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Quantum-classical correspondence in high harmonic generation

Focus

Strong field physics, which focuses on the interaction between very strong and very short laser pulses and atoms and molecules, has revealed the possibility for producing photons with extremely short wavelengths, opening the way to attosecond science. Common techniques for producing such ultra-short laser sources rely on the so-called high harmonic generation (HHG) phenomenon. At the heart of HHG is the recollision scenario where an electron, previously ionized and accelerated by the laser field, is hurled back at its parent ion and collides with it. Initially designed for linearly polarized laser fields, classical analyses have extended the recollision picture to circular polarization as well. Yet the question of whether it could lead to HHG or not remained opened. In this paper, using quantum mechanical simulations, we show that atomic HHG is indeed possible with circular polarization, provided the system is initialized appropriately. We also show that the properties of HHG spectra are closely related to specific classical periodic orbits that organize recollision with circular polarization. This connection is at the center of the quantum-classical correspondence we reveal here. Finally, the robustness of the process with parameters should allow for experimental verification.

Associated publications

Recollision Scenario without Tunneling: Role of the Ionic Core Potential

posted May 13, 2016, 11:07 PM by François Mauger   [ updated May 13, 2016, 11:19 PM ]

Abstract

We present a purely classical recollision scenario, i.e., without tunneling, which, in contrast to the standard three-step model, takes into account the ionic core potential fully at all stages of the recollision process and is valid at all intensities. We find that a key periodic orbit drives the recollisions by guiding electrons away and back to the core. At sufficiently high intensity, we connect our scenario to the three-step model, and explain why the three-step model leads to good agreement with the cutoff in high harmonic generation despite neglecting the core potential after tunneling.

Reference

A. Kamor, C. Chandre, T. Uzer, and F. Mauger - Recollision Scenario without Tunneling: Role of the Ionic Core Potential - Physical Review Letters 112, 133003 (2014)

Quantum-classical correspondence in circularly polarized high harmonic generation

posted May 13, 2016, 11:03 PM by François Mauger   [ updated May 13, 2016, 11:18 PM ]

Abstract

Using numerical simulations, we show that atomic high order harmonic generation (HHG) with a circularly polarized laser field offers an ideal framework for quantum-classical correspondence in strong field physics. With an appropriate initialization of the system, corresponding to a superposition of ground and excited state(s), simulated HHG spectra display a narrow strip of strong harmonic radiation preceded by a gap of missing harmonics in the lower part of the spectrum. In specific regions of the spectra, HHG tends to lock to circularly polarized harmonic emission. All these properties are shown to be closely related to a set of key classical periodic orbits that organize the recollision dynamics in an intense, circularly polarized field.

Reference

F. Mauger, A.D. Bandrauk, A. Kamor, T. Uzer, and C. Chandre - Quantum-classical correspondence in circularly polarized high harmonic generation - Journal of Physics B: Atomic, Molecular and Optical Physics 47, 041001 (2014)

Outreach

  • Video abstract: Quantum-classical correspondence in circularly polarized high harmonic generation
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