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.     

A computational study of the error in the vortex method associated with discontinuous vorticity

We investigate computationally the error computed by the vortex method for a discontinuous patch of vorticity. Specifically, the computed velocity and vorticity of an elliptical path of constant vorticity, known as the Kirchhoff ellipse, are compared to the analytic velocity and vorticity. The error in the velocity and the vorticity for the Kirchhoff ellipse as computed by the vortex method is presented. This error is studied as a function of the aspect ratio of the ellipse, the blob function, the spacing between the centers of the computational elements, and the blob radius. Both the error at the initial time and the error after three revolutions of the ellipse are discussed. © 1996 John Wiley & Sons, Inc.     

CARS measurements of temperature and species concentrations in an IC engine

Temperature measurements alone, and also simultaneous CO₂ concentration and temperature measurements, have been performed inside a fired IC engine. To tackle the two main problems encounted when making measurements in an engine (i.e., cycle-to-cycle variations and beam steering by density gradients), the shot-by-shot referencing technique and the in situ referencing technique using N₂ to determine [CO₂] were used. The temperature is deduced from the broadband N₂ CARS signal and narrow band detection is used for CO₂. A representative example of temperature measurements is given which shows a correlation between temperature and knocking intensity in the burnt gas of a knocking engine. The first simultaneous determinations of temperature and [CO₂] are also reported; so far these are reliable only during the compression stoke.     

Characterization of DNA chips on the molecular scale before and after hybridization with an atomic force microscope

Using two different 25-mer oligonucleotide probes covalently grafted on a silicon substrate, we demonstrate how efficient atomic force microscopy (AFM) can be for monitoring each step of DNA chip preparation: from probe immobilization to hybridization on the molecular scale. We observed the probe-molecule organization on the chip after immobilization, and the target molecules, which hybridized with probes could be individually identified. This article presents a method of straightforwardly identifying not only single and double DNA strands, but also, and more significantly, the hybridized part on them.     

Random Classical Fidelity

We introduce a random perturbed version of the classical fidelity and we show that it converges with the same rate of decay of correlations, but not uniformly in the noise. This makes the classical fidelity unstable in the zero-noise limit.     

Coherent anti-Stokes Raman scattering microscopy with a photonic crystal fiber based light source

A coherent anti-Stokes Raman scattering microscope based on a Ti:sapphire femtosecond oscillator and a photonic crystal fiber is demonstrated. The nonlinear response of the fiber is used to generate the additional wavelength needed in the Raman process. The applicability of the setup is demonstrated by imaging of micrometer-sized polystyrene beads.     

Acetylene on Cu(111): imaging a molecular surface arrangement with a constantly rearranging tip

Acetylene on Cu(111) is investigated by scanning tunnelling microscopy (STM); a surface pattern previously derived from diffraction measurements can be validated, if the variation of the STM image transfer function through absorption of an acetylene molecule onto the tip apex is taken into account. Density functional theory simulations point to a balance between short-range repulsive interactions of acetylene/Cu(111) associated with surface stress and longer range attractive interactions as the origin of the ordering.     

Wide electrical tunability of a GaInAsP/InP microdisk resonator

We report on the characterization of an InP/InGaAsP-material-based microdisk resonator optical filter. The originality here is constituted by the use of a localized control electrode that is used for the tuning of the resonance wavelength of the filter via the injection of a driving current. Tuning of the resonance wavelength close to 8 nm has been experimentally achieved for a drive current of 80 mA.     

Commissioning of a multi‐beamline femtoslicing facility at SOLEIL

The investigation of ultrafast dynamics, taking place on the few to sub‐picosecond time scale, is today a very active research area pursued in a variety of scientific domains. With the recent advent of X‐ray free‐electron lasers (XFELs), providing very intense X‐ray pulses of duration as short as a few femtoseconds, this research field has gained further momentum. As a consequence, the demand for access strongly exceeds the capacity of the very few XFEL facilities existing worldwide. This situation motivates the development of alternative sub‐picosecond pulsed X‐ray sources among which femtoslicing facilities at synchrotron radiation storage rings are standing out due to their tunability over an extended photon energy range and their high stability. Following the success of the femtoslicing installations at ALS, BESSY‐II, SLS and UVSOR, SOLEIL decided to implement a femtoslicing facility. Several challenges were faced, including operation at the highest electron beam energy ever, and achievement of slice separation exclusively with the natural dispersion function of the storage ring. SOLEIL's setup also enables, for the first time, delivering sub‐picosecond pulses simultaneously to several beamlines. This last feature enlarges the experimental capabilities of the facility, which covers the soft and hard X‐ray photon energy range. In this paper, the commissioning of this original femtoslicing facility is reported. Furthermore, it is shown that the slicing‐induced THz signal can be used to derive a quantitative estimate for the degree of energy exchange between the femtosecond infrared laser pulse and the circulating electron bunch.