All-optical structuring of laser-driven proton beam profiles

Lieselotte Obst-Huebl,João Branco,Jongjin B Kim,Arie Irman,Christian Roedel,Martin Rehwald,Hans-Peter Schlenvoigt,C B Curry ,Michael Bußmann ,M Gauthier ,T Kluge ,U Schramm ,Frederico Fiúza ,Florian‐Emanuel Brack ,Stephan Kraft ,S Göde ,S H Glenzer ,T E Cowan ,Marco Garten,Tim Ziegler,Irene Prencipe,Richard Pausch,Axel Huebl,Josefine Metzkes-Ng,Florian Kroll,Karl Zeil

doi:10.1038/s41467-018-07756-z

Abstract

Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics. Yet, direct control of the proton beam profile is usually not possible. Here we present a readily applicable all-optical approach to imprint detailed spatial information from the driving laser pulse onto the proton bunch. In a series of experiments, counter-intuitively, the spatial profile of the energetic proton bunch was found to exhibit identical structures as the fraction of the laser pulse passing around a target of limited size. Such information transfer between the laser pulse and the naturally delayed proton bunch is attributed to the formation of quasi-static electric fields in the beam path by ionization of residual gas. Essentially acting as a programmable memory, these fields provide access to a higher level of proton beam manipulation.

Highlights

Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics
We report on an all-optical concept to modulate the profile of a multi-MeV proton beam with a single laser pulse by imprinting spatial intensity modulations of the laser onto the proton bunch, without significantly compromising the overall acceleration performance
Field maps induced by the target normal sheath acceleration (TNSA) drive laser itself in the residual gas of the interaction chamber are inscribed on the TNSA protons, as they probe these fields in a proton-radiography-like manner

Summary

Introduction

Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics. Laseraccelerated proton bunches travel at velocities that are a fraction of the speed of light, which inherently precludes temporal overlap with the transmitted drive laser pulse when propagating away from the target This breach of causality represents the second obstacle for an explanation of the measured proton features based on sheath field properties. Induced by ionization of residual gas molecules through the transmitted laser pulse up to >10 mm distances from the laser focus, these fields remain intact for tens of picoseconds, thereby serving as a memorizing structure to bridge the temporal gap until the arrival of protons that were accelerated at the target by TNSA-fields originating from the very same laser pulse A dedicated experiment and particle-in-cell (PIC) simulations are presented to validate the proposed scheme

Methods

Results

Conclusion