Summary form only given. Fundamental processes in atoms, molecules, as well as condensed matter are triggered or mediated by the motion of electrons inside or between atoms. Electronic dynamics on atomic length scales tends to unfold within tens to thousands of attoseconds (1 attosecond [as] = 10-18 s). Recent breakthroughs in laser science are now opening the door to watching and controlling these hitherto inaccessible microscopic dynamics. The key to accessing the attosecond time domain is the control of the electric field of (visible) light, which varies its strength and direction within less than a femtosecond (1 femtosecond = 1000 attoseconds). Atoms exposed to a few oscillations cycles of intense laser light are able to emit a single extreme ultraviolet (XUV) burst lasting less than one femtosecond. Full control of the evolution of the electromagnetic field in laser pulses comprising a few wave cycles have recently allowed the reproducible generation and measurement of isolated sub-femtosecond XUV pulses, demonstrating the control of microscopic processes (electron motion and photon emission) on an attosecond time scale. These tools have enabled us to visualize the oscillating electric field of visible light with an attosecond "oscilloscope", to control single-electron and probe multi-electron dynamics in atoms, molecules and solids. Recent experiments hold promise for the development of an attosecond X-ray source, which may pave the way towards 4D electron imaging with sub-atomic resolution in space and time.

Attosecond Physics

We generated single-cycle isolated attosecond pulses around ∼36 electron volts using phase-stabilized 5-femtosecond driving pulses with a modulated polarization state. Using a complete temporal characterization technique, we demonstrated the compression of the generated pulses for as low as 130 attoseconds, corresponding to less than 1.2 optical cycles. Numerical simulations of the generation process show that the carrier-envelope phase of the attosecond pulses is stable. The availability of single-cycle isolated attosecond pulses opens the way to a new regime in ultrafast physics, in which the strong-field electron dynamics in atoms and molecules is driven by the electric field of the attosecond pulses rather than by their intensity profile.

https://science.sciencemag.org/content/sci/314/5798/443.full.pdf

Isolated Single-Cycle Attosecond Pulses

We would like to make corrections to three equations in the above article Please see the PDF file for full details

https://iopscience.iop.org/article/10.1088/0034-4885/67/6/R01/pdf

The physics of attosecond light pulses

Attosecond electron wavepackets are produced when an intense laser field ionizes an atom or a molecule1. When the laser field drives the wavepackets back to the parent ion, they interfere with the bound wavefunction, producing coherent subfemtosecond extreme-ultraviolet light bursts. When only a single return is possible2,3, an isolated attosecond pulse is generated. Here we demonstrate that by modulating the polarization of a carrier-envelope phase-stabilized short laser pulse4, we can finely control the electron-wavepacket dynamics. We use high-order harmonic generation to probe these dynamics. Under optimized conditions, we observe the signature of a single return of the electron wavepacket over a large range of energies. This temporally confines the extreme-ultraviolet emission to an isolated attosecond pulse with a broad and tunable bandwidth. Our approach is very general, and extends the bandwidth of attosecond isolated pulses in such a way that pulses of a few attoseconds seem achievable. Similar temporal resolution could also be achieved by directly using the broadband electron wavepacket. This opens up a new regime for time-resolved tomography of atomic or molecular wavefunctions5,6 and ultrafast dynamics.

/pdf/controlling-attosecond-electron-dynamics-by-phase-stabilized-20pg5twtuw.pdf

Controlling attosecond electron dynamics by phase-stabilized polarization gating

Attosecond science offers formidable tools for the investigation of electronic processes at the heart of important physical processes in atomic, molecular and solid-state physics. In the last 15 years impressive advances have been obtained from both the experimental and theoretical points of view. Attosecond pulses, in the form of isolated pulses or of trains of pulses, are now routinely available in various laboratories. In this review recent advances in attosecond science are reported and important applications are discussed. After a brief presentation of various techniques that can be employed for the generation and diagnosis of sub-femtosecond pulses, various applications are reported in atomic, molecular and condensed-matter physics.

https://iopscience.iop.org/article/10.1088/0953-4075/49/6/062001/pdf

Advances in attosecond science

We generate high-order harmonics by using an 800-nm fundamental pulse whose polarization evolves with time. Controlling the ellipticity modulation of the fundamental field allows us to continuously confine the harmonic emission from an estimated minimum value of 7 fs $(1\mathrm{fs}{=10}^{\ensuremath{-}15}\mathrm{s})$ up to more than the 35 fs input pulse duration. Depending on the observed harmonic, the harmonic spectrum can show either a narrowing or a broadening when the ellipticity is changed in good agreement with an effective confinement of the high-order harmonic generation.

/pdf/time-gated-high-order-harmonic-generation-1opyz6hlvc.pdf

Time-gated high-order harmonic generation

Les harmoniques d'ordres eleves, produites lors de l'interaction entre un laser impulsionnel intense et un milieu gazeux, sont emises dans le domaine temporel sous forme d'un train d'impulsions attosecondes espacees d'une demi periode optique du champ laser. La production d'une seule impulsion attoseconde permettrait d'acceder a des resolutions temporelles jusqu'ici inaccessibles pour des etudes resolues en temps. D'apres les simulations, une des solutions pour atteindre cet objectif est de confiner la generation d'harmoniques sur moins d'un cycle optique du laser fondamental. Dans ce manuscrit, nous presentons une methode qui permettrait de restreindre l'emission harmonique a une seule impulsion. Elle repose sur l'extreme sensibilite de la generation d'harmoniques a la polarisation. Nous avons developpe une technique originale permettant de moduler temporellement la polarisation d'une impulsion laser infra-rouge. Dans un premier temps, nous avons etudie les modifications spectrales des harmoniques generees par cette impulsion modulee en polarisation. Dans un second temps, nous avons realise une mesure directe des impulsions harmoniques obtenues en modulant temporellement l'etat de polarisation de l'impulsion laser. Nous avons observe clairement un confinement de la generation d'harmoniques. Ce travail a permis de fixer a environ 10 fs la duree maximale que l'impulsion infrarouge doit avoir pour obtenir une seule impulsion attoseconde. Dans ce cadre, nous avons developpe au laboratoire une technique originale de post-compression d'impulsion laser pour obtenir des impulsions haute energie sub-10 fs.

/pdf/confinement-temporel-de-la-generation-d-harmoniques-d-ordre-4qg9ouzo17.pdf

J. Plumridge

Papers

Time-gated high-order harmonic generation

Confinement temporel de la génération d'harmoniques d'ordre élevé