Saturable absorption of intense hard X-rays in iron

Abstract

In 1913, Maurice de Broglie discovered the presence of X-ray absorption bands of silver and bromine in photographic emulsion. Over the following century, X-ray absorption spectroscopy was established as a standard basis for element analysis, and further applied to advanced investigation of the structures and electronic states of complex materials. Here we show the first observation of an X-ray-induced change of absorption spectra of the iron K-edge for 7.1-keV ultra-brilliant X-ray free-electron laser pulses with an extreme intensity of 10(20) W cm(-2). The highly excited state yields a shift of the absorption edge and an increase of transparency by a factor of 10 with an improvement of the phase front of the transmitted X-rays. This finding, the saturable absorption of hard X-rays, opens a promising path for future innovations of X-ray science by enabling novel attosecond active optics, such as lasing and dynamical spatiotemporal control of X-rays.

State-Population Narrowing Effect in Two-Photon Absorption for Intense Hard X-ray Pulses

“…The atomic state response and state populations no longer follow the incident photon pulse profile, and therefore cannot be evaluated with a simple Gaussian-like approximation. Indeed, the saturation of absorption effects were reported for metallic Fe at X-ray flux intensities of 8.4 × 10 34 photons/cm 2 ·s [16]. At the present point, the studies of such effects need more theoretical investigation, as well as experimental verifications.…”

“…As can be seen in Figure 4, for incident X-ray fluxes above 10 32 photons/cm 2 s, both time profiles for these states become wider, however the ratio of their widths remains constant and is equal to about 1.4. The observed increase in the width for the OPA and TPA processes may be considered as a first indication that the saturation regime for nonlinear interaction is approached [15,16]. The atomic state response and state populations no longer follow the incident photon pulse profile, and therefore cannot be evaluated with a simple Gaussian-like approximation.…”

Relativistic ionization dynamics for a hydrogen atom exposed to superintense XUV laser pulses

“…[2,3]). With the latest generation of free electron lasers (European X-Ray Free-Electron Laser, SPring-8 Angstrom Compact Free Electron Laser, Linac Coherent Light Source), an unprecedented brilliance in the extreme ultraviolet (XUV) region and beyond is reached, and new techniques [4] to focus the beam, as well as preliminary results [5], promise intensities also in this wavelength region exceeding 10 20 W/cm 2 . The treatment of light-matter interaction in a relativistic framework is thus a timely issue.…”

X-ray free-electron laser studies of dense plasmas

“…It follows that rather than an exception, saturable absorption is a characteristic phenomenon of high-intensity FEL interactions with matter. Experimentally it has now been observed in multiple systems and over a range of different conditions, both at the Linac Coherent Light Source (LCLS) X-ray FEL in California Young et al 2010;Rackstraw et al 2015) and on the Japanese X-ray FEL SACLA (Yoneda et al 2014). …”