Attosecond Lighthouses: How To Use Spatiotemporally Coupled Light Fields To Generate Isolated Attosecond Pulses

Abstract

Coherent light beams composed of ultrashort pulses are now increasingly used in different fields of Science, from time-resolved spectroscopy to plasma physics. Under the effect of even simple optical components, the spatial properties of these beams can vary over the duration of the light pulse [1]. In this letter, we show how such spatio-temporally coupled electromagnetic fields can be exploited to produce an attosecond lighthouse, i.e. a source emitting a collection of isolated attosecond pulses, propagating in angularly well-separated light beams. This very general effect not only opens the way to a new generation of attosecond light sources, particularly suitable for pump-probe experiments, but also provides a powerful new tool for ultrafast metrology, for instance giving direct access to fluctuations in the phase of the laser field oscillations with respect to the pulse envelop, right at the focus of even the most intense ultrashort laser beams. PACS numbers:Ultrashort light beams are said to exhibit spatiotemporal couplings (STC) when their spatial properties depend on time, and conversely [1] -i.e. their electric field E(x, y, z = z 0 , t) = E 1 (t)E 2 (x, y). The importance of STC has been largely overlooked in most laser-matter interaction experiments, until recently [2]. In strong-field science, STC are even considered as highly detrimental, because they systematically decrease the peak intensity at focus [3]. In this letter, we show that on the opposite, moderate and controlled STC provide a powerful means of controlling high-intensity laser-matter interactions, and pave the way to a whole range of new experimental capabilities.To demonstrate this idea, we consider a particular application of STC to attosecond pulse generation (1 as=10 −18 s), which has been the key issue in the development of attosecond Science [4]. All attosecond light sources demonstrated so far are based on high-order harmonic generation (HHG) of intense femtosecond laser pulses in different media [4,5]. Since many-cycle long pulses naturally produce trains of attosecond pulses, considerable efforts had to be deployed in the last fifteen years for the development of 'temporal gating' techniques, to isolate single attosecond pulses, more readily usable for time-resolved measurements of electron dynamics in matter. A variety of experimentally-challenging techniques have now been demonstrated for HHG in gases [6,7]. In contrast, the problem is still unsolved experimentally for HHG on plasma mirrors [8][9][10], one of the promising processes to obtain the next generation of attosecond light sources [11,12]. We describe here how STC provide a new approach to this problem, of unprecedented simplicity, generality and potential : one of the most basic types of STC, wavefront rotation [1] (WFR), can be exploited to generate a collection of single attosecond pulses in angularly well-separated light beams -an attosecond lighthouse-even with relatively long laser pulses.Let us first briefly summarize the concept of WFR at the focus of a femto...

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“…• Une modulation de la densité d'émet-teurs ou des conditions d'émission qui sont influencées par l'ionisation du milieu. • Une modulation de la direction d'émis-sion des impulsions qui, grâce à la cohé-rence spatiale du processus, peut être contrôlée en jouant sur le front de phase du fondamental (phare attoseconde) (Vincenti et Quéré, 2012). …”

Pseudospectral Maxwell solvers for an accurate modeling of Doppler harmonic generation on plasma mirrors with particle-in-cell codes

“…If the laser injection and the target design are carefully chosen to induce a reflection along one of the diagonal, a resolution of λ/140 would be enough to reduce numerical dispersion effects on the harmonic beams. However, for highly diverging harmonic beams or interaction configurations involving the emission of harmonic beams at many different angles [12,34], numerical dispersion could still severely affect harmonic beam properties. In addition, another practical problem is to redesign all the simulation and the diagnostics every time the angle of incidence or the Maxwell solver is changed which can be challenging for parametric studies.…”

“…A lot of physical information from the laser-plasma interaction is "encoded" in the harmonic spectrum which can then be used as a probe of the relativistic plasma mirror dynamics [12][13][14]. The second motivation is to use this radiation source for performing innovative time-resolved application experiments.…”

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