High-efficiency, simple setup for pulse cleaning at the millijoule level by nonlinear induced birefringence

Nonlinear elliptical polarization rotation is used to improve the contrast of femtosecond pulses by several orders of magnitude. Using nonlinear induced birefringence in air, we produced cleaned pulses with an energy of a few hundreds of microjoules. This technique presents several major advantages, such as convenience and stability of the setup. We investigated the phase profile required for obtaining high-energy pulses. No phase distortion is observed, and the spatial quality of the beam is preserved.     

Stochastic resonance to control diffusive motion in chemistry

This paper reports on a novel procedure to tune the effective diffusion coefficient of a field-sensitive reactant in the presence of a periodic external field. We investigate the motion of two negatively charged azo dyes interacting with alpha-cyclodextrin (alpha-CD) upon action of a periodic square wave electrical field. We show that the dyes exhibit an effective diffusion coefficient D(eff) that depends on the rate constants for dye complexation within alpha-CD, the period and the amplitude of the field. UV-vis absorption, gradient field (1)H NMR, and fluorescence correlation spectroscopy (FCS) after two photon excitation are used to evidence that D(eff) may be increased far beyond its intrinsic value when specific relations interpreted as a stochastic resonance are fulfilled. The present results may find useful applications in chemical kinetics as well as for molecular sorting.     

RMN en phase nematique a 400 MHz: etude du vinylidenecyclopropane

The NMR spectrum (400 MHz) of vinylidenecyclopropane oriented in a nematic phase has been analyzed. Information about the geometry has been deduced from the ratios of H-H distances.     

Photoelectron spectra of halogeno-3-propynes (XCH2CCH) and halogenomethylcyanides (XCH2CN) and comments on the attribution of f

The photoelectron spectra of halogeno-3-propynes and halogenomethylcyanides (F, Cl, Br) have been determined. The ionization potentials (IP) of various     

Nonlinear optical transformation of the polarization state of circularly polarized light with holographic-cut cubic crystals

Nonlinear modification of circularly polarized light propagating in holographic-cut cubic crystals is theoretically predicted and experimentally observed. To the best of our knowledge this is the first demonstration of nonlinear modification of circularly polarized light with cubic crystals.     

Photoswitching Kinetics and Phase‐Sensitive Detection Add Discriminative Dimensions for Selective Fluorescence Imaging

Non‐invasive separation‐free protocols are attractive for analyzing complex mixtures. To increase selectivity, an analysis under kinetic control, through exploitation of the photochemical reactivity of labeling contrast agents, is described. The simple protocol is applied in optical fluorescence microscopy, where autofluorescence, light scattering, as well as spectral crowding presents limitations. Introduced herein is OPIOM (out‐of‐phase imaging after optical modulation), which exploits the rich kinetic signature of a photoswitching fluorescent probe to increase selectively and quantitatively its contrast. Filtering the specific contribution of the probe only requires phase‐sensitive detection upon matching the photoswitching dynamics of the probe and the intensity and frequency of a modulated monochromatic light excitation. After in vitro validation, we applied OPIOM for selective imaging in mammalian cells and zebrafish, thus opening attractive perspectives for multiplexed observations in biological samples.     

Photoinduced pH drops in water

A 2-hydroxyazobenzene platform has been evaluated to photorelease protons in aqueous solutions. Three different systems relying on molecular, supramolecular and polymeric strategies have been investigated in order to tune the water solubility and the thermodynamic and kinetic properties. This paper first reports on the syntheses and the physico chemical analyses for each system. Subsequently, we show that the three strategies are appropriate to reversibly photo-generate tunable pH drops in water up to one pH unit amplitude and at the 10-100 s timescale, upon transient illumination at 365 nm.