Caustic structures in x-ray Compton scattering off electrons driven by a short intense laser pulse

D Seipt,A Surzhykov,B Kämpfer,S Fritzsche

doi:10.1088/1367-2630/18/2/023044

Abstract

We study the Compton scattering of x-rays off electrons that are driven by a relativistically intense short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a broad plateau in the vicinity of the laser-free Compton line due to a nonlinear mixing between x-ray and laser photons. Special emphasis is placed on how the shape of the short assisting laser pulse affects the spectrum of the scattered x-rays. In particular, we observe sharp peak structures in the plateau region, whose number and locations are highly sensitive to the laser pulse shape. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element, relating the caustic peak locations to the laser-driven electron motion.

Highlights

X-ray free electron lasers (XFELs) help explore matter on ultra-short time-scales and under extreme conditions
The x-ray scattering off dense plasmas—for instance those plasmas generated by irradiating a solid density target with an ultra-intense optical laser pulse [3] —facilitate the study of ultra-fast collective dynamics and plasma instabilities [4,5,6,7], which are important for novel particle acceleration [8,9,10] or fusion energy concepts [3], for instance
We present a quantum electrodynamics (QED) description of laser assisted Compton scattering [34,35,36,37,38,39] of an ultra-short pulse of coherent x-rays from an XFEL off electrons moving in an intense (a0 ~ 1) and ultra-short synchronised optical laser pulse [40,41,42]

Summary

17 February 2016

We study the Compton scattering of x-rays off electrons that are driven by a relativistically intense author(s) and the title of the work, journal citation short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a and DOI. Special emphasis is placed on how the shape of the short assisting laser pulse affects the spectrum of the scattered x-rays. We observe sharp peak structures in the plateau region, whose number and locations are highly sensitive to the laser pulse shape. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element, relating the caustic peak locations to the laser-driven electron motion

Introduction

Theoretical description: the QED cross section

X a2X h 2

Semiclassical interpretation of the spectral peaks as spectral caustics

Discussion

Summary and conclusions