Photon diagnostics at the FLASH THz beamline.

Bertram Green,Ekaterina Zapolnova,Nikola Stojanovic,Vivek Asgekar,Torsten Golz,Gianluca Geloni,Andrea Perucchi,Evgeny Schneidmiller,Michael Gensch,Mihailo D Rabasovic,Jovana Petrovic,Franz Tavella,Aleksandar J Krmpot,Mikhail Yurkov,Sergey Kovalev,Rui Pan,Takanori Tanikawa,Bart Faatz

doi:10.1107/s1600577519003412

Abstract

The THz beamline at FLASH, DESY, provides both tunable (1-300 THz) narrow-bandwidth (∼10%) and broad-bandwidth intense (up to 150 uJ) THz pulses delivered in 1 MHz bursts and naturally synchronized with free-electron laser X-ray pulses. Combination of these pulses, along with the auxiliary NIR and VIS ultrashort lasers, supports a plethora of dynamic investigations in physics, material science and biology. The unique features of the FLASH THz pulses and the accelerator source, however, bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles. Here, these challenges are discussed and the pulse diagnostic tools developed at FLASH are presented. In particular, a radiometric power measurement is presented that enables the derivation of the average pulse energy within a pulse burst across the spectral range, jitter-corrected electro-optical sampling for the full spectro-temporal pulse characterization, spatial beam profiling along the beam transport line and at the sample, and a lamellar grating based Fourier transform infrared spectrometer for the on-line assessment of the average THz pulse spectra. Corresponding measurement results provide a comprehensive insight into the THz beamline capabilities.

Highlights

FLASH, the free-electron laser (FEL) in Hamburg at DESY, provides ultrafast XUV and soft X-ray radiation for users to perform pump–probe experiments
The THz beamline at FLASH, DESY, provides both tunable (1–300 THz) narrow-bandwidth ($ 10%) and broad-bandwidth intense THz pulses delivered in 1 MHz bursts and naturally synchronized with free-electron laser X-ray pulses
We split a small portion of pulse structure is not necessary, we have developed the the beam for a reference measurement that is used to variation of the Fourier transform infrared (FTIR) spectrometer based on a reflective lamellar grating

Summary

Introduction

FLASH, the free-electron laser (FEL) in Hamburg at DESY, provides ultrafast XUV and soft X-ray radiation for users to perform pump–probe experiments. Combined edge and bending dump magnet the THz beamline downstream (estimated to be 11.4%), as radiation can reach a pulse energy of over 10 mJ. The THz beam can be delivered to the into the experimental hall over $ 70 m requires multiple collimations and this is provided by all-reflective optics By this unique photon generation scheme, the photon spectrum experiment via two branches, a short one with ultra-highvacuum transport (10À9 mbar) and a long one via THz diagnostics hutch with high-vacuum transport (10À7 mbar). The shaded area represents the range where the fundamental frequency of the THz undulator radiation can be reached for FLASH1 as a function of the FEL XUV wavelength (lower horizontal axis) and the electron beam energy in the linac (upper horizontal axis). The first experiments performed at FLASH have focused on driving the magnetization dynamics in magnetic thin films by selective phonon excitation (Radu, 2019) and on the THz control of dynamic surface processes (Waltar et al, 2018)

THz power measurement

THz diagnostics

THz temporal profile measurements

THz beam profile

Conclusion

Funding information