Photoemission by Large Electron Wave Packets

N. Mårtensson, Martin Weinelt, Olof Karis +5 more

Charles Bourassin-Bouchet, Lou Barreau, Vincent Gruson +4 more

Laser-dressed photoemission spectroscopy has established itself as the gold standard of attosecond temporal metrology.In this technique, the attosecond structure of an extreme-ultraviolet pulse is retrieved from the wave function of the electron wave packet released during photoionization.Here, we show that this electron wave packet should rather be described using the density matrix formalism, thus allowing one to account for all processes that can affect its coherence, from the attosecond pulse generation to the photoemission and the measurement processes.Using this approach, we reconstruct experimentally a partially coherent electron wave packet with a purity of 0.11 (1 for full coherence).Comparison with theoretical models then allows us to identify the origins of this decoherence and to overcome several limitations such as beam-line instabilities or spectrometer resolution.Furthermore, we show numerically how this method gives access to the coherence and eigencomponents of complex photoelectron wave packets.It thus goes beyond the current measurement of photoionization time delays and provides a general framework for the analysis and understanding of complex photoemission processes.

Divya Bharti, J. C. del Valle, Aaron Bondy +4 more

Scattering theory has long established that wave packets can experience time delays and advances, while developments in attosecond interferometry have made such temporal shifts experimentally accessible. They are encoded in the spectral phase of the emitted electron wave packet and are commonly accessed through interferometric techniques. Here, we report an intensity-driven reversal of the angular phase of a threshold photoelectron sideband in helium. By varying the intensity of an infrared dressing field, we control the direction of the phase change at large emission angles, which is associated with interference between partial waves near angular nodes. Solving the time-dependent Schrödinger equation within the single-active-electron approximation confirms the existence of an angular phase inversion. Our results reveal a mechanism for manipulating the angular phase structure of photoelectron wave packets over a large range via laser-induced interference.

FRANZ HASSELBACH

Norikazu Tomita, Masahiro Yamazaki, Keiichirō Nasu

Justin B. Peatross, John Corson, Grayson J. Tarbox

Interference in the far-field radiation pattern emitted from a classical current distribution implies near-field work between different spatial portions of the distribution. We examine this relationship and the essential role of system geometry for the case of two oscillating dipoles and for a Gaussian current distribution. This analysis offers a compelling argument as to why the radiation from a large single-electron quantum wave packet should not exhibit the same destructive interference as that associated with a comparable classical charge density. Our discussion draws attention to the ad hoc heuristics motivating the original derivation of a quantum electron's radiation profile.