7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Observation of carrier-envelope phase effects in a high-repetition
rate laser-plasma accelerator
Jérôme Faure11LOA, CNRS, Institut Polytechnique de Paris, Palaiseau, Francee-mail (speaker): jerome.faure@ensta.fr
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Laser wakefield acceleration [1] is an emerging
technique for accelerating electron bunches to relativisticenergies in very short distances using ultra-intense laserpulses. It relies on the excitation of an intense plasma
wave, or wakefield, that is able to trap and accelerate
electrons in a single arch of the wakefield, thereby
generating femtosecond relativistic electron bunches.
Because of their extremely short duration and naturalsynchronization with the laser pulse, these electron
bunches are of great interest for probing matter on
femtosecond time scales via pump-probe experiments,
possibly offering unprecedented temporal resolutions forstudies in structural dynamics in condensed matter, e. g.
using ultrafast electron or X-ray diffraction. Lasergenerated electron beams could also be used for highresolution non-destructive testing with gamma-rays forindustrial applications, or also for providing new
radiotherapy protocols with very high energy electrons.
Such applications require high stability, massive data
averaging and would therefore benefit greatly from ahigh repetition rate electron source.
In this context, our group has started the further
miniaturization of laser-plasma accelerators by using
small-scale and high-repetition rate lasers. We use laser
pulses of 3 mJ only and composed of a single optical
cycle (3.5-fs duration) in order to drive a plasma
wakefield accelerator at kHz repetition rate. Electrons
are then trapped and accelerated in the 10 MeV range inless than a hundred microns [2,3]. We will discuss andreview the physics of the various acceleration
mechanisms that allowed us to produce highly stablebeams for up to 12mMillions of shots during more than 5hours [4].
When using near-single-cycle laser pulses, thecarrier-envelope phase (CEP), i.e. the relative position
between the laser envelope and the field oscillation,
starts to matter because it defines the actual waveform ofthe laser electric field. In a series of recent experiments,
we were able to show that the CEP has a clear impact on
the plasma response and the laser plasma acceleration
process [5,6].

Figure 1: Dependence of the electron beam pointing to
the carrier-envelope phase. 1: CEP , 2: CEP, 3:CEPThe beam pointing of the accelerated electron beam
oscillates in phase with the carrier-envelope phase of thelaser, as can be seen in figure 1, while the electron beamenergy depends weakly on the CEP, see figure 2.
Numerical simulations explain this observation throughasymmetries of the plasma waves which are locked tothe carrier-envelope phase. These asymmetries translate
into the off-axis trapping of the electron beam. Theseresults imply that we achieve waveform control ofrelativistic electron dynamics in laser-plasma interaction.
Our results pave the way to high-precision, sub-cycle
control of the electron phase space distribution in plasma
accelerators, enabling the production of attosecond
relativistic electron bunches and x rays.

Figure 2: Dependence of the electron beam energydistribution to the carrier-envelope phase.
References[1] Esarey et al., Rev. Mod. Phys. 81, 1229 (2009)[2] Guénot et al., Nat. Photonics 11, 293 (2017)[3] Faure et al., Plas. Phys. Cont. Fus. 61, 014012 (2019)[4] Rovige et al., PRAB 23, 093401 (2020)[5] Huijts et al., Phys. Rev. X 12, 011036 (2022)[6] Rovige et al., EPJST (2022)