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

Abstract

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 mJ, 250 fs pulses leading to ,7 mJ, 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 mW) 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.

Phase-stable, multi-µJ femtosecond pulses from a repetition-rate tunable Ti:Sa-oscillator-seeded Yb-fiber amplifier

“…The repetition rate of the 0.7-µJ, ~32-fs output pulses can be reduced from 74 MHz (fundamental repetition rate of the oscillator) by an integer factor of up to 4 without affecting the pulse parameters. In principle, the repetition rate can be further reduced at the same average power by stronger pulse stretching in the CPA [31] and the pulse duration can be further compressed with alternative, pulse-energy-scalable schemes [9][10][11][12][13][14]. For all repetition rates, an integrated phase noise of 60-mrad in-loop and 225-mrad out-of-loop was measured in a bandwidth from 2 mHz to 4 kHz.…”

“…The solid-core-fiberbased spectral broadening employed here is limited to around 1-µJ input pulse energy by self-focusing-induced damage in the fiber. This is, however, not a fundamental limitation in view of the recently demonstrated power scalable compression schemes in bulk [9,28] as well as in kagome fibers [14]. The beam profile and autocorrelation traces for the four repetition rates are shown in Fig.…”

“…The superior thermal properties of Yb-doped active media enable an improvement of several orders of magnitude in terms of average power [7][8][9][10][11]. To overcome the disadvantage of a significantly narrower gain bandwidth, several post-amplification nonlinear pulse compression techniques have been developed [9][10][11][12][13][14]. Recently, from an Yb:YAG thin-disk oscillator followed by two nonlinear compression stages, pulses of 2.2 cycles with 6 W of average power at a repetition rate of 38 MHz and with a phase jitter of 270 mrad (out-of-loop phase noise integrated in the band between 1 Hz and 500 kHz) were demonstrated [10].…”

High photon flux and repetition rate table-top EUV sources based on ultrashort pulse fiber lasers

“…Even higher repetition rates can be obtained when using a Kagome photonic crystal fiber for nonlinear compression in a single stage setup [7]. This allows operating the nonlinear compression at energies as low as …”

“…10 9 photons/s at 120 eV, while the spectrum can reach to the water-window [6]. Furthermore, the repetition rate can be increased to 10.7 MHz while maintaining a high photon flux of 10 13 photons/s at 27.7 eV (51I1W) [7].…”