Effects of self, induced and cross phase modulations on the generation of picosecond and femtosecond white light supercontinua

The effects of self, induced, and cross phase modulations on the generation of picosecond and femtosecond « white » laser pulses are reviewed. Recent measurements of cross and induced phase modulations are reported using femtosecond and picosecond laser pulses.Les processus de génération d'impulsions lasers femtosecondes et picosecondes à très large bande spectrale sont passés en revue. Les effets des modulations de phase : automodulation (SPM), modulation induite (IPM), et modulation croisée (XPM) sont discutés. De nouvelles mesures des modulations de phase induites et croisées sont reportées

Enhanced two-photon absorption with dimers of π-conjugated molecules

International audienceThe two-photon absorption (TPA) of three organic monomers and dimers with different conjugated systems (biphenyl, fluorene and stilbene) is investigated. Quantum chemistry calculations show an order of magnitude enhancement of the dimer TPA in comparison to the monomer TPA, and an increase of TPA with the strength of the conjugated system. The measured TPA spectra of dimers are in good agreement with calculations. At resonance, the TPA cross-sections of biphenyl, fluorene and stilbene dimers are 1.5, 6 and 13×10−49 cm4 s/photon-molecule, respectively

SPECTROSCOPY AND NONLINEAR PROPRETIES OF CHARGE TRANSFER ORGANIC CRYSTALS

Conventional spectroscopy is used to characterize the parameters of the intense electronic transition of internal charge transfer character of a series of D-A paradisubstituted benzenes in the monocrystal. The implications of new transitions and the influence of intermolecular interactions on non-linear properties are discussed

Efficient initiators for two-photon induced polymerization in the visible range

International audienceWe present two derivatives of biphenyl or fluorene symmetrically substituted, which could initiate the two-photon absorption (TPA) photopolymerization of acrylates in the visible range. Both compounds show broadband TPA between 500 and 650 nm with cross-sections of, respectively, 30 and 80×10−50 cm4 s photon−1 at 532 nm, the photoinitiation wavelength. Threshold energies and dynamic ranges for polymerization were measured in both cases. As expected, the fluorene derivative was slightly more efficient than the biphenyl one. Our initiators appeared to be orders of magnitude more sensitive than the commercial UV ones, commonly used for TPA photopolymerization

Confined nucleation and growth of organic nanocrystals in sol-gel matrices for biophotonics

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New initiator for two-photon absorption induced polymerization with a microlaser at 1.06 μm

International audienceTwo-photon absorption (TPA) induced polymerization is a very promising way for three-dimensional (3D) microfabrication. However, the necessity to use onerous femtosecond Ti:sapphire lasers appears as a major drawback for this technology. We present a new symmetrical conjugated ketone with terminal amino groups that can initiate TPA photopolymerization of acrylates when irradiated with an inexpensive Nd-YAG microlaser. This compound shows broad band TPA between 800 nm and 1100 nm with a cross-section of 100×10−50 cm4 s photon−1 at the photoinitiation wavelength (1.06 μm). The efficiency of this new initiator is evaluated by the determination of the threshold of absorbed energy density for polymerization

Novel 5-(oligofluorenyl)-1,10-phenanthroline type ligands: synthesis, linear and two-photon absorption properties

International audienceThe synthesis and characterization of new 1,10-phenanthroline-based chromophores LT1, LT2 and LD1 featuring fluorene unit(s) are reported. Their absorption and emission as well as their two-photon absorption properties in the 450–650 nm spectral range are discussed in comparison with the parent 1,10-phenanthroline and already described ligands L1 and L2

Optical power limiting properties of organic crystals and nanocrystals in an f/5 optical system

International audienceWe have evaluated the optical limiting properties of transparent organic crystals and nanocrystals in an f/5 optical system. We have studied three organic or organic–inorganic crystals and a sol–gel glass which contains organic nanocrystals of stilbene3. The spectral dependence of the optical limiting curves have shown that broadband limitation can be achieved in the visible range with the 2-amino-5-nitropyridinium-dihydrogenphosphate (2A5NPDP) crystal as the transmitted energy is less than 10 μJ over a wide spectral range (450–600 nm). Results on nanocrystals have indicated that these new materials are a suitable alternative to crystals due to their isotropic response with polarization