Novel method for the generation of stable radiation from free-electron lasers at high repetition rates

Sven Ackermann,Wolfgang Hillert,Mehdi Mohammad Kazemi,Svitozar Serkez,Christoph Lechner,Gianluca Geloni,Bart Faatz,Johann Zemella,Tino Lang,Georgia Paraskaki,Takanori Tanikawa,Vanessa Grattoni

doi:10.1103/physrevaccelbeams.23.071302

Abstract

For more than a decade free-electron lasers (FELs) have been in operation, providing scientists from many disciplines with the benefits of ultrashort, nearly transversely coherent radiation pulses with wavelengths down to the \AA{}ngstrom range. If no further techniques are applied, the FEL will only amplify radiation from the stochastic distributed electron density in the electron bunch. Contemporary developments aim at producing stable and single-mode radiation by preparing an electron bunch with favorable longitudinal electron density distributions using magnets and conventional laser pulses (seed), hence the name ``seeding.'' In recent years, short wavelength FELs at high electron beam energies and high repetition rates were proposed and built. At those repetition rates, an external seed with sufficient power to manipulate the electron beam cannot be provided by present state-of-the-art laser systems, thus no external seeding scheme could be applied yet. In this paper, we present ways to seed FELs to generate short wavelength radiation at high repetition rates, making use of tested electron beam manipulation schemes. For our parameter study, we used the parameters of FLASH, the free-electron laser in Hamburg. First simulations are presented, showing the feasibility of the method proposed.

Highlights

In most free-electron lasers (FELs), the radiation generation process referred to as self-amplified spontaneous emission (SASE) radiation is initiated only by the stochastic noise in the electron density distribution in the bunch, called shot noise
This covers a significant number of FEL facilities, there is a trend toward shorter wavelengths and high repetition rates
The simulations performed in IV support the assumption that an optical feedback based FEL can work in principle, and state-of-the-art optical components to build such optical feedback system do already exist

Summary

INTRODUCTION

In most free-electron lasers (FELs), the radiation generation process referred to as self-amplified spontaneous emission (SASE) radiation is initiated only by the stochastic noise in the electron density distribution in the bunch, called shot noise. All studies mentioned above have in common that the application of seeding techniques was not investigated Another idea is to use the spent electron beam just before it is dumped to generate radiation which is stored in an oscillator. Choosing the right modulator length and initial seed laser power for a given wavelength can keep the induced energy spread in the modulator controlled, and far from saturation. V will summarize the work and give an outlook onto further studies to come

ACHIEVING HIGH REPETITION RATES

ACHIEVING SHORT WAVELENGTHS AT HIGH REPETITION RATES

Echo-enabled harmonic generation

FIRST MULTIPASS HGHG SIMULATIONS

Summary