (r) for the radial coordinate.…”