Ultrafast MHz‐Rate Burst‐Mode Pump–Probe Laser for the FLASH FEL Facility Based on Nonlinear Compression of ps‐Level Pulses from an Yb‐Amplifier Chain

Marcus Seidel,Nils Wind,John Darvill,Thomas Binhammer,Federico Pressacco,Dmytro Kutnyakhov,Ingmar Hartl,Henrik Tünnermann,Nora Schirmel,Hamed Tavakol,Uwe Grosse‐Wortmann,Nagitha Ekanayake,Christian Mohr,Bastian Manschwetus,Lukas Wenthaus,Chen Li,Christoph M Heyl,Sebastian Schulz,Jost Müller,Michael Heber,Oender Akcaalan,H Redlin ,A Swiderski ,O Puncken ,C Vidoli ,M Frede ,L Winkelmann

doi:10.1002/lpor.202100268

Abstract

AbstractThe Free‐Electron Laser (FEL) FLASH offers the worldwide still unique capability to study ultrafast processes with high‐flux, high‐repetition rate extreme ultraviolet, and soft X‐ray pulses. The vast majority of experiments at FLASH are of pump–probe type. Many of them rely on optical ultrafast lasers. Here, a novel FEL facility laser is reported which combines high average power output from Yb:YAG amplifiers with spectral broadening in a Herriott‐type multipass cell and subsequent pulse compression to sub‐100‐fs durations. Compared to other facility lasers employing optical parametric amplification, the new system comes with significantly improved noise figures, compactness, simplicity, and power efficiency. Like FLASH, the optical laser operates with 10‐Hz burst repetition rate. The bursts consist of 800‐μs long trains of up to 800 ultrashort pulses being synchronized to the FEL with femtosecond precision. In the experimental chamber, pulses with up to 50‐μJ energy, 60‐fs full‐width half‐maximum duration and 1‐MHz rate at 1.03‐μm wavelength are available and can be adjusted by computer‐control. Moreover, nonlinear polarization rotation is implemented to improve laser pulse contrast. First cross‐correlation measurements with the FEL at the plane‐grating monochromator photon beamline are demonstrated, exhibiting the suitability of the laser for user experiments at FLASH.

Highlights

The superconducting Free-Electron Laser (FEL) FLASH provides ultrashort, extremely powerful pulses in the XUV and soft X-ray spectral range (1.5 nm to 50 nm) at the highest repetition rates worldwide
It is the first optical laser in FEL beamline user operation which relies on the concept of nonlinear spectral broadening in Herriott-type multipass cells (MPC).[5,6]
The results presented here highlight the attractiveness of the pulse-compression approach for future FEL pump-probe laser developments

Summary

Introduction

The superconducting Free-Electron Laser (FEL) FLASH provides ultrashort, extremely powerful pulses in the XUV and soft X-ray spectral range (1.5 nm to 50 nm) at the highest repetition rates worldwide. At FLASH, the availability of the optical lasers for pump-probe experiments was above 95 % of the requested time over the past 3 years. During the past ten years, two optical lasers were available at the FLASH1 beamlines:[4] First, a Ti:sapphire laser with 10 Hz repetition rate providing mJ-level pulse energies. The previously used, complex OPCPA system was decommissioned in fall 2020 and has been replaced by a much simpler laser system which is reported here It is the first optical laser in FEL beamline user operation which relies on the concept of nonlinear spectral broadening in Herriott-type multipass cells (MPC).[5,6] The method enables compression of high-power pslevel pulses from Yb-based lasers to sub-100 fs duration with a compact setup, very good intraburst pulse energy flatness and excellent burst-to-burst energy stability. It will be an essential ingredient for upcoming cutting-edge FEL experiments

Methods

Findings

Discussion

Conclusion