Double-grating monochromatic beamline with ultrafast response for FLASH2 at DESY.

Günter Brenner,Marion Kuhlmann,Fabio Frassetto,Elke Plönjes,Luca Poletto

doi:10.1107/s1600577517013777

Abstract

The preliminary design of a monochromatic beamline for FLASH2 at DESY is presented. The monochromator is tunable in the 50-1000 eV energy range with resolving power higher than 1000 and temporal response below 50 fs over the whole energy range. A time-delay-compensated configuration using the variable-line-spacing monochromator design with two gratings is adopted: the first grating disperses the radiation on its output plane, where the intermediate slit performs the spectral selection; the second grating compensates for the pulse-front tilt and for the spectral dispersion due to diffraction from the first grating.

Highlights

Free-electron laser (FEL) sources provide extreme-ultraviolet (XUV) and X-ray radiation with ultrashort time duration, high spatial coherence and an increase of six to eight orders of magnitude on the peak brilliance with respect to synchrotron radiation sources (Huang & Kim, 2007)
This paper is focused on the monochromatization of FEL pulses to go beyond the intrinsic resolution of self-amplified spontaneous emission (SASE) FELs
We present the preliminary design of a monochromator beamline for FLASH2 at DESY (Faatz et al, 2016; Plonjes et al, 2016)

Summary

Introduction

In the following we will concentrate on the double-grating configuration applied to the VLS grating monochromator. The decrease of the initial pulse length of the FEL pulse This is the value to be resolving power is almost negligible even for 2 mrad r.m.s. compared with the Fourier limit and with the group delay slope errors on the optics. The the spot size at the output, the degradation being almost a results reported in Fig. 7 show that for wavelengths shorter factor of two for 2 mrad r.m.s. slope errors This is the main than 7 nm the group delay is the dominating factor limiting the effect to be considered when defining the desired quality of pulse duration for a Fourier-limited pulse in the 15–25 fs the optical surfaces. The experimental chamber have to be moved to the new focal position for experiments at short wavelengths: the required rotation is 6 and the resulting (horizontal) translation is $ 20 cm for the KB system and $ 40 cm for the experimental chamber in the proposed design

Single-grating monochromator for ultrafast pulses

Conclusions