Synopsis: Keeping track of electronic paths with attosecond resolution

A full quantum mechanical description of how light interacts with matter in higher-harmonic generation may lead to better control over the production of isolated and sequential attosecond ultraviolet pulses.
Synopsis figure
Illustration: T. Auguste et al., Phys. Rev. A (2009)

High-harmonic generation, a nonlinear optical process that occurs when a short burst of intense light irradiates a target, is an important method for producing attosecond (10-18s) length pulses of extreme ultraviolet (XUV) light. Classically, the light pulse ejects an electron from an atom in the target material into the continuum. When this electron is accelerated and then driven back to the parent ion by the laser field, the recombination of the electron with the ion leads to the emission of XUV light.

The quantum mechanical version of this process is somewhat of a generalization of the classical picture: the process is a coherent sum over all possible electron paths that the electron takes on its excursion from the atom. At high enough intensities, the wave function describing the atom and its associated electron is a sum over interferences between a “short” path (when the electron excursion time is a half laser cycle) and a “long” path (when the excursion time is close to a full laser cycle).

Until now, these interferences have not been observed because they are smoothed out in the collective response of the macroscopic XUV generating medium, which is typically a jet of gas. However, in a paper appearing in Physical Review A, Thierry Auguste and colleagues at the CEA in Saclay, France, and a team of researchers from France, the UK, and Switzerland have now demonstrated both theoretically and experimentally how to observe these interferences. They measure the quantum path interferences by properly spectrally and spatially filtering the XUV light generated from a pulsed argon jet irradiated by a focused high-intensity Ti:Sapphire laser.

These results demonstrate a mechanism to control the electron trajectory—and hence the higher harmonics of light emitted by its oscillation—with an accuracy approaching tens of attoseconds. – Frank Narducci


Features

More Features »

Announcements

More Announcements »

Subject Areas

Optics

Previous Synopsis

Atomic and Molecular Physics

Dressing a boson in a sea of fermions

Read More »

Next Synopsis

Related Articles

Focus: A Tiny Engine Powered by Light and Liquid Physics
Statistical Physics

Focus: A Tiny Engine Powered by Light and Liquid Physics

A micrometer-sized sphere trapped by optical tweezers in a liquid, under the right conditions, orbits rapidly around the laser beam—creating a potential micromixing device. Read More »

Viewpoint: Intense Laser Sheds Light on Radiation Reaction
Plasma Physics

Viewpoint: Intense Laser Sheds Light on Radiation Reaction

Experimentalists have used ultraintense laser light to explore a fundamental problem in quantum electrodynamics: the response of an accelerated electron to the radiation it emits. Read More »

Synopsis: Detecting Energy-Time Entanglement
Quantum Information

Synopsis: Detecting Energy-Time Entanglement

A new detection system directly observes a type of entanglement in which a photon’s energy is correlated with the time its partner is detected.  Read More »

More Articles