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Recollision with circular polarization

Focus

What do asteroid capture and double ionization have in common? A great deal, it turns out:  A circularly polarized (CP) laser field hurls ionized electrons back at the core in the same way that comets and interplanetary debris make their way to planets. According to conventional wisdom, a CP field suppresses collision-induced double ionization and high harmonic generation since ionized electrons spiral away and therefore cannot revisit the core. A few experiments carried out with rare gas atoms in the past confirmed this belief, and the matter would rest there if it weren't for conflicting experiments showing the signature of electron-electron correlation in the double ionization of magnesium. We reconcile these seemingly contradictory results by finding the conditions for an ionized electron to revisit the core to ionize more electrons (or recombine to generate high harmonics). Ionized electrons can return through a moving saddle point which arises from the joint actions of the Coulomb potential and the laser field. Our results imply that the so-called "recollision" or "three-step" model, which is the keystone of strong field physics in linearly polarized fields, can also be valid in circularly polarized ones.

Associated publications

How Key Periodic Orbits Drive Recollisions in a Circularly Polarized Laser Field

posted May 14, 2016, 11:54 AM by François Mauger   [ updated May 14, 2016, 11:55 AM ]

Abstract

We show that a family of key periodic orbits drives the recollision process in a strong circularly polarized laser field. These orbits, coined recolliding periodic orbits, exist for a wide range of parameters, and their relative influence changes as the laser and atomic parameters are varied. We find the necessary conditions for recollision-driven nonsequential double ionization to occur. The outlined mechanism is universal in that it applies equally well beyond atoms: The internal structure of the target species plays a minor role in the recollision process.

Reference

A. Kamor, F. Mauger, C. Chandre, and T. Uzer - How Key Periodic Orbits Drive Recollisions in a Circularly Polarized Laser Field - Physical Review Letters 110, 253002 (2013)

Recollisions and Correlated Double Ionization with Circularly Polarized Light

posted May 14, 2016, 11:48 AM by François Mauger   [ updated May 14, 2016, 11:56 AM ]

Abstract

It is generally believed that the recollision mechanism of atomic nonsequential double ionization is suppressed in circularly polarized laser fields because the returning electron is unlikely to encounter the core. On the contrary, we find that recollision can and does significantly enhance double ionization, even to the extent of forming a ‘‘knee,’’ the signature of the nonsequential process. Using a classical model, we explain two apparently contradictory experiments, the absence of a knee for helium and its presence for magnesium.

Reference

F. Mauger, C. Chandre, and T. Uzer - Recollisions and Correlated Double Ionization with Circularly Polarized Light - Physical Review Letters 105, 083002 (2010)

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