Photon-recoil imaging: Expanding the view of nonlinear x-ray physics.

Addressing the ultrafast coherent evolution of electronic wave functions has long been a goal of nonlinear x-ray physics. A first step toward this goal is the investigation of stimulated x-ray Raman scattering (SXRS) using intense pulses from an x-ray free-electron laser. Earlier SXRS experiments relied on signal amplification during pulse propagation through dense resonant media. By contrast, our method reveals the fundamental process in which photons from the primary radiation source directly interact with a single atom. We introduce an experimental protocol in which scattered neutral atoms rather than scattered photons are detected. We present SXRS measurements at the neon K edge and a quantitative theoretical analysis. The method should become a powerful tool in the exploration of nonlinear x-ray physics.

Accurate prediction of X-ray pulse properties from a free-electron laser using machine learning.

Free-electron lasers providing ultra-short high-brightness pulses of X-ray radiation have great potential for a wide impact on science, and are a critical element for unravelling the structural dynamics of matter. To fully harness this potential, we must accurately know the X-ray properties: intensity, spectrum and temporal profile. Owing to the inherent fluctuations in free-electron lasers, this mandates a full characterization of the properties for each and every pulse. While diagnostics of these properties exist, they are often invasive and many cannot operate at a high-repetition rate. Here, we present a technique for circumventing this limitation. Employing a machine learning strategy, we can accurately predict X-ray properties for every shot using only parameters that are easily recorded at high-repetition rate, by training a model on a small set of fully diagnosed pulses. This opens the door to fully realizing the promise of next-generation high-repetition rate X-ray lasers.

Rydberg-resolved resonant inelastic soft x-ray scattering: dynamics at core ionization thresholds.

Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.

High resolution multiphoton spectroscopy by a tunable free-electron-laser light.

Seeded free electron lasers theoretically have the intensity, tunability, and resolution required for multiphoton spectroscopy of atomic and molecular species. Using the seeded free electron laser FERMI and a novel detection scheme, we have revealed the two-photon excitation spectra of dipole-forbidden doubly excited states in helium. The spectral profiles of the lowest (-1,0)(+1) (1)S(e) and (0,1)(0) (1)D(e) resonances display energy shifts in the meV range that depend on the pulse intensity. The results are explained by an effective two-level model based on calculated Rabi frequencies and decay rates.

X-ray emission spectroscopy of hydrogen bonding and electronic structure of liquid water.

We use x-ray emission spectroscopy to examine the influence of the intermolecular interaction on the local electronic structure of liquid water. By comparing x-ray emission spectra of the water molecule and liquid water, we find a strong involvement of the a(1)-symmetry valence-orbital in the hydrogen bonding. The local electronic structure of water molecules, where one hydrogen bond is broken at the hydrogen site, is separately determined. Our results provide an illustration of the important potential of x-ray emission spectroscopy for elucidating basic features of liquids.

Radiative and relativistic effects in the decay of highly excited states in helium

A recent experimental study [J.-E. Rubensson et al., Phys. Rev. Lett. 83, 947 (1999)] measured a significant fluorescence yield of the He( 2lnl(')) photoexcited resonances, showing major qualitative differences from nonrelativistic predictions. We present a further theoretical study of these states, and perform R-matrix multichannel quantum defect theory calculations to extract fluorescence and ionization cross sections. These theoretical results are in excellent agreement with newer, higher-resolution measurements. Radiative and spin-orbit effects are quantified and shown to play an important role in the overall characterization of highly excited states.

Femoral neuropathy: a complication of lithotomy position under spinal anaesthesia. Report of three cases.

Three patients developed solitary unilateral peripheral femoral neuropathy after vaginal hysterectomy. All were operated under subarachnoid analgesia in the lithotomy position. Straight rod leg supports with swing stirrups were used and the procedures lasted for two and one-half hours. The complication is thought due to the extreme abduction of thighs with external rotation at the hip causing ischaemia of the femoral nerve as it is kinked beneath the tough inguinal ligament. The prognosis was found to be excellent with complete recovery within eight to ten weeks. The complication is preventable by using lateral thigh supports limiting the degree of abduction.

Medical termination of pregnancy.

PIP: 300 pregnancies terminated at the Gynecological Out-patient Department of the Government Medical College, Aurangabad, India between April 1972-December 1973, were analyzed to determine the type of clients accepting the method, the reasons for medical termination of pregnancy and the extent to which objectives of the Medical Termination of Pregnancy Act has been fulfilled. The patients were mainly from urban areas (70.6%), 21-20 years of age (67.3%), in the lower income groups (67%), parity 2-3 (45.6%), and over 90% were married. 158 cases were 6-8 weeks of gestation, 67 cases, 10-12 weeks, 34 cases, 14-16 weeks and 41 cases, 18-20 weeks. 207 of the operations were performed to prevent injury to mental health, 79 cases for contraceptive failure, and 14 cases to prevent injury to physical health. In the present series perforation of the uterus occurred in 1.5%, incomplete evacuation in 3.8% and infection in 2%. 77% accepted contraceptive methods.^ieng