Denis Gindre

Reversible Two-Photon Optical Data Storage in Coumarin-Based Copolymers

A functionalized polymer film allowing for a complete and straightforward second-harmonic generation (SHG)-assisted high-contrast writing-reading-erasing-writing sequence is proposed. The whole process is supported by the reversible photoinduced dimerization of a coumarin chromophore and enables efficient optical data storage that can be detected only by SHG imaging.

Crystalline Arrays of Pairs of Molecular Rotors: Correlated Motion, Rotational Barriers, and Space-Inversion Symmetry Breaking Due to Conformational Mutations

The rod-like molecule bis((4-(4-pyridyl)ethynyl)bicyclo[2.2.2]oct-1-yl)buta-1,3-diyne, 1, contains two 1,4-bis(ethynyl)bicyclo[2.2.2]octane (BCO) chiral rotators linked by a diyne fragment and self-assembles in a one-dimensional, monoclinic C2/c centrosymmetric structure where two equilibrium positions with large occupancy imbalance (88% versus 12%) are identified on a single rotor site. Combining variable-temperature (70-300 K) proton spin-lattice relaxation, (1)H T1(-1), at two different (1)H Larmor frequencies (55 and 210 MHz) and DFT calculations of rotational barriers, we were able to assign two types of Brownian rotators with different activation energies, 1.85 and 6.1 kcal mol(-1), to the two (1)H spin-lattice relaxation processes on the single rotor site. On the basis of DFT calculations, the low-energy process has been assigned to adjacent rotors in a well-correlated synchronous motion, whereas the high-energy process is the manifestation of an abrupt change in their kinematics once two blades of adjacent rotors are seen to rub together. Although crystals of 1 should be second harmonic inactive, a large second-order optical response is recorded when the electric field oscillates in a direction parallel to the unique rotor axle director. We conclude that conformational mutations by torsional interconversion of the three blades of the BCO units break space-inversion symmetry in sequences of mutamers in dynamic equilibrium in the crystal in domains at a mesoscopic scale comparable with the wavelength of light used. A control experiment was performed with a crystalline film of a similar tetrayne molecule, 1,4-bis(3-((trimethylsilyl)ethynyl)bicyclo[1.1.1]pent-1-yl)buta-1,3-diyne, whose bicyclopentane units can rotate but are achiral and produce no second-order optical response.

Polymer thin-film distributed feedback tunable lasers

We report on measurements of laser emission from poly-methylmethacrylate and poly-vinyl carbazole polymer films doped with rhodamine-6G, DCM and coumarin laser dyes in an optically pumped distributed feedback scheme. We obtain tunability on a broad spectral range for all samples. We show the impact of waveguiding in the polymer film on reducing the laser threshold. We also show that the number of laser modes increases with the polymer film thickness, following the guided mode dispersion.

A Mechanofluorochromic Push–Pull Small Molecule with Aggregation‐Controlled Linear and Nonlinear Optical Properties

A small push-pull molecule involving a diphenylamine substituted by an oligo-oxyethylene chain is described. The compound exhibits aggregation-induced emission with solvent-dependent emission wavelength. Spin-cast deep-red amorphous films rapidly self-reorganize into colorless crystalline films which exhibit mechanofluorochromism and aggregation-induced second-harmonic generation.

Physical origin of the third order nonlinear optical response of orthogonal pyrrolo-tetrathiafulvalene derivatives

We present the third order nonlinear optical study of tetrathiafulvalene-based molecular corners. Degenerate four-wave mixing measurements have been done to provide information about the magnitude and the origin of the nonlinearity, while the nonlinear absorption has been separately measured by performing “open aperture” Z-scan measurements. The response has been found to be strongly dependent upon the structure of the molecular corners.

Opportunities of deoxyribonucleic acid complexes composites for nonlinear optical applications

In this paper, we illustrate new functionalities for nonlinear optical applications of bio-molecular systems. This study presents DNA complex with new ionic surfactants. These surfactants enabled DNA solubility in solvents other than alcohols, like aromatic and chlorinated ones. Composites with two nonlinear optical (NLO) active dyes are subjects of the second and third harmonic generation experiments. The found effective nonlinear susceptibilities values are much higher than that for standard fused silica. We also demonstrate any influence of the surfactant on NLO properties.

Effect of the counter cation on the third order nonlinearity in anionic Au dithiolene complexes

In this work, we present the third order nonlinear optical investigation of two gold complexes, which differ by the nature of the counter cations. The impact of the different design in the architecture through a set of hydrogen bonds in the case of Au-Mel of the systems on the nonlinearity has been studied by means of the Z-scan setup under 532 nm, 30 ps laser excitation, allowing for the determination of the nonlinear absorption and refraction of the samples. Significant modification of the nonlinear optical response between the two metal complexes has been found suggesting a clear effect of the counter cation.

Constructive action of the speckle noise in a coherent imaging system

A coherent imaging system with speckle noise is devised and analyzed. This demonstrates the possibility of improving the nonlinear transmission of a coherent image by increasing the level of the multiplicative speckle noise. This noise-assisted image transmission is a novel instance of stochastic resonance phenomena by which nonlinear signal processing benefits from a constructive action of noise.

Toward submicrometer optical storage through controlled molecular disorder in azo-dye copolymer films

While information encoding through optically induced orientation of azo dyes in organic matrices is being extensively pursued, we propose the alternative of starting out with poled films and to locally reduce their second-harmonic generation capacity by a focused near-infrared femtosecond laser beam of moderate intensity. Arrays of dots irradiated under varying conditions are subsequently imaged in situ as dark spots on a bright background. The samples are also examined through conventional optical microscopy and through atomic force microscopy. We demonstrate that, of these techniques, second-harmonic imaging performs best in the task of information retrieval.

Tunable circularly polarized lasing emission in reflection distributed feedback dye lasers.

A tunable circularly polarized distributed feedback (DFB) laser based on reflection grating configuration was realized in a solution of 4- (dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) doped methanol. Chiral photonic DFB structures with tunable photonic bandgap were generated by controlling the state of polarization of the two interfering pump beams. The dual-peak lasing emission spectrum indicates that the periodic chiral DFB grating is affected by a combination of modulations of gain and refractive index.