Two and three dimensional structures with micron and submicron resolution have been achieved in commercial resists,
polymeric materials and sol-gel materials by several lithographic techniques. In this context, silicon-based sol-gel
materials are particularly interesting because of their versatility, chemical and thermal stability, amount of embeddable
active compounds. Compared with other micro- and nano-fabrication schemes, the Two Photon Induced Polymerization
is unique in its 3D processing capability. The photopolymerization is performed with laser beam in the near-IR region,
where samples show less absorption and less scattering, giving rise to a deeper penetration of the light. The use of
ultrashort laser pulses allows the starting of nonlinear processes like multiphoton absorption at relatively low average
power without thermally damaging the samples.
In this work we report results on the photopolymerization process in hybrid organic-inorganic films based
photopolymerizable methacrylate-containing Si-nanobuilding blocks. Films, obtained through sol-gel synthesis, are
doped with a photo-initiator allowing a radical polymerization of methacrylic groups. The photo-initiator is activated by
femtosecond laser source, at different input energies. The development of the unexposed regions is performed with a
suitable solvent and the photopolymerized structures are characterized by microscopy techniques.
We report here the nonlinear absorption of bifluorene derivatives induced by two-photon absorption (TPA), in order to study the effect of the dimension of the molecule on these properties. Measurements were performed in chloroform between 450 and 650 nm for nanosecond time duration pulses. The nonlinear absorption is attributed to a three-photon absorption process involving a first TPA step followed by an excited state absorption process. The 2D first generation organic dendrimer presents the highest values of the corresponding three-photon absorption coefficient α3, while the 3D systems presents lower efficiencies close to that of the bifluorene itself.
We demonstrate the possibility of optically inducing the resolution of a racemic mixture of molecules. We thus measured an optical induction of optical rotation. For this, we used an all optical method based on a pump (Ar-488 nm) - probe (He-Ne-632 nm) experiment exciting a thin layer of a new chiral photoisomerizable chromophore in a PMMA matrix.
We report here the caracterization of efficient photoinitiators for radicalar polymerization by two-photon absorption (TPA). Symmetric molecules bearing tertiary amines as a donor group D and a biphenyl or a fluorene for the transmitting electron group π were proposed for the visible. For IR, the selected phoinitiator presents the general structure D-π-A-π-D, in which A is an acceptor group. The initiation efficiencies of these systems were evaluated by the determination of the threshold intensities for a given exposure duration. Molecules for the visible are more sensitive than those designed for IR. Comparing to the commercial resins for UV photopolymerization generally involved for TPA, these optimized intiators led to a significant increase of the sensitivity during fabrication. Weaker incident intensities and faster scanning speeds could be used. This approach led the fabrication of tridimensional micro-objects with a less onerous nanosecond pulses microlaser.
We measure third-order optical response of two organometallic compounds using the degenerate four wave mixing method. From measurements of DFWM efficiency, we deduce the values of third-order susceptibilities χ<3>. From measurements of χ<3>, we deduce the values of the second-order hyperpolarisabilities γ. The merit factor for each compound is given and the value obtained for the most efficient compound in terms of γ(second order hyperpolarizability) is 104 larger than the value of CS2, which is a reference material. The obtained optical nonlinearities are compared to those of other compounds previously studied. A preliminary correlation between structure and third-order optical properties is proposed.
All-optical poling technique permits purely optical orientation of dye molecules in a polymer film. The experiment includes two phases: the writing (seeding) period and the readout one. In seeding phase two beams, the fundamental (omega) and its second harmonic (SH, 2(omega) ) irradiate the sample and as a result of the coherent interference between them the second order (chi) (2)-susceptibility grating is encoded, with a period satisfying the phase matching condition for SH generation. During the readout step only the fundamental beam is incident onto the material and the second harmonic beam generated by the medium is observed at the back side of the sample. The coherent superposition of two beams at (omega) and 2(omega) frequencies results in a presence of a polar field E(t) inside the material, which can break the centrosymmetry of the medium. The physical origin of the effect lies in the orientational hole-burning in the initially isotropic distribution of dye molecules. It has been demonstrated that efficient all-optical poling requires optimization of relative intensities and relative phase of the seeding beams. An original technique of non-perturbative monitoring of the all-optical poling process without any necessity of taking care of the phase difference between seeding beams is presented. This new technique was applied to several new dye-polymer systems.