Generation of Coherent sub-20 nm XUV Radiation at 78 MHz via Cavity-Based HHG

I Pupeza,J Limpert,P Rußbüldt,Th Udem,H Carstens,F Krausz,S Holzberger,A Tünnermann,D Esser,T.W Hänsch,E Fill,T Eidam,J Weitenberg,M Chergui,R De Vivie-Riedle,S Cundiff,A Taylor,K Yamagouchi

doi:10.1051/epjconf/20134110023

Abstract

We present two major advances of enhancement-cavity-based high-order har- monic generation (HHG). First, the generated extreme ultraviolet (XUV) radiation is cou- pled out collinearly through an on-axis opening in the mirror following the HHG focus. This minimizes the interaction of both the fundamental and the intracavity generated ra- diation with the output coupler while simultaneously enabling a large enhancement and an output coupling efficiency that increases with the harmonic order. Second, we use the nonlinearly compressed pulses of an Yb-based laser to drive intracavity HHG allowing for a unique power regime combining short pulses with high average powers. Together, these advances overcome fundamental limitations of current enhancement cavity setups and extend intracavity HHG towards higher photon energies. In a proof-of-principle ex- periment we use a 3-kW and 78-MHz train of 54-fs to generate and couple out coherent sub-20 nm radiation.

Highlights

In all high-order harmonic generation (HHG)-enhancement cavity (EC) the spatial separation of the generated harmonic radiation from the fundamental beam and, coupling out of the XUV relies on reflection or diffraction, precluding a performance scaling of these concepts towards significantly higher photon energies
XUV output coupling through an on-axis opening in the mirror following the focus minimizes the interaction of both the fundamental and the generated radiation with the output coupler (OC) while simultaneously allowing for a large enhancement and output coupling efficiency
The hole-OC allows for the first time efficient photon-energy-scalable collinear XUV output coupling without introducing additional dispersion, nonlinearities or polarization discrimination for the fundamental radiation

Summary

Introduction

In all HHG-ECs the spatial separation of the generated harmonic radiation from the fundamental beam and, coupling out of the XUV relies on reflection or diffraction, precluding a performance scaling of these concepts towards significantly higher photon energies. In this contribution we present two major advances in the femtosecond EC technology. Sub-100 fs pulses are enhanced to several kW of average power and the generation of sub-20nm coherent radiation with the Gaussian fundamental transverse mode of a resonator is demonstrated This concept is simultaneously scalable towards higher generated photon energy and photon flux and towards shorter pulses

Experimental Setup and Results

Findings

Conclusions and Outlook