Massimo Guglielmi

Sensitizing effects in Ag-Er codoped glasses for optical amplification

A set of samples co-doped with Er and Ag were prepared with a combined sol-gel and ion-exchange route. This multistep process sytnthesizes samples in which the silver atoms are dispersed in the matrix and/or aggregated in Ag multimers or nanoclusters. The samples exhibit a different photo-luminescence response depending on the sensitizing effect due to silver atoms. The spectroscopic properties were correlated with the structural properties investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction. The Er3+ excitation via energy transfer, obtained in a wide range of wavelengths, has been clearly related to the presence in the sample of Ag multimers.

Characterization of laser-written sol-gel strip waveguides

The realization of low-loss optical waveguides by the sol-gel method and the subsequent production of strip waveguides by direct laser densification are described. These waveguides have been characterized by both the optical and structural point of view, and the results are discussed.

γ(glicydoxypropyl)-trymethoxysilane-based matrices tailored for optical limiting applications

A hybrid organic-inorganic material derived 3- (glycidoxypropyl)-trimethoxysilane (GPTMS) and fullerene derivatives has been developed for optical limiting applications. The control of the final material has been achieved by engineering the matrix-fullerene solid-state system. Different Lewis acids (Zr(OBut)4, Ti(OBut)4, BF3, SiCl4, and TiCl4) have been used as the catalysts of the epoxy ring opening of (GPTMS) and the polyethylene oxide formation, in three different syntheses, to control and optimize the matrix- fullerene interaction and the optical limiting properties. The microstructure of the hybrid matrix has been studied by Fourier Transform Infra-Red Spectroscopy. UV-vis spectra and optical limiting measurements of the doped materials showed that in the Zr(OBut)4, TiCl4, BF3 derived matrices clustering of fulleropyrrolidine molecules is avoided and optical limiting is obtained. In the Ti(OBut)4, SiCl4, and not epoxy catalyzed derived matrices, instead, the aggregation of fulleropyrrolidines degraded the optical limiting properties. The laser damage threshold in the Zr(OBut)4, TiCl4 and especially BF3 derived matrices was larger than in the other matrices. Moreover, a multilayer system has been fabricated to develop an optical limiting device.

Nonlinear characterization of PbS nanocrystals embedded in sol-gel planar waveguides

Thin silica-titania planar waveguides doped with different concentrations of lead sulfide (10 - 25 mol%) have been prepared by a sol-gel process. It consist of three steps: (a) preparation of a colloidal sol of semiconductor particles; (b) preparation of an alkoxide solution, precursor of the glass- like matrix; (c) mixing of the colloidal sol and the alkoxide solution. Films were deposited on fused silica by dipping and densified for 1 h at 300 degrees Celsius in nitrogen. The mean particle size is 3 nm and the optical absorption edge is situated around 1100 nm. The nonlinear properties have been investigated using degenerated four wave mixing (DFWM) an a nonlinear m-line technique. Different Nd:YAG lasers with pico- and nanosecond pulses at 1064 nm have been used. Depending on the PbS concentration we measured a high negative nonlinear refractive index of n2 equals -3 to -9 10-8 cm2kW for nanosecond pulses (m-lines) and -1 to -10 10-10 cm2/kW for picosecond pulses (m-lines and DFWM). The response time of the nonlinearity is below 30 ps. All observed nonlinear effects are fully reversible and we did not observe any photodarkening. Straight, monomode channel waveguides have been fabricated on theses films.