Observation of Seeded Mn Kβ Stimulated X-Ray Emission Using Two-Color X-Ray Free-Electron Laser Pulses

Abstract

Kβ x-ray emission spectroscopy is a powerful probe for electronic structure analysis of 3d transition metal systems and their ultrafast dynamics. Selectively enhancing specific spectral regions would increase this sensitivity and provide fundamentally new insights. Recently we reported the observation and analysis of Kα amplified spontaneous x-ray emission from Mn solutions using an x-ray free-electron laser to create the 1s core-hole population inversion [Kroll et al., Phys. Rev. Lett. 120, 133203 (2018)]. To apply this new approach to the chemically more sensitive but much weaker Kβ x-ray emission lines requires a mechanism to outcompete the dominant amplification of the Kα emission. Here we report the observation of seeded amplified Kβ x-ray emission from a NaMnO 4 solution using two colors of x-ray free-electron laser pulses, one to create the 1s core-hole population inversion and the other to seed the amplified Kβ emission. Comparing the observed seeded amplified Kβ emission signal with that from conventional Kβ emission into the same solid angle, we obtain a signal enhancement of more than 10 5. Our findings are the first important step of enhancing and controlling the emission of selected final states of the Kβ spectrum with applications in chemical and materials science.

XUV superfluorescence from helium gas in the paraxial three-dimensional approximation

“…The angular divergence of the emitted field also varied with increasing gas pressure or pump pulse energy and was calculated to be significantly larger than that of the pump beam. The latter is in line with experimental observation of seeded Mn Kβ emission [16], where field amplification was detected based on the large angular divergence of emitted radiation.…”

“…Modeling the spatial dependence of the emitted field intensity is also crucial for experiments in which the gain cannot be simply inferred from measurements of the emitted pulse energy. Such an example is the observation of seeded Mn Kβ stimulated emission [16], where the target was irradiated with two-color FEL pulses. One color was used to create a core-hole population inversion and the other to stimulate the weak Kβ emission.…”

Using X-ray free-electron lasers for spectroscopy of molecular catalysts and metalloenzymes

“…Seeding of Kβ emission from a NaMnO 4 solution with an enhancement of more than 10 5 compared with spontaneous emission into the same solid angle was reported 140 , with strong spectral narrowing (Fig. 5a).…”

“…The other energy axis (ω 12 ) is determined by the Fourier transform of the signal with respect to the time delays of the first two phase-locked pulses. Part a adapted with permission from rEF 140 ,. APS.…”

XABOOM: An X-Ray Absorption Benchmark of Organic Molecules Based on Carbon, Nitrogen, and Oxygen 1s → π ∗ Transitions

“…In recent times, the field of X-ray spectroscopy has progressed rapidly as a result of the development and construction of modern synchrotrons and X-ray free-electron lasers (XFELs), enabling the investigation of light-matter interactions at unprecedented time-resolution and radiation intensity. 1,2 These installations facilitate the study of exotic molecular properties and provide a sensitive experimental tool to questions such as (i) probing chemical reactions in real time, as exemplified by the tracking of the photocatalytic cycle in photosynthesis, [2][3][4][5][6] (ii) considering the structure of molecular samples, such as the local structure of liquid water, [7][8][9] (iii) identifying the oxidation state of transition metals in organometallic complexes, with examples including the Fe/Mo atoms in nitrogenase, [10][11][12] (iv) investigating non-linear properties, such as stimulated emission and two-photon absorption, [13][14][15][16][17] and more. By use of pump-probe protocols, time-resolved spectroscopies can study a multitude of dynamical processes, but this potential is yet to be fully explored due to the significant theoretical and experimental difficulties of performing such studies, with, for instance, experimental facilities only being made available during the last decade.…”