## Professor Carla Figueira de Morisson Faria

*Department of Physics, University College London, United Kingdom*

The theoretical modelling of matter in strong laser fields (intensities of typically 1013W/cm2 or higher) has posed many challenges since the inception of this research area, in the early 1990s. Not only are the field strengths involved comparable to the target’s binding forces, but the timescales involved are extremely short, of the order of hundreds of attoseconds (10-18 s). In principle, these timescales allow resolving and ultimately steering electron dynamics in real time, which has become one of the main goals of attoscience [1]. Apart from purely numerical and/or ab-initio methods, orbit-based, semi-analytical methods are hugely popular, and some of them, such as the strong-field approximation (SFA) [2], have helped set the paradigms behind strong-field phenomena, which are described as laser-induced recollision of recombination of an electron with its parent ion, and provides a very intuitive picture of quantum interference. The SFA, however, approximates the continuum by field-dressed plane waves, and this approximation is no longer sufficient for describing a wide range of phenomena. This has led to the development of a multitude of theoretical methods beyond the SFA, which incorporate the residual binding potentials [3].

In my talk, I will review the main orbit-based methods employed in my research field, starting from the SFA and going beyond. I will start by providing an overview of the landscape, as far as the main approaches are concerned, and, subsequently, I will delve deeper in a method developed by my group at UCL, the Coulomb-Quantum Orbit Strong-Field Approximation [4]. Thereafter, I will illustrate the CQSFA’s capabilities using applications to ultrafast photoelectron holography, in which a myriad of holographic structures, known and overlooked, were traced back to specific types of quantum interference [5]. Finally, I will discuss some imaging applications in joint theory-experiment work [6].

### References:

[1] Ferenc Krausz and Misha Ivanov, “Attosecond Physics”, Rev. Mod. Phys.**81**, 163 (2009); Franck Lépine, Misha Y. Ivanov, Marc J. J. Vrakking, “Attosecond molecular dynamics: fact or fiction?”, Nature Photonics**8**, 195 (2014)

[2] S V Popruzhenko, “Keldysh theory of strong field ionization: history, applications, difficulties and perspectives”, J. Phys. B**47**, 20400 (2014); Kasra Amini et al, “Symphony on strong field approximation”, Rep. Prog. Phys.**82**, 116001 (2019)

[3] C Figueira de Morisson Faria, AS Maxwell, ``It is all about phases: ultrafast holographic photoelectron imaging", Rep. Prog. Phys.**83** (3), 034401 (2020)

[4] X. Lai, C. Poli, H. Schomerus and C. Figueira de Morisson Faria, "Influence of the Coulomb potential on above-threshold ionization: a quantum-orbit analysis beyond the strong-field approximation", Phys. Rev. A**92**, 043407 (2015)

[5] A. S. Maxwell, A. Al-Jawahiry, T. Das, and C. Figueira de Morisson Faria, ``Coulomb-corrected quantum interference in above-threshold ionization: Working towards multitrajectory electron holography", Phys. Rev. A**96**, 023420 (2017)

[6] HuiPeng Kang, et al, ``Holographic detection of parity in atomic and molecular orbitals", Phys. Rev. A**102**, 013109 (2020); Andrew S. Maxwell, et al, "Spiral-like holographic structures: Unwinding interference carpets of Coulomb-distorted orbits in strong-field ionization", Phys. Rev. A**102**, 033111 (2020); Nicholas Werby, et al, "Dissecting Sub-Cycle Interference in Photoelectron Holography", Phys. Rev. A**104**, 013109 (2021)