Amplification of intense light fields by nearly free electrons

Abstract

Light can be used to modify and control properties of media, as in the case of electromagnetically induced transparency or, more recently, for the generation of slow light or bright coherent XUV and X-ray radiation. Particularly unusual states of matter can be created by light fields with strengths comparable to the Coulomb field that binds valence electrons in atoms, leading to nearly-free electrons oscillating in the laser field and yet still loosely bound to the core [1,2]. These are known as Kramers-Henneberger states [3], a specific example of laser-dressed states [2]. Here, we demonstrate that these states arise not only in isolated atoms [4,5], but also in rare gases, at and above atmospheric pressure, where they can act as a gain medium during laser filamentation. Using shaped laser pulses, gain in these states is achieved within just a few cycles of the guided field. The corresponding lasing emission is a signature of population inversion in these states and of their stability against ionization. Our work demonstrates that these unusual states of neutral atoms can be exploited to create a general ultrafast gain mechanism during laser filamentation.

Locally and globally chiral fields for ultimate control of chiral light matter interaction

“…h (3) describes perturbative enantio-sensitive three-photon light matter interaction. For example, it appears as a light pseudoscalar in absorption circular dichroism in the electric-dipole approximation, analogously to how the helicity of circularly polarized light contributes to standard absorption circular dichroism beyond the electric-dipole approximation.…”

“…Equation (14) shows that enantio-sensitive light absorption is controlled by the third-order correlation function h (3) in Eq. ( 1).…”

“…Eq. (3) shows that the ω-2ω field also forms a local chiral coordinate frame, and we can identify three non-coplanar vectors upon temporal averaging. Here, the system absorbs three photons of frequency ω with x polarization, emits one photon of frequency ω with y polarization and emits one 2ω photon with z polarization.…”

“…A non-zero triple product means that the field trajectory defines a local chiral reference frame via the three non-coplanar vectors F(ω 1 ), F(ω 2 ) and F(ω 1 + ω 2 ). This is why to have non-zero h (3) , a locally chiral field needs at least three different frequency components. h (3) governs perturbative light-matter interaction, such as absorption circular dichroism induced solely by laser electric fields (see Methods) and enantiosensitive population of rotational states in chiral molecules 26 using microwave fields.…”

A dynamical symmetry triad in high-harmonic generation revealed by attosecond recollision control

“…Notably, the observed phenomenon gives robust access to chiral processes with few-attosecond time precision.The concept of emergence describes the appearance of entirely new properties of a coupled system, which only arise from the interaction of its constituents. In light-matter interaction, emergent phenomena are particularly prominent in strongly driven states of matter, as evident in light-induced variants of superconductivity [1], the Hall effect [2], and topological insulators [3] in the condensed phase, as well as exceptional points in molecules [4,5], Kramers-Henneberger states in gases [6,7], and time-crystals in isolated many-body systems [8,9]. Such emergent states are often governed by novel symmetry properties and topologies, which may be probed by external or emitted radiation fields.…”