Functionalization of micro-size garnet at the end of optical fiber for magneto-optical applications.

We utilized a metal propionate solution to prepare polycrystalline bismuth-substituted yttrium iron garnets through the metal-organic decomposition process. After conducting thorough optimization, we successfully synthesized a garnet that exhibited a high magneto-optic response directly at the end of an optical fiber. A notable achievement of our work lies in the ability to restrict the size and position of the garnet to match the dimensions of the fiber's core. The functionalized fiber was integrated into a magneto-optical sensor setup, offering the flexibility to operate either in the Faraday rotation or magnetic circular dichroism mode.

Control of the Organization of 4,4'-bis(carbazole)-1,1'-biphenyl (CBP) Molecular Materials through Siloxane Functionalization.

We show that through the introduction of short dimethylsiloxane chains, it was possible to suppress the crystalline state of CBP in favor of various types of organization, transitioning from a soft crystal to a fluid liquid crystal mesophase, then to a liquid state. Characterized by X-ray scattering, all organizations reveal a similar layered configuration in which layers of edge-on lying CBP cores alternate with siloxane. The difference between all CBP organizations essentially lay on the regularity of the molecular packing that modulates the interactions of neighboring conjugated cores. As a result, the materials show quite different thin film absorption and emission properties, which could be correlated to the features of the chemical architectures and the molecular organizations.

Effect of the electron donating group on the excited-state electronic nature and epsilon-near-zero properties of curcuminoid-borondifluoride dyes.

Epsilon-near-zero (ENZ) properties have been reported in organic molecular films. In particular, cyanine and squaraine films have been shown to exhibit ENZ properties in the visible spectral region with a strong 3rd order nonlinear optical response near the ENZ spectral region. Noting both cyanine and squaraine belong to the polymethine family, a series of six curcuminoid borondifluoride (Curc) derivatives were developed to examine whether such a polymethine character is positively correlated with the ENZ property of the organic films. Those Curc derivatives possess a Donor-Acceptor-Donor (D-A-D) architecture with acceptor, AcacBF2, located at the molecular center. The backbone of Curc is designed such that the donor strength can be tuned to transit between charge transfer (CT) and polymethine character. This balance between CT and polymethine character of the Curc series is examined based on the Lippert-Mataga plot. As donor strength in the D-A-D structure increases, CT character is less marked resulting in a more dominant polymethine character. The structural and optical properties of the Curc films with a thickness in the order of 30 nm were examined to correlate the polymethine character with the ENZ response. The results obtained in isotropic Curc thin films demonstrate that an increase of polymethine character associated with a stronger donor strength leads to an appearance/enhancement of the ENZ property in the visible spectrum range from 500 to 670 nm. Overall, this study provides useful guidelines to engineer new organic materials showing ENZ properties in a desired spectral range.

Functionalization of Biphenylcarbazole (CBP) with Siloxane-Hybrid Chains for Solvent-Free Liquid Materials.

We report herein the synthesis of siloxane-functionalized CBP molecules (4,4'-bis(carbazole)-1,1'-biphenyl) for liquid optoelectronic applications. The room-temperature liquid state is obtained through a convenient functionalization of the molecules with heptamethyltrisiloxane chains via hydrosilylation of alkenyl spacers. The synthesis comprises screening of metal-catalyzed methodologies to introduce alkenyl linkers into carbazoles (Stille and Suzuki Miyaura cross-couplings), incorporate the alkenylcarbazoles to dihalobiphenyls (Ullmann coupling), and finally introduce the siloxane chains. The used conditions allowed the synthesis of the target compounds, despite the high reactivity of the alkenyl moieties bound to π-conjugated systems toward undesired side reactions such as polymerization, isomerization, and hydrogenation. The features of these solvent-free liquid CBP derivatives make them potentially interesting for fluidic optoelectronic applications.

High-Efficiency Second-Harmonic Generation from Hybrid Light-Matter States.

We report a novel approach to modify the second order nonlinear optical (NLO) susceptibility of organic nanofiber crystals by hybridization with the optical modes of microcavities in the strong coupling regime. The wavelength dependence of the SHG efficiency displays two intense peaks corresponding to the so-formed light-matter hybrid states. Our results demonstrate an enhancement of the resonant SHG efficiency of the lower polariton by 2 orders of magnitude for the collectively coupled molecules as compared to that of the same material outside the microcavity. This study is a proof of principle that opens a new direction for NLO of organic materials in subwavelength resonators.

Low threshold amplified spontaneous emission and ambipolar charge transport in non-volatile liquid fluorene derivatives.

Highly fluorescent non-volatile fluidic fluorene derivatives functionalized with siloxane chains were synthesized and used in monolithic solvent-free liquid organic semiconductor distributed feedback lasers. The photoluminescence quantum yield values, the amplified spontaneous emission thresholds and the ambipolar charge carrier mobilities demonstrate that this class of materials is extremely promising for organic fluidic light-emitting and lasing devices.

Light induced self-written waveguides interactions in photopolymer media.

We present experimental and theoretical study of the interaction of Light Induced Self-Written (LISW) waveguides in photopolymers. We show that the diffusion of the monomer controls the refractive index distribution. Consequently it influences the interaction between the LISW channels allowing the observation of anti-crossing behavior or the propagation of an array of non interacting LISW waveguides.

Synthesis, photophysics and nonlinear optical properties of stilbenoid pyrimidine-based dyes bearing methylenepyran donor groups.

The nonlinear properties and the photophysical behavior of two π-conjugated chromophores that incorporate an electron-deficient pyrimidine core (A) and γ-methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes' scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end-groups. This latter structural parameter also has a strong influence on the excited-state dynamics, which leads to a very efficient fluorescence quenching.

Solvent-free fluidic organic dye lasers.

We report on the demonstration of liquid organic dye lasers based on 9-(2-ethylhexyl)carbazole (EHCz), so-called liquid carbazole, doped with green- and red-emitting laser dyes. Both waveguide and Fabry-Perot type microcavity fluidic organic dye lasers were prepared by capillary action under solvent-free conditions. Cascade Förster-type energy transfer processes from liquid carbazole to laser dyes were employed to achieve color-variable amplified spontaneous emission and lasing. Overall, this study provides the first step towards the development of solvent-free fluidic organic semiconducting lasers and demonstrates a new kind of optoelectronic applications for liquid organic semiconductors.

Electro-optic phase modulation in light induced self-written waveguides propagated in a 5CB doped photopolymer.

We present the inscription of a Light Induced Self-Written (LISW) waveguide in a 4-cyano-4'-pentylbipheny (5CB) doped photopolymer. The dynamic reorientation of the 5CB molecules in the material under applied electric field leads to birefringence in LISW waveguide and thus allows the control of the phase of the guided mode.

Polarization state studies in second harmonic generation signals to trace atherosclerosis lesions.

We have performed multi-photon image reconstructions as well as polarization state analyses inside an artery wall affected by atherosclerosis to investigate the changes in collagen structure. Mice, either healthy or affected by spontaneous atherosclerosis, have been used for this purpose. A two-photon imaging system has been used to investigate atherosclerotic lesions in the ascending aorta of mice. Second harmonic imaging has been performed alternatively on healthy samples and on affected region. The reconstructed images show that the spatial distribution of the collagen network seems disorganized by the disease. The polarization state studies reveal however that the apparent disorganization of the collagen is related to its spatially diffuse distribution and that the internal structure of the collagen fibers is not affected by the disease. In addition, a theoretical simulation of the second harmonic polarization states shows that they are consistent with the known 3D structure of the collagen network.

Filamentation-free self-written waveguides in a photopolymerizable medium initiated by multimode optical fibers.

The inscription of light-induced self-written waveguides (LISW) with multimode optical fibers cannot be achieved by using coherent light because of the filamentation phenomena coming from the interferences among the different propagating modes. To suppress this filamentation, we have used two distinct strategies, an incoherent light writing technique and an "on the flow" writing process, to demonstrate the buildup of 1.5 mm long multimode LISWs.

Multi-level diffractive optical elements produced by excimer laser ablation of sol-gel.

Material ablation by excimer laser micromachining is a promising approach for structuring sol-gel materials as we demonstrate in the present study. Using the well-known direct etching technique, the behaviour of different hybrid organic/inorganic self-made sol-gel materials is examined with a KrF* laser. Ablated depths ranging from 0.1 to 1.5 microm are obtained with a few laser pulses at low fluence (< 1 J/cm(2)). The aim is to rapidly transfer surface relief multi-level diffractive patterns in such a substrate, without intermediate steps. The combination with the 3D profilometry technique of coherence probe microscopy permits to analyse the etching process with the aim of producing multi-level Diffractive Optical Elements (DOE). Examples of four-level DOEs with 10 microm square elementary cells are presented, as well as their laser reconstructions in the infrared.

Rewritable optical data storage in azobenzene copolymers.

We propose to encode optical information through the localized depoling of polar chromophores in thin films of grafted polymeric materials with a femtosecond near IR laser source. This disorientation is promoted through the photoisomerization of the azo-dye component induced by a twophoton absorption process. We show that the resulting localized loss in second harmonic generation efficiency can be exploited in data storage applications. The low irradiation powers used allow for a recycling by reheating and repoling the films leading to a rewritable system.

Quasi-solitonic behavior of self-written waveguides created by photopolymerization.

We investigated the condition of unique self-written channel and multichannel propagation inside bulk photopolymerizable materials. Light was introduced in the medium by a single-mode optical fiber. At a very low beam power of 5 muW , a unique uniform-channel waveguide without any broadening was obtained by polymerization. When the input power is increased to 100 muW , the guide becomes chaotic and multichannel. We connected two fibers separated by a 1-cm distance. The results open the door to studies of the optical and electro-optical properties of photopolymerized guides doped by nonlinear optical chromophores and to possible applications in integrated optical devices.