V. De Waele

Absolute calibration for a broad range single shot electron spectrometer

This article gives a detailed description of a single shot electron spectrometer which was used to characterize electron beams produced by laser-plasma interaction. Contrary to conventional electron sources, electron beams from laser-plasma accelerators can produce a broad range of energies. Therefore, diagnosing these electron spectra requires specific attention and experimental development. Here, we provide an absolute calibration of the Lanex Kodak Fine screen on a laser-triggered radio frequency picosecond electron accelerator. The efficiency of scintillating screens irradiated by electron beams has never been investigated so far. This absolute calibration is then compared to charge measurements from an integrating current transformer for quasimonoenergetic electron spectra from laser-plasma interaction.

Radiolytic Yield of UIV Oxidation into UVI: A New Mechanism for UV Reactivity in Acidic Solution

The yields of the radiolytic oxidation of U(IV) and of the U(VI) formation, measured by spectrophotometry, are found to be the same (G(-U(IV))(N2O) = G(U(VI))(N2O) = 8.4 x 10(-7) mol J(-1)) and almost double the H(2) formation yield (G(H(2)) = 4.4 x 10(-7) mol J(-1)) in the (60)Co gamma radiolysis of N(2)O-aqueous solutions in the presence of 2 mol L(-1) Cl(-) at pH = 0 (HCl). According to the mechanism of U(IV) radiolytic oxidation, we show that under the conditions of our experiments the U(V) ions do not disproportionate, but undergo a stoichiometric oxidation into U(VI) by H(+) with forming H(2).

Aqueous Solution of UCl62-in O2 Saturated Acidic Medium : An Efficient System To Scavenge All Primary Radicals in Spurs Produced by Irradiation

Absorbance measurements find the yield of the oxidation of U(IV) to be (8.75 +/- 0.05) x 10(-7) mol J(-1) in the (60)Co gamma radiolysis of aqueous solutions containing 4.4 x 10(-3) mol L(-1) U(IV) in the presence of O(2) saturated 2 mol L(-1) Cl(-) at pH = 0. This high value of oxidation yield suggests that all primary radicals formed by water decomposition are scavenged in these solutions. Simulations using a nonhomogeneous stochastic kinetic track model agree with the experimental results and are used to explain the mechanism for scavenging radicals and oxidation of U(IV).

A new single shot terahertz time domain spectrometer for rapid product and process control

A new simple time-domain THz spectrometer based on a single-shot balanced detection of the electric field is presented. It allows for the recording of the full temporal THz profile at kHz acquisition rates. Its performances are demonstrated by measuring the fast drying process of acetone on Teflon.

Does the proton move during ultrafast excited state intramolecular proton transfer

The coherent wavepacket dynamics observed in 35 fs crosscorrelation pumpprobe spectra of 2-(2’-hydroxyphenyl)benzothiazole render a novel and detailed picture of the excited state intramolecular proton transfer, the contributing skeletal deformations and the electronic configuration changes.

From ultrafast spectroscopy to bidirectional molecular switches: DHA/VHF

The photoconversion from dihydroazulene (DHA) to vinylheptafulvene (VHF) is governed by two mechanisms: The ring opening proceeds on the excited energy surface on the picosecond time scale. It is followed by an intemal conversion to the VHF ground state that is accelerated by the presence of a conical intersection in the case of cyclopenta-DHA. This conical intersection hinders the photoinduced back reaction from the final VHF products. However, we successfully photoconverted the cyanophenyl-VHF-cis back to the DHA with a second delayed pulse. This opens the route to the development of bistable DHAs.

Dihydroazulene Molecular Switches: Via Ultrafast Spectroscopy To The First Bidirectional Switch

We demonstrate by using ultrafast time resolved spectroscopy that the photoconversion from dihydroazulene (DHA) to vinylheptafulvene (VHF) is governed by two mechanisms: The ring opening proceeds on the excited energy surface on the picosecond time scale. It is followed by an internal conversion to the VHF ground state that is accelerated by the presence of a conical intersection in the case of cyclopenta-DHA. This conical intersection hinders the photoinduced back reaction from the final VHF products. However, we successfully photo-converted the cyanophenyl-VHF-cis back to the DHA in an experiment with two delayed pulses. This opens the route to the development of bistable dihydroazulene switches.