Single-photon ionization offers a unique insight into quantum mechanical phenomena in matter, by projecting bound wavefunctions into ionized electronic wavefunctions which can be imaged experimentally. The complex properties of the photo-electron wavefunction are dictated by all steps of the light-matter interaction: the initial state, the properties of the ionizing radiation as well as the complex phase accumulated by the departing electron as it interacts with the Coulomb binding force. Our group develops a variety of measurement and control schemes to probe the photo-ionization process by combining state-of-the-art attosecond metrology with XUV interferometry. Applying these schemes lead to observations of fundamental ultrafast dynamics of photoionization of atomic systems, which have never been resolved before. For example, we could resolve an electronic quantum wavefunction as it is ionized within a fraction of an optical cycle1, or directly determine the absolute phase shift associated with electron-ion scattering2.
1D. Azoury, M. Krüger, G. Orenstein, H. R. Larsson, S. Bauch, B. D. Bruner and N. Dudovich, Nature Communications 8, 1453 (2017).
2 D. Azoury, O. Kneller, S. Rozen, B. D. Bruner, A. Clergerie, Y. Mairesse, B. Fabre, B. Pons, N. Dudovich and M. Krüger, Nature Photonics 13, 54 (2019)
Attosecond Lock-in amplifier – For measuring chirality in the XUV
Chiral effects are of fundamental importance in science, they appear in a wide variety of natural phenomena, from the molecular scale to living organisms. Chiral processes can be probed only by their interaction with other chiral systems, such as circularly polarized light. However, since chiral effects are often intrinsically weak, advanced techniques such as lock-in detection or interferometry have been developed. Such approaches, which rely on the complete polarization control of the interacting light, are crucial for chirality studies. So far, these techniques were accessible only in the visible-IR range, for which the polarization state can be controlled simply by propagating thorough a birefringent medium. Applying this concept in the XUV range, where rich chiral phenomena remains unexplored, is severely limited. We established a direct time-domain approach that allows us to continuously tune the polarization state of XUV light1. We collinearly combine two independent, phase-locked, orthogonally polarized HHG sources, and control their relative delay with sub-cycle accuracy. We achieve direct and simple control over the fundamental ingredients of a polarized source—relative field strength and relative phase between two orthogonal XUV fields, mimicking a birefringent medium (see illustration). Scanning of the delay between the two independent sources allows the periodic modulation of the polarization state, while maintaining a constant intensity. Such complete polarization control allows realization of the lock-in detection scheme in the XUV regime1.
1 D. Azoury, O. Kneller, M. Krüger, B. D. Bruner, O. Cohen, Y. Mairesse and N. Dudovich, accepted