Significance: An X-ray oscillator generating fully coherent pulses at the characteristic length and time scale of atomic and molecular phenomena, angstrom wavelength, and femtosecond time duration has been a dream of laser physics from the 1960s. The paper presents a study of an X-ray oscillator based on population inversion of K α electrons in a transition-metal compound, generating fully coherent, transform-limited, high-power radiation pulses, in the 3- to <1-Å wavelength region, with a high-energy resolution, about 0.05 eV, showing that the dream can now become a reality. The X-ray laser oscillator will open experimental possibilities and research areas in quantum optics, chemical dynamics, imaging, spectroscopy, and interferometric measurements.

This paper presents a novel cantilevered liquid-nitrogen-cooled silicon mirror design for the first optic in a new soft X-ray beamline that is being developed as part of the Advanced Light Source Upgrade (ALS-U) (Lawrence Berkeley National Laboratory, USA). The beamline is optimized for photon energies between 400 and 1400 eV with full polarization control. Calculations indicate that, without correction, this design will achieve a Strehl ratio greater than 0.85 for the entire energy and polarization ranges of the beamline. With a correction achieved by moving the focus 7.5 mm upstream, the minimum Strehl ratio is 0.99. This design is currently the baseline plan for all new ALS-U insertion device beamlines.

The emergence of X-ray Free Electron Lasers (XFELs) in recent years has opened up new fields of research, with the merging of short wavelengths and ultrafast timescales [1, 2]. As XFEL facilities, ...

FERMI@Elettra is a new free-electron-laser (FEL) facility, presently under commissioning, able to generate subpicosecond photon pulses of high intensity in the far ultraviolet and soft X-ray range (λ=100-20 nm for the present FEL1 source, extended in future to 4 nm with the FEL2 source). Here we briefly describe the present status of the TIMEX end-station, devoted to perform experiments on condensed matter under extreme conditions. The layout of the end-station, presently in the final stages of construction, is reported showing the details of the optics and sample environment. The potential for transmission, reflection, scattering, as well as pump-and-probe experiments is discussed taking into account that FEL pulses can heat thin samples up to the warm dense matter (WDM) regime. The calculated deposited energy in selected elemental films, including saturation effects, shows that homogeneous heating up to very high temperatures (1-10 eV for the electrons) can be easily reached with a suitable tuning of the energy and focus of the soft x-ray pulses of FERMI@Elettra. The results of the first test of the TIMEX end-station are also reported.