Resonant phase matching by oblique illumination of a dielectric laser accelerator

S Crisp,P Musumeci,R J England,A Ody

doi:10.1103/physrevaccelbeams.24.121305

Abstract

In dielectric laser-driven accelerators (DLA), careful tuning of drive-laser wavelength and structure periodicity is typically required in order to hit the resonant condition and match the phase velocity of the accelerating wave to the electron beam velocity. By aggressively detuning (up to 30 mrad) the angle of incidence of the drive laser on a double grating DLA structure, we show that it is possible to recover resonant phase matching and maximize the energy modulation of an externally injected 6 MeV beam in a 800 nm period structure driven using a 780 nm laser. These results show that it is possible to power DLA structures away from their design working point, and excite accelerating fields in the gap with phase profiles that change by a relatively large amount period-to-period. This flexibility is a key feature of DLAs and a critical element in the realization of phase-modulation based ponderomotive focusing to demonstrate MeV energy gain and large capture in a single DLA stage.

Highlights

Dielectric laser accelerators (DLA) hold the promise to shrink the size of relativistic particle accelerators by four orders of magnitude due to their micron-size characteristic scales, while at the same time increasing the accelerating gradient by more than one order of magnitude [1,2,3,4]
One important characteristic of DLAs is the temporal format of the output beams which are microbunched on the scale of the laser wavelength [13,14]
While optically microbunched beams have been demonstrated in various setups ranging from high-energy particle accelerator beamlines [15,16] to electron microscope columns [17], DLAs offer unique advantages toward solving the problem of coupling infrared and visible light to moderately relativistic

Summary

INTRODUCTION

Dielectric laser accelerators (DLA) hold the promise to shrink the size of relativistic particle accelerators by four orders of magnitude due to their micron-size characteristic scales, while at the same time increasing the accelerating gradient by more than one order of magnitude [1,2,3,4]. From the fabrication point of view, manufacturing limitations often constrain the physical dimensions of the DLA features to nonoptimized (typically larger) sizes so that driving a structure with a different laser wavelength might even yield improvements in the diffraction efficiency All these cases indicate that the possibility to compensate in situ for structure mismatch could be an important factor in large scale DLA development. If illuminated at normal incidence, the phase velocity in these structures would be larger than c and not suitable for particle acceleration, but by varying the incident angle from the normal by as much as 30 mrad, resonance with relativistic electrons is recovered and the energy modulation maximized These results provide an experimental validation of the wide acceptance bandwidth of DLA structures, confirming that is possible to have large phase shifts in adjacent periods of the DLA [24,25]. The significance of these results is discussed before drawing general conclusions

EXPERIMENTAL SETUP

ANALYSIS OF SPECTROMETER IMAGES TO RETRIEVE MAXIMUM ENERGY MODULATION

Findings

CONCLUSION