5 research outputs found
Anomalous nonlinear X-ray Compton scattering
X-ray scattering is typically used as a weak linear atomic-scale probe of matter. At high intensities, such as produced at free-electron lasers, nonlinearities can become important, and the probe may no longer be considered weak. Here we report the observation of one of the most fundamental nonlinear X-ray–matter interactions: the concerted nonlinear Compton scattering of two identical hard X-ray photons producing a single higher-energy photon. The X-ray intensity reached 4 × 1020 W cm−2, corresponding to an electric field well above the atomic unit of strength and within almost four orders of magnitude of the quantum-electrodynamic critical field. We measure a signal from solid beryllium that scales quadratically in intensity, consistent with simultaneous non-resonant two-photon scattering from nearly-free electrons. The high-energy photons show an anomalously large redshift that is incompatible with a free-electron approximation for the ground-state electron distribution, suggesting an enhanced nonlinearity for scattering at large momentum transfer
Anomalous nonlinear X-ray Compton scattering
X-ray scattering is typically used as a weak linear atomic-scale probe of matter. At high intensities, such as produced at free-electron lasers, nonlinearities can become important, and the probe may no longer be considered weak. Here we report the observation of one of the most fundamental nonlinear X-ray–matter interactions: the concerted nonlinear Compton scattering of two identical hard X-ray photons producing a single higher-energy photon. The X-ray intensity reached 4 × 1020 W cm−2, corresponding to an electric field well above the atomic unit of strength and within almost four orders of magnitude of the quantum-electrodynamic critical field. We measure a signal from solid beryllium that scales quadratically in intensity, consistent with simultaneous non-resonant two-photon scattering from nearly-free electrons. The high-energy photons show an anomalously large redshift that is incompatible with a free-electron approximation for the ground-state electron distribution, suggesting an enhanced nonlinearity for scattering at large momentum transfer
Negative Pressures and Spallation in Water Drops Subjected to Nanosecond Shock Waves
Most experimental
studies of cavitation in liquid water at negative
pressures reported cavitation at tensions significantly smaller than
those expected for homogeneous nucleation, suggesting that achievable
tensions are limited by heterogeneous cavitation. We generated tension
pulses with nanosecond rise times in water by reflecting cylindrical
shock waves, produced by X-ray laser pulses, at the internal surface
of drops of water. Depending on the X-ray pulse energy, a range of
cavitation phenomena occurred, including the rupture and detachment,
or spallation, of thin liquid layers at the surface of the drop. When
spallation occurred, we evaluated that negative pressures below −100
MPa were reached in the drops. We model the negative pressures from
shock reflection experiments using a nucleation-and-growth model that
explains how rapid decompression could outrun heterogeneous cavitation
in water, and enable the study of stretched water close to homogeneous
cavitation pressures