Abstract

High harmonic generation (HHG) enables coherent extreme-ultraviolet (XUV) radiation with ultra-short pulse duration in a table-top setup. This has already enabled a plethora of applications. Nearly all of these applications would benefit from a high photon flux to increase the signal-to-noise ratio and decrease measurement times. In addition, shortest pulses are desired to investigate fastest dynamics in fields as diverse as physics, biology, chemistry and material sciences. In this work, the up-to-date most powerful table-top XUV source with 12.9 ± 3.9 mW in a single harmonic line at 26.5 eV is demonstrated via HHG of a frequency-doubled and post-compressed fibre laser. At the same time the spectrum supports a Fourier-limited pulse duration of sub-6 fs in the XUV, which allows accessing ultrafast dynamics with an order of magnitude higher photon flux than previously demonstrated. This concept will greatly advance and facilitate applications of XUV radiation in science and technology and enable photon-hungry ultrafast studies.

Highlights

  • Since the first experimental demonstration of high harmonic generation in the late 1980s [1, 2], strong efforts have been made to enhance the average power of laser-like sources in the Extreme ultraviolet (XUV) [3], enabling applications on the atomic length-(nanometer) [4] and time-scale [5, 6]

  • A spatial characterization of this compressed beam shows a nearly diffraction limited beam quality with an M2 value of 1.25 × 1.26. This unique combination of short wavelength, ultrashort pulse duration, high average power and very good beam quality represents a novel class of driving laser for high harmonic generation at a five-fold higher average power compared to previous results [33, 34]

  • The spectrum supports a Fourier limited pulse duration of 3.4 fs and simulation results suggest that the time span of the efficient high harmonic generation is shorter than 6 fs

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Summary

Introduction

Since the first experimental demonstration of high harmonic generation in the late 1980s [1, 2], strong efforts have been made to enhance the average power of laser-like sources in the XUV [3], enabling applications on the atomic length-(nanometer) [4] and time-scale (femtosecond to attosecond) [5, 6]. In the early stages up to the year 2010 (Fig. 1), Ti:Sa based amplifiers have been proven as an effective driver for HHG [3, 7, 8], since they provide ultra-short pulse durations (~ 25 fs) at 800 nm wavelength and high pulse energies (several millijoule). Their limited average power of a few tens of watts in best case [16], limited the XUV flux of such systems to sub100 μW per harmonic line (Fig. 1). The latter ones made use of the efficiency scaling of the single atom response with λ6, where λ represents the driving wavelength [29], increasing the HHG efficiency by more than one order of magnitude

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