Continuously tunable narrowband pulses in the THz gap from laser-modulated electron bunches in a storage ring

P Ungelenk,C Mai,S Khan,S Bielawski,A Meyer Auf Der Heide,H Huck,C Szwaj,C Evain,M Höner

doi:10.1103/physrevaccelbeams.20.020706

Abstract

This article reports on the generation of narrowband coherent synchrotron radiation from an electron storage ring. For the first time, this kind of radiation was now produced with continuously tunable frequencies in the so-called “THz gap” (between 1.2 and 5.6 THz), whereas previous experiments were limited to below 750 GHz. The experiment was performed at the DELTA storage ring in Dortmund, Germany, employing the interaction of external intensity-modulated laser pulses with an electron bunch, which causes a periodic longitudinal modulation of the charge density on a sub-millimeter scale. Furthermore, a strong influence of third-order dispersion in the laser pulses on the bandwidth and peak intensity of the THz radiation was observed. This effect is discussed in detail based on numerical simulations of the laser pulse generation and laser-electron interaction, and a modification of the laser system for compensating third-order dispersion is proposed.

Highlights

Coherent synchrotron radiation (CSR) pulses in the terahertz (THz) regime have become of increasing interest for the study of beam dynamics and instabilities in electron storage rings as well as for a growing number of user applications, since the power of CSR exceeds the power of incoherent synchrotron radiation by several orders of magnitude
Since 2011, a short-pulse facility for ultrashort and coherent VUV and THz pulses based on the coherent harmonic generation (CHG) principle has been established at DELTA [18,41,42]
Resulting from the different dispersive properties of the DELTA storage ring, continuously tunable narrowband CSR was generated for the first time at up to 5.6 THz, which is an increase in frequency by a factor of about 10 compared to previous similar experiments

Summary

Introduction

Coherent synchrotron radiation (CSR) pulses in the terahertz (THz) regime have become of increasing interest for the study of beam dynamics and instabilities in electron storage rings (e.g., see [1,2]) as well as for a growing number of user applications (e.g., see [3,4,5,6]), since the power of CSR exceeds the power of incoherent synchrotron radiation by several orders of magnitude. CSR in the THz regime occurs when sub-picosecond structures are present in the longitudinal electron distribution, allowing the electromagnetic waves generated by single electrons to add up constructively at sub-millimeter wavelengths. Broadband CSR pulses in the THz regime were first observed as spontaneous radiation bursts (e.g., see [7,8,9,10]) due to the microbunching instability [11,12]. When the bunch length is reduced to a few picoseconds, e.g., during low-α operation, stable broadband CSR emission in the 100-GHz regime is achieved (e.g., see [13])

Methods

Results

Conclusion