Single-shot spectro-temporal characterization of XUV pulses from a seeded free-electron laser.

Giovanni De Ninno,Eugenio Ferrari,Luca Giannessi,Paolo Sigalotti,Giuseppe Penco,David Gauthier,Matija Stupar,Paolo Cinquegrana,Benoît Mahieu,Alexander Demidovich,Enrico Allaria,Primož Rebernik Ribič,Miltcho Bojanov Danailov

doi:10.1038/ncomms9075

Abstract

Intense ultrashort X-ray pulses produced by modern free-electron lasers (FELs) allow one to probe biological systems, inorganic materials and molecular reaction dynamics with nanoscale spatial and femtoscale temporal resolution. These experiments require the knowledge, and possibly the control, of the spectro-temporal content of individual pulses. FELs relying on seeding have the potential to produce spatially and temporally fully coherent pulses. Here we propose and implement an interferometric method, which allows us to carry out the first complete single-shot spectro-temporal characterization of the pulses, generated by an FEL in the extreme ultraviolet spectral range. Moreover, we provide the first direct evidence of the temporal coherence of a seeded FEL working in the extreme ultraviolet spectral range and show the way to control the light generation process to produce Fourier-limited pulses. Experiments are carried out at the FERMI FEL in Trieste.

Highlights

Intense ultrashort X-ray pulses produced by modern free-electron lasers (FELs) allow one to probe biological systems, inorganic materials and molecular reaction dynamics with nanoscale spatial and femtoscale temporal resolution
The availability of ultrashort fully coherent pulses generated by seeded free-electron lasers (FELs)[1,2,3,4,5,6,7,8,9] in the ultraviolet and extreme ultraviolet (XUV) spectral ranges opens the door to completely new experiments of nonlinear optics[10,11]
While spatial coherence is a property of FELs based on self-amplified spontaneous emission[16], the capability of generating temporally coherent pulses is a distinctive feature of seeded FELs

Summary

Introduction

Intense ultrashort X-ray pulses produced by modern free-electron lasers (FELs) allow one to probe biological systems, inorganic materials and molecular reaction dynamics with nanoscale spatial and femtoscale temporal resolution. A curvature d2E(t)/dt[2] in the electron energy E(t) produces the same effect as a linear frequency chirp in the seed[18,19,20] and causes an additional linear frequency offset during amplification due to varying dE(t)/dt along the electron beam[21] As shown below, such an offset plays a key role in the method we have implemented for the reconstruction of the FEL pulse. Our results demonstrate the possibility to take advantage of the interplay between the seed and electron-energy chirps to generate Fourier-limited pulses, that is, pulses with the minimum possible time–bandwidth product

Methods

Results

Conclusion