Controlling attosecond electron dynamics by phase-stabilized polarization gating

Abstract

A ttosecond electron wavepackets are produced when an intense laser field ionizes an atom or a molecule 1 . 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 possible 2,3 , an isolated attosecond pulse is generated. Here we demonstrate that by modulating the polarization of a carrier-envelope phase-stabilized short laser pulse 4 , 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 timeresolved tomography of atomic or molecular wavefunctions 5,6 and ultrafast dynamics.During high-order harmonic generation (HHG) in gas 7 , short electron wavepackets (EWPs) are periodically released by high-field ionization. Their subsequent coherent interaction with the remaining bound wavefunction leads to coherent extremeultraviolet (XUV) emission. The T 0 /2 periodicity of this process (T 0 being the laser optical period) ensures that only odd harmonics of the fundamental radiation are emitted. Temporally, the XUV pulses are emitted as a train of chirped attosecond pulses [8][9][10] (1 attosecond = 10 −18 s). For both plateau (low energy) and cut-off (high energy) harmonics, specific focusing conditions ensure that only a single attosecond pulse is emitted every half cycle 11,12 . Extracting an isolated attosecond pulse from this train requires breaking the periodicity of the process, so that XUV emission is only possible within a single half cycle of the fundamental pulse. In this way, isolated 250-attosecond-long Figure 1 Spectra generated in argon. Spectra emitted from an argon medium irradiated with a polarization-modulated pulse (τ = 5 fs, δ = 6.2 fs, β = 0 • ) as a function of the CEP shift. For some CEPs, harmonic peaks appear, whereas for other CEPs, they broaden up to a continuum.pulses were recently obtained 13 by selecting the (highly intensity dependent) cut-off harmonics generated in neon by a 5-fs linearly polarized, fundamental pulse with stabilized carrierenvelope phase (CEP). With this technique, the minimum pulse duration achievable is limited by the (∼10 eV) bandwidth of the selected cut-off harmonics, which prevents us reaching the sub-100-attosecond domain.To isolate a broadband attosecond pulse, we used a different approach 2 . Our approach relies on the strong HHG sensitivity on the ellipticity, ε, of the fundamental field, which is largely nature phy...

The simplest route to generating a train of attosecond pulses

“…2 Coherent attosecond laser sources [3][4][5][6][7][8][9][10][11][12] have been realized as part of this research, and on the basis of such technology, various lines of research centered on the ultrafast dynamics of electrons in atoms [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] or molecules 19,20 are being developed. 2 In recent years, through the powering of such attosecond laser sources, 21 nonlinear optics in the attosecond regime are also being explored.…”

Génération d'impulsions attosecondes isolées

“…En modulant la polarisation de ces impulsions de manière à obtenir une porte g < T 0 /2, nous avons clairement pu observer que le spectre XUV émis changeait périodiquement avec la phase absolue [18]. Le spectre observé était un spectre continu pour certaines phases absolues (spectre caractéristique de l'émission d'une impulsion attoseconde isolée) et devenait, après avoir changé la phase absolue de /2, un spectre présentant des structures harmoniques bien définies mais très larges (largeur de 1.6 eV par harmoniques).…”

“…Le spectre observé était un spectre continu pour certaines phases absolues (spectre caractéristique de l'émission d'une impulsion attoseconde isolée) et devenait, après avoir changé la phase absolue de /2, un spectre présentant des structures harmoniques bien définies mais très larges (largeur de 1.6 eV par harmoniques). Les spectres obtenus étaient en bon accord avec nos simulations [18,19] qui montrent que dans le domaine temporel, l'émission XUV est alors constitué soit d'une impulsion attoseconde unique (spectre continu) soit de deux impulsions attosecondes (spectre présentant des structures harmoniques dont la largeur est de 1.6 eV par harmoniques).…”

Carrier-Envelope Phase Stablization of Grating Based High-Power Ultrafast Laser

“…The modulation depth is an indication of the width of the linear polarization gate. For narrower gate widths, the modulation depth would become even stronger while for wider gate widths, the modulation would become shallower and eventually the energy spectrum would exhibit modulations indicative of multiple pulses within the gate (Sola et al, 2006). The attosecond XUV pulses generated under different CEP values are also characterized by the attosecond streak camera.…”