Exploring new avenues in high repetition rate table-top coherent extreme ultraviolet sources

The process of high harmonic generation(HHG)enables the development of table-top sources of coherent extreme ultraviolet(XUV)light.Although these are now matured sources,they still mostly rely on bulk laser technology that limits the attainable repetition rate to the low kilohertz regime.Moreover,many of the emerging applications of such light sources(e.g.,photoelectron spectroscopy and microscopy,coherent diffractive imaging,or frequency metrology in the XUV spectral region)require an increase in the repetition rate.Ideally,these sources are operated with a multi-MHz repetition rate and deliver a high photon flux simultaneously.So far,this regime has been solely addressed using passive enhancement cavities together with low energy and high repetition rate lasers.Here,a novel route with significantly reduced complexity(omitting the requirement of an external actively stabilized resonator)is demonstrated that achieves the previously mentioned demanding parameters.A krypton-filled Kagome photonic crystal fiber is used for efficient nonlinear compression of 9 μJ,250 fs pulses leading to,7 μJ,31 fs pulses at 10.7 MHz repetition rate.The compressed pulses are used for HHG in a gas jet.Particular attention is devoted to achieving phase-matched(transiently)generation yielding.10^(13) photons s^(-1)(.50 μW)at 27.7 eV.This new spatially coherent XUV source improved the photon flux by four orders of magnitude for direct multi-MHZ experiments,thus demonstrating the considerable potential of this source.

Material-specific high-resolution table-top extreme ultraviolet microscopy

Microscopy with extreme ultraviolet(EUV)radiation holds promise for high-resolution imaging with excellent material contrast,due to the short wavelength and numerous element-specific absorption edges available in this spectral range.At the same time,EUV radiation has significantly larger penetration depths than electrons.It thus enables a nano-scale view into complex three-dimensional structures that are important for material science,semiconductor metrology,and next-generation nano-devices.Here,we present high-resolution and material-specific microscopy at 13.5 nm wavelength.We combine a highly stable,high photon-flux,table-top EUV source with an interferometrically stabilized ptychography setup.By utilizing structured EUV illumination,we overcome the limitations of conventional EUV focusing optics and demonstrate high-resolution microscopy at a half-pitch lateral resolution of 16 nm.Moreover,we propose mixed-state orthogonal probe relaxation ptychography,enabling robust phase-contrast imaging over wide fields of view and long acquisition times.In this way,the complex transmission of an integrated circuit is precisely reconstructed,allowing for the classification of the material composition of mesoscopic semiconductor systems.