Special Seminar: "Multiphoton Kramers-Heisenberg Formula for Describing High-Harmonic Generation." (Prof. Sándor Varró)

Date: Jul 9, 2024
Time: 11:00 AM (Local Time Germany)
Speaker: Prof. Sándor Varró
ELI-ERIC, ALPS (Attosecond Light Pulse Source), ELI-HU Szeged, Hungary
Location: Max Planck Institute of Quantum Optics
Room: Herbert Walther Lecture Hall

Abstract. We discuss the question of how can one treat the laser-induced (or laser-assisted)high-order processes of electrons (bound or free) nonperturbatively, in such a way that boththe electron-atom interaction and the quantized nature of radiation be simultaneously takeninto account? An analytic method is proposed to answer this question in the generalframework of nonrelativistic quantum electrodynamics. As an application, a quantum opticalgeneralization of the strong-field Kramers-Heisenberg formula has been derived fordescribing high-harmonic generation (HHG).

A semiclassical version of a similar Kramers-
Heisenberg formula has already been published long ago [1], which inherently contain the
appearance of the plateau in the HHG spectrum, and the optional appearance of a Cooper
minimum [2]. Beyond these, the new quantum formula [3] is suitable to analyse (among
various quantal effects, like depletion) the role of arbitrary photon statistics of the incoming
field, and the amplification of the high-order harmonics, due to stimulated emission [4].

References. [1] Varró S. and Ehlotzky F. A new integral equation for treating high-intensity
multiphoton processes. Il Nuovo Cimento, 15 D, 1371-1396 (1993). [2] See e.g. Schoun S B,
Chirla R, Wheeler J, Roedig C, Agostini P and DiMauro L F, Attosecond pulse shaping
around a Cooper minimum. Phys. Rev. Lett. 112, 153001 (2014). [3] Varró S, Quantum
optical aspects of high-harmonic generation. Photonics 8 (7), 269 (2021). [4] Varró S,
Coherent and incoherent superposition of transition matrix elements of the squeezing
operator. New Journal of Physics 24, 053035 (2022).
Acknowledgments. Support by the ELI-ALPS project is acknowledged. The ELI-ALPS
Project No. GINOP 2.3.6-15 is supported by the European Union and co-financed by the
European Regional Development Fund.