Pump−probe experiments at the TEMPO beamline using the low‐α operation mode of Synchrotron SOLEIL

The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump–probe experiments. Among others, the low‐α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low‐α mode of the experimental set‐ups developed at the TEMPO beamline to perform pump–probe experiments with soft X‐rays based on photoelectron or photon detection are presented. A 282 kHz repetition‐rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two‐dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time‐resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high‐time‐resolution pump–probe experiments compared and discussed.     

Advances in surface plasmon resonance-based high throughput biochips

This article reviews our recent advances in surface plasmon resonance (SPR) based biochips. It includes four issues, which are the preparation and characterization of high quality gold film, the preparation and characterization of self-assembled monolayer (SAM), dynamics of DNA adsorption on SAMs, and SPRbased microscopies. Numerous topics related to SPR, such as, the modeling of SPR by transmission matrix, effective medium theory, applications of SPR in biology, and SPR-based novel microscopies, are discussed. A novel electrochemical technique, which is extremely useful for the preparation and characterization of high quality SAMs, is also discussed.     

Experimental implementation of a concatenated quantum error-correcting code

Concatenated coding provides a general strategy to achieve the desired level of noise protection in quantum information processing. We report the implementation of a concatenated quantum error-correcting code able to correct phase errors with a strong correlated component. The experiment was performed using liquid-state nuclear magnetic resonance techniques on a four spin subsystem of labeled crotonic acid. Our results show that concatenation between active and passive quantum error correction is a practical tool to handle realistic noise involving both independent and correlated errors.     

Infrared camera based on a curved retina

Design of miniature and light cameras requires an optical design breakthrough to achieve good optical performance. Solutions inspired by animals' eyes are the most promising. The curvature of the retina offers several advantages, such as uniform intensity and no field curvature, but this feature is not used. The work presented here is a solution to spherically bend monolithic IR detectors. Compared to state-of-the-art methods, a higher fill factor is obtained and the device fabrication process is not modified. We made an IR eye camera with a single lens and a curved IR bolometer. Images captured are well resolved and have good contrast, and the modulation transfer function shows better quality when comparing with planar systems.     

Full potential x-ray absorption calculations using time dependent density functional theory

We report the implementation of a fully relativistic time dependent density functional theory (TDDFT) method for carrying out x-ray absorption spectroscopy calculations for extended systems. This is the first time that a TDDFT simulation of x-ray absorption in extended systems has featured a full potential ground state calculation. We prove that this unusual feature of the TDDFT implementation unequivocally yields improvement over the previous muffin-tin calculation methods.     

Relevance of continuously self-imaging gratings for noise robust imagery

We have designed miniaturized, simple, and robust cameras composed of a single diffractive optical element (DOE) that generates a continuously self-imaging (CSI) beam. Two different DOEs are explored: the J₀ Bessel transmittance, characterized by a continuous optical transfer function (OTF) and the CSI grating (CSIG), characterized by a sparse OTF. In this Letter, we will analyze the properties of both DOEs in terms of radiometric performances. We will demonstrate that the noise robustness is enhanced for a CSIG, thanks to the sparsity of its OTF. A camera using this DOE has been made and experimental images are presented to illustrate the noise robustness.     

Nonlinear oscillations beyond caustics

This paper studies the focusing of high-frequency solutions of semilinear hyperbolic equations. In previous papers, we studied two opposite phenomena. First, the focusing of nonlinear waves can force the solutions to blow up, even before reaching the caustics. Second, for strongly dissipative equations, nonlinear oscillations can be completely absorbed when they reach the caustic set. In this paper, we study the intermediate case of equations with globally Lipschitz nonlinearities. The nonlinear oscillations persist after crossing the caustic set. The solutions are described using oscillatory integrals, which are associated with Lagrangian manifolds in the cotangent bundle. The equations of nonlinear geometric optics lift to these manifolds. In contrast to the linear case, the transport equations for amplitudes living above the same points of spacetime are coupled. © 1996 John Wiley & Sons, Inc.     

Ultrafast and nanosecond laser-induced desorption of positive ions from lithium fluoride single crystals

We compare desorption of positive ions from lithium fluoride single crystals following pulsed laser excitation using either femtosecond (180 fs, 265 nm) or nanosecond (3 ns, 266 nm) sources. Following optical excitation, desorbed ions are mass analyzed using standard time-of-flight techniques. Several important differences between nanosecond and femtosecond excitation are revealed. Femtosecond excitation produces higher kinetic energy Li⁺ than does nanosecond excitation (10 eV vs. 5 eV) while nanosecond excitation yields significant quantities of impurity ions Na⁺ and K⁺, in addition to efficient Li⁺ emission. The Li⁺ desorption threshold is similar for both laser sources. This similarity is a surprising result, as sub-bandgap nanosecond pulses are only likely to excite defect states efficiently (via linear excitation), while the ultrahigh peak-power femtosecond pulses could in principle induce multiphoton and avalanche excitation. Femtosecond excitation results in much less complicated time-of-flight spectra, as predominantly Li⁺ is detected with some H⁺ also observed. We have measured the Li⁺ yield as a function of time delay between two sub-threshold femtosecond laser pulses. We find that the majority of the Li⁺ yield decays rapidly, largely within the fs pulse duration. However, a weak but measurable decay component of approximately 2 ps is indicated.