Generation of bright X-ray radiation in the wavelength range of 15-27 nm under excitation of a gas jet by intense phase-modulated near-infrared femtosecond laser pulses

A source of coherent X-ray radiation based on the high harmonic generation in a gaseous medium has been developed at the Moscow State University. The generation in an argon gas jet irradiated by femtosecond laser radiation of a Cr:forsterite laser system has been carried out for the first time. High harmonic radiation in the photon energy range of 45–83 eV (corresponding wavelengths from 27.6 to 14.9 nm) with a total generated photon flux 1.1 $\times$ 10$^9$ photons/s has been detected under optimal generation conditions. It has been shown that the compensation of self-phase modulation of the generating pulse by introducing negative quadratic phase modulation makes it possible to increase the generation efficiency in a wide range of generated harmonics from the low- to high-frequency plateau edge. It has also been found that such modulation allows one to reduce the divergence of high harmonics at the edge of the plateau and to increase the cutoff frequency. The developed compact bright X-ray source opens the way to obtaining attosecond laser pulses in the Russian Federation, and can also be used to form a coherent seed in free-electron lasers and synchrotron radiation sources in order to increase the temporal coherence of their radiation.