Vacuum laser acceleration of super-ponderomotive electrons using relativistic transparency injection

P K Singh,A Moreau,H Song,S Wang,R Hollinger,C Calvi,F.-Y Li,S Palaniyappan,R E Reinovsky,Y Wang,J J Rocca,A Favalli,A Junghans,C.-K Huang

doi:10.1038/s41467-021-27691-w

P K Singh, A Moreau + Show 12 more

Open Access

https://doi.org/10.1038/s41467-021-27691-w

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Abstract

Intense lasers can accelerate electrons to very high energy over a short distance. Such compact accelerators have several potential applications including fast ignition, high energy physics, and radiography. Among the various schemes of laser-based electron acceleration, vacuum laser acceleration has the merits of super-high acceleration gradient and great simplicity. Yet its realization has been difficult because injecting free electrons into the fast-oscillating laser field is not trivial. Here we demonstrate free-electron injection and subsequent vacuum laser acceleration of electrons up to 20 MeV using the relativistic transparency effect. When a high-contrast intense laser drives a thin solid foil, electrons from the dense opaque plasma are first accelerated to near-light speed by the standing laser wave in front of the solid foil and subsequently injected into the transmitted laser field as the opaque plasma becomes relativistically transparent. It is possible to further optimize the electron injection/acceleration by manipulating the laser polarization, incident angle, and temporal pulse shaping. Our result also sheds light on the fundamental relativistic transparency process, crucial for producing secondary particle and light sources.

Highlights

Intense lasers can accelerate electrons to very high energy over a short distance
Existing schemes of laser-based electron acceleration fall into two broad categories: (1) Laser Wakefield Acceleration (LWFA)[13,14,15,16,17] that uses the plasma wakefield (~10 GV/m) driven by the laser to accelerate the electrons and (2) Direct or Vacuum Laser Acceleration (DLA or VLA)[18,19,20,21,22,23,24,25,26,27,28] where the injected electrons are directly accelerated by the intense laser field (>10 TV/m)
We demonstrate VLA of electrons up to 20 MeV using a qualitatively different injection method that exploits the plasma relativistic transparency (RT) effect38––where dense opaque plasma becomes transparent to the driving laser due to relativistic electron mass increase––by driving a thin solid foil at normal laser incidence

Summary

Introduction

Intense lasers can accelerate electrons to very high energy over a short distance. Such compact accelerators have several potential applications including fast ignition, high energy physics, and radiography. Table-top petawatt-class lasers provide a large electric field (>10 TV/m) capable of accelerating electrons to near-light speed over a very short distance[1,2,3,4,5] Such compact accelerators have several potential applications including fast ignition, high energy physics, radiography, and secondary ion/neutron sources[6,7,8,9,10,11,12]. Existing schemes of laser-based electron acceleration fall into two broad categories: (1) Laser Wakefield Acceleration (LWFA)[13,14,15,16,17] that uses the plasma wakefield (~10 GV/m) driven by the laser to accelerate the electrons and (2) Direct or Vacuum Laser Acceleration (DLA or VLA)[18,19,20,21,22,23,24,25,26,27,28] where the injected electrons are directly accelerated by the intense laser field (>10 TV/m). We demonstrate VLA of electrons up to 20 MeV using a qualitatively different injection method that exploits the plasma relativistic transparency (RT) effect38––where dense opaque plasma becomes transparent to the driving laser due to relativistic electron mass increase––by driving a thin solid foil at normal laser incidence

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Conclusion