The time–energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s ...photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.
The X-ray free-electron laser has opened a new era for photon science, improving the X-ray brightness by ten orders of magnitude over previously available sources. Similar to an optical laser, the ...spectral and temporal structure of the radiation pulses can be tailored to the specific needs of many experiments by accurately manipulating the lasing medium, that is, the electron beam. Here we report the generation of mJ-level two-colour hard X-ray pulses of few femtoseconds duration with an XFEL driven by twin electron bunches at the Linac Coherent Light Source. This performance represents an improvement of over an order of magnitude in peak power over state-of-the-art two-colour XFELs. The unprecedented intensity and temporal coherence of this new two-colour X-ray free-electron laser enable an entirely new set of scientific applications, ranging from X-ray pump/X-ray probe experiments to the imaging of complex biological samples with multiple wavelength anomalous dispersion.
Population inversion X-ray laser oscillator Halavanau, Aliaksei; Benediktovitch, Andrei; Lutman, Alberto A. ...
Proceedings of the National Academy of Sciences - PNAS,
07/2020, Letnik:
117, Številka:
27
Journal Article
Recenzirano
Odprti dostop
Oscillators are at the heart of optical lasers, providing stable, transform-limited pulses. Until now, laser oscillators have been available only in the infrared to visible and near-ultraviolet (UV) ...spectral region. In this paper, we present a study of an oscillator operating in the 5- to 12-keV photon-energy range. We show that, using the Kα₁ line of transition metal compounds as the gain medium, an X-ray free-electron laser as a periodic pump, and a Bragg crystal optical cavity, it is possible to build X-ray oscillators producing intense, fully coherent, transform-limited pulses. As an example, we consider the case of a copper nitrate gain medium generating ∼ 5 × 1010 photons per pulse with 37-fs pulse length and 48-meV spectral resolution at 8-keV photon energy. Our theoretical study and simulation of this system show that, because of the very large gain per pass, the oscillator saturates and reaches full coherence in four to six optical-cavity transits. We discuss the feasibility and design of the X-ray optical cavity and other parts of the oscillator needed for its realization, opening the way to extend X-ray–based research beyond current capabilities.
X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device ...called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500-1,200eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98 sub(-0.04) super(+0.02) at 707eV and may be scanned in energy. We also present a new two-colour X-ray pump-X-ray probe operating mode for the LCLS. Energy differences of Delta E/E=2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified.
Polarization control is a key feature of light generated by short-wavelength free-electron lasers. In this work, we report the first experimental characterization of the polarization properties of an ...extreme ultraviolet high gain free-electron laser operated with crossed polarized undulators. We investigate the average degree of polarization and the shot-to-shot stability and we analyze aspects such as existing possibilities for controlling and switching the polarization state of the emitted light. The results are in agreement with predictions based on Gaussian beams propagation.
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