Currently, development of compact coherent soft X-ray sources is of particular interest, as they open up a number of important technological and scientific applications. High-harmonic generation in noble gases represents the only way for routinely producing such radiation by compact tabletop lasers in the laboratories worldwide. Coherent ultrashort-pulse X-ray sources based on high-harmonic generation are used to examine layered samples (including microelectronic components) with ultrahigh resolution, follow light-induced chemical reactions via time-resolved X-ray absorption spectroscopy and produce attosecond pulses. The latter are of high demand for problems of extreme laser fields (up to Schwinger limit) and nuclear photonics with the potential to refine existing theoretical models of quantum electrodynamics and develop new approaches.

In this paper we present high-harmonic generation based on a compact source of coherent X-ray radiation developed at Lomonosov Moscow State University. It is utilizing Cr:Forsterite laser technology, which is favored for high-harmonic generation due to the square scaling of the cutoff frequency versus laser wavelength. Soft X-ray pulses in the range of 45-83 eV (27.6–14.9 nm, Fig.1) with a total photon flux of 1.1·10⁹ photons/s were obtained, using an argon gas jet. Optimization of the harmonic flux along with the soft X-ray beam divergence was performed by introducing a frequency chirp into the pump pulse. We believe that the developed compact bright X-ray source represent the first experimental step towards generation of attosecond laser pulses in Russian Federation and can be integrated into rapidly developing domestic free-electron lasers and synchrotron sources in order to increase their temporal coherence.

Fig.1.Generated harmonic spectrum.

Rumiantsev B, Migal’ E., Lobushkin E., Pushkin A., Potemkin F.

JETP Letters 121, issue 5 (2025)