Measurement of sideband oscillations in two-color photoionization

Divya Bharti, Hemkumar Srinivas, Farshad Shobeiry +7 more

Following up on a previous paper on two-color photoionization of Ar(3p) [D. Bharti , ], we present measurements and calculations for a modified three-sideband (3-SB) version of the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) configuration applied to He(1s) . The 3-SB RABBITT approach allows us to explore interference effects between pathways involving different orders of transitions within the continuum. The relative differences in the retrieved oscillation phases of the three sidebands provide insights into the continuum-continuum transitions. The ground state of helium has zero orbital angular momentum, which simplifies the analysis of oscillation phases and their angle dependence within the three sidebands. We find qualitative agreement between our experimental results and the theoretical predictions for many cases but also observe some significant quantitative discrepancies. Published by the American Physical Society 2024

Alexei N. Grum-Grzhimailo, Грызлова Елена Владимировна, С. И. Страхова +2 more

James A. R. Samson

Michael Meyer, D. Cubaynes, Patrick O’Keeffe +13 more

Two-photon ionization of atomic helium has been measured by combining femtosecond extreme-ultraviolet pulses from the free-electron laser in Hamburg (FLASH at DESY) with intense light pulses from a synchronized neodymium-doped yttrium lithium fluoride laser. Sidebands appear in the photoelectron spectra when the two laser pulses overlap in both space and time. Their intensity exhibits a characteristic dependence on the relative time delay between the ionizing and the dressing pulses and provides an inherent time marker for time-resolved pump-probe experiments. The measurements of the sidebands are in good agreement with theoretical predictions and allow for a direct analysis of two-photon ionization, free from processes related to interference between multiple quantum paths.

R. V. Ambartzumian, N. P. Furzikov, Vladilen S Letokhov +1 more

N M Kabachnik, I P Sazhina

The spin polarization of photoelectrons in two-color XUV + optical multiphoton ionization is theoretically considered using strong field approximation. We assume that both the XUV and the optical radiation are circularly polarized. It is shown that the spin polarization is basically determined by the XUV photoabsorption and that the sidebands are spin polarized as well. Their polarization may be larger or smaller than that of the central photoelectron line depending on the helicity of the dressing field.