3D microoptical elements formed in a photostructurable germanium silicate by direct laser writing

We present our investigations into the fabrication of three-dimensional microoptical elements by the direct femtosecond laser writing of a germanium–silicon photosensitive hybrid material. Germanium glass composites are very interesting for optical applications as they are photosensitive, and maintain high optical transparency in the visible and near-infrared bands of the spectrum. Here, we have used a germanium containing hybrid material to make nanophotonic structures and microoptical elements such as photonic crystal templates, prisms and spatial polarization plates, both on flat surfaces and fiber tips. Our results show that this germanium silicate composite is an excellent material for microoptics fabrication.     

Spatial Filters on Demand Based on Aperiodic Photonic Crystals

Photonic Crystal spatial filters, apart from stand‐alone spatial filtering function, can also suppress multi‐transverse‐mode operation in laser resonators. Here it is shown that such photonic crystals can be designed by solving the inverse problem: for a given spatial filtering profile. Optimized Photonic Crystal filters were fabricated in photosensitive glass. Experiments have shown that such filters provide a more pronounced filtering effect for total and partial transmissivity conditions.     

Picosecond kinetics and transient spectra of pseudoisocyanine monomers and J-aggregates in aqueous solution

Bleaching of monomer and J-aggregate bands of pseudoisocyanine was observed using tunable excitation wavelengths. Both bleached bands decrease with (15 ± 3) ps. A residual J-band bleaching exists up to 1 ns. A new transient absorption in superposition with the J-band was round to consist of two bands with different time behaviour.     

Novel tantalum based photocurable hybrid sol-gel material employed in the fabrication of channel optical waveguides and three-dimensional structures

A novel hybrid organic-inorganic photocurable sol-gel material based on tantalum ethoxide and 3-trimethoxysilylpropylmethacrylate has been developed, characterised and used in the fabrication of optical waveguides and three-dimensional woodpile structures employing the single and two-photon polymerisation techniques, respectively. Single mode waveguides operating at 1310 and 1550 nm have been fabricated, optically characterised and their performances correlated to the material formulation. Three-dimensional woodpile structures exhibiting negligible shrinkage have been developed and their remarkable mechanical stability correlated to the molecular structure of the hybrid material. The overall fabrication process of these devices is described and it is shown that the refractive indices of the materials can be tailored by a precise control of the material composition allowing the successful fabrication of performing single mode waveguides.     

Tuning the refractive index in 3D direct laser writing lithography: towards GRIN microoptics

We report a study of the determination of polymer cross‐linking, namely the degree of conversion and refractive index of the microstructures created by two‐photon polymerization (TPP). The influence of TPP processing parameters such as laser intensity and scanning velocity is investigated. The degree of conversion is analyzed via Raman microspectroscopy and the refractive index is measured with the interferometric technique employing a Michelson interferometer. Moreover, the relationship between these two properties is revealed and details are discussed. The largest refractive index change that we have obtained is of the order of 10⁻². Finally, we propose and demonstrate experimentally the realization of the gradient‐index (GRIN) structure, resulting from a laser‐induced local refractive index modification due to monomer cross‐linking, i.e. degree of conversion. This work implies that the TPP technique is a valuable tool for the fabrication of GRIN microoptics for (in)homogeneous molding of light flow at the micrometer scale.

     

In vitro and in vivo biocompatibility study on laser 3D microstructurable polymers

Films and microstructured scaffolds have been fabricated using direct laser writing out of different polymers: hybrid organic-inorganic ORMOCORE b59, acrylate-based AKRE23, novel organic-inorganic Zr containing hybrid SZ2080, and biodegradable PEG-DA-258. Adult myogenic stem cells were grown on these surfaces in vitro. Their adhesion, growth, and viability test results suggest good potential applicability of the materials in biomedical practice. Pieces of these polymers were implanted in rat’s paravertebral back tissue. Histological examination of the implants and surrounding tissue ex vivo after 3 weeks of implantation was conducted and results show the materials to be at least as biocompatible as surgical clips or sutures. The applied direct laser writing technique seems to offer good future prospects in a polymeric 3D scaffold design for artificial tissue engineering with autologous stem cells.     

Picosecond absorption spectroscopy and its application to the study of nucleic acid components

A high performance picosecond absorption spectrometer adapted for induced absorption measurements in the UV region is described. An application of the spectrometer to the study of nucleic acids (NA) components is presented. Experimental results are given of induced absorption measurements in water solutions of NA components and in single crystals of NA bases.     

PICOSECOND ABSORPTION STUDIES OF Zn-OCTAETHYLPORPHIN π-MONOANIONS

Abstract— Using the example of Zn-octaethylporphin π-monoanion solution in tetrahydrofuran, we studied the dynamics of ultrafast photoprocesses in porphyrin π-anions using a tunable picosecond absorption spectrometer. The deactivation kinetics of the lowest excited electronic (doublet) state of Zn-octaethylporphin iT-monoanion has been determined and was found to be followed by a single exponential function with the characteristic time 135 ps. It is shown that upon picosecond excitation to the long wavelength absorption band (λ_max= 830 nm) the process of two-quantum photoionization of the involved monoanion is easily realized, with the results that the observable kinetics of spectral changes exhibit a strong dependence on the excitation intensity.     

Picosecond time-resolved spectroscopic studies of a monomer—dimer system of 3,3′-diethyl thiacarbocyanne iodide in aqueous solution

Transient absorption in the blue and near-infrared and bleaching of 3,3'-diethyl thiacarbocyanine iodide monomers and dimers weres studied. The monomer excited-state lifetime is 145 ± 10 ps, the recovery time of the dimers is 460 ± 50 ps. An intermediate state with a rise time of 80 ps and decay time of 500 ps has been detected between 670 and 730 nm.