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

Medical Practice and Review Experience with the use of sugar paste dressing followed by reconstruction of sacral pressure sore with V-Y flap: A reliable solution for a major problem

Pressure sore is a complication in paraplegic/quadriplegic patients. Despite advances in reconstruction techniques, sacral pressure sores are still a challenge to the orthopaedic surgeon, because of long hospital stay resulting into the situation where pressure sores are in evitable for ambulatory patients too. Development of pressure sores makes treatment/rehabilitation difficult and delays treatment options. Additionally, untreated sores cause complications, e.g. death and recurrence after surgery. Attention has been focused on aggressive dressing of the deep sores with use of sugar paste. Once granulation tissue had filled a sore cavity, a surgical closure using V-Y flaps were considered a method providing better treatment results. This study was conducted on 14 patients (10 males and 4 females) with sacral pressure sores in age group of 35 to 80 years. After initial debridement and removal of tissues of doubtful viability, culture and sensitivity were done in all cases. Wounds were packed with sugar paste for 5 to 14 days or till cavity is filled by granulation tissue. Bilateral V-Y myocutaneous flaps were used in 13 cases. Wound gaping occurred in 1 due to failure of a unilateral rotational flap and secondary bilateral V-Y myocutaneous flaps were needed. Suction drains retained for 7 to 10 days and pressure bearing on sores sites was avoided till complete healing. Superficial infection occurred in 3 cases which responded to suction and dressings. In our experience, the use of sugar paste dressing as a preprocedure to V-Y flap covering operation is a reliable options in management of infected deep sacral pressure sore

Solid-state harmonics beyond the atomic limit

Strong-field laser excitation of solids can produce extremely nonlinear electronic and optical behaviour. As recently demonstrated, this includes the generation of high harmonics extending into the vacuum-ultraviolet and extreme-ultraviolet regions of the electromagnetic spectrum. High harmonic generation is shown to occur fundamentally differently in solids and in dilute atomic gases. How the microscopic mechanisms in the solid and the gas differ remains a topic of intense debate. Here we report a direct comparison of high harmonic generation in the solid and gas phases of argon and krypton. Owing to the weak van der Waals interaction, rare (noble)-gas solids are a near-ideal medium in which to study the role of high density and periodicity in the generation process. We find that the high harmonic generation spectra from the rare-gas solids exhibit multiple plateaus extending well beyond the atomic limit of the corresponding gas-phase harmonics measured under similar conditions. The appearance of multiple plateaus indicates strong interband couplings involving multiple single-particle bands. We also compare the dependence of the solid and gas harmonic yield on laser ellipticity and find that they are similar, suggesting the importance of electron-hole recollision in these solids. This implies that gas-phase methods such as polarization gating for attosecond pulse generation and orbital tomography could be realized in solids