Compact high-repetition-rate source of coherent 100 eV radiation

Abstract

Coherently enhancing laser pulses in a passive cavity provides ideal conditions for high-order harmonic generation in a gas, with repetition rates around 100 MHz (refs 1,2,3). Recently, extreme-ultraviolet radiation with photon energies of up to 30 eV was obtained, which is sufficiently bright for direct frequency-comb spectroscopy at 20 eV (ref. 4). Here, we identify a route to scaling these radiation sources to higher photon energies. We demonstrate that the ionization-limited attainable intracavity peak intensity increases with decreasing pulse duration. By enhancing nonlinearly compressed pulses of an Yb-based laser and coupling out the harmonics through a pierced cavity mirror, we generate spatially coherent 108 eV (11.45 nm) radiation at 78 MHz. Exploiting the full potential of the demonstrated techniques will afford high-photon-flux ultrashort-pulsed extreme-ultraviolet sources for a number of applications in science and technology, including photoelectron spectroscopy, coincidence spectroscopy with femtosecond to attosecond resolution and characterization of components and materials for nanolithography

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

“…This results in a conversion efficiency of 6.7 3 10 27 , enabling more than 50 mW in a single harmonic (.10 13 photons s -1 ), which is an improvement of four orders of magnitude compared with the reported multi-MHz systems of a single-pass HHG 28,29 . The photon flux is not only higher than what is supplied by current Ti:Sapphire technology 30 but also higher than intra-cavity HHG in the same wavelength range 8,24,31 . Additionally, the demonstrated repetition rate has previously been only accessible with enhancement cavities 23 .…”

“…The achieved photon flux is four orders of magnitude larger than that reported in studies on multi-MHz repetition rate HHG directly driven with a laser, i.e., without the additional enhancement cavity 28,29 . Moreover, the flux obtained in H23 is higher than what the state-of-the art enhancement cavities can deliver 8,24,31 and also exceeds the currently used kHz systems 30 .…”

“…This laser system is used to demonstrate transiently phase-matched HHG. More than 10 13 photons s -1 (.50 mW) are achieved in a single harmonic at 27.7 eV, which is an improvement of four orders of magnitude for a directly driven multiMHz repetition rate HHG 28,29 , and it provides a photon flux that is higher than that delivered by standard kHz laser systems 30 and intracavity HHG within that wavelength range 8,24,31 . The use of a lowenergy driving laser with a compact nonlinear compression setup not only has the potential to significantly reduce the complexity of high repetition rate HHG systems but will also enable efficient HHG at 10 MHz repetition rate, a regime so far only addressable with enhancement cavities.…”

“…Moreover, the harmonics have to be generated directly in the resonator, which necessitates an out-coupling mechanism for the harmonics, adding additional experimental complexity 8,24 . The occurring ionization of the generation gas puts further constraints on the achievable enhancement and phase-matching conditions that challenges further development 24,25 . A second approach relies on plasmonic field enhancement that potentially allows operation directly with laser oscillators 26 .…”

A concept for multiterawatt fibre lasers based on coherent pulse stacking in passive cavities

“…Recently, with an enhancement factor of 2000, 10 ps pulses were enhanced to 670 kW of intracavity average power. 31 So far, these systems are mainly used for the generation of short-wavelength radiation via intracavity high-harmonic generation [31][32][33][34] or inverse Compton scattering. 35 The SnD concept employs an enhancement cavity for coherent pulse stacking.…”