Christian Palazzesi

Performances of the new high quantum efficiency PMTs in DAMA/LIBRA

New dedicated high quantum efficiency (Q.E.) photomultipliers (PMTs) have been produced by HAMAMATSU company, tested, selected and installed in the DAMA/LIBRA set-up at the Gran Sasso National Laboratory (LNGS) of the I.N.F.N.. In this paper the results obtained in the measurements of various features of these high Q.E. PMTs are reported, and some performances of DAMA/LIBRA in this new configuration are shown.

Self-assembled nanoparticles of functional copolymers for photonic applications

A modified emulsion copolymerization of phenylacetylene (PA) with hydrophilic monomers having different functions, i.e., acrylic acid (AA) and N,N-dimethylpropargylamine (DMPA) respectively, yields functionalized polymeric P(PA-co-AA) and P(PA-co-DMPA) nanoparticles. The systematic investigation on the experimental parameters affecting size, surface charge and polydispersity of the copolymers (initiator concentration, reaction time, cosolvent and PA/comonomer ratios) allows to modulate the nanoparticle physico-chemical properties. Spherical shaped particles with diameters in the range 80-500 nm, low polydispersity (PI values in the range 1.11-1.30) and different surface charge densities, between 0.44 and 2.87 microC/cm(2), have been consistently obtained and characterized by means of Dynamic Light Scattering (DLS), laser Doppler electrophoretic and Scanning Electron Microscopy (SEM) studies. XPS measurements have provided information on the nanoparticles chemical surface structure and suggest that AA and DMPA units are preferentially distributed on the surface of the spheres. The nanospheres self-assemble giving large domains (9.5 x 14.5 microm). Photonic analysis of the self-assembled copolymeric nanoparticles has been performed by means of Spectroscopic Ellipsometry (SE) and Bragg reflection spectroscopy, both of them demonstrating a three-dimensional photonic crystal property of these systems.

Bragg grating optical filters by UV nanoimprinting

Results on an optical waveguide filter operating in the near IR region are reported. The device consists of a hybrid sol-gel-based grating loaded waveguide, obtained through the merging of conventional photolithography and UV-nanoimprinting. Starting from submicrometric gratings, fabricated by electron beam lithography, a soft mould has been produced and the original structures were replicated onto sol-gel photosensitive films. A final photolithographic step allowed the production of grating-loaded channel waveguides. The devices were optically characterized by transmission measurements in the telecom range 1450-1590 nm. The filter extinction ratio is -11 dB and the bandwidth is 1.7 nm.

Integrating superconductive and optical circuits

We have integrated on oxidized silicon wafers superconductive films and Josephson junctions along with sol-gel optical channel waveguides. The fabrication process is carried out in two steps that result to be solid and noninvasive. It is demonstrated that 660nm light, coupled from an optical fiber into the channel sol-gel waveguide, can be directed toward superconducting tunnel junctions whose current-voltage characteristics are affected by the presence of the radiation. The response of the junction biased at various currents as a function of the optical pumping is presented and discussed according to a nonequilibrium superconductivity model.

Evidence of refractive index anisotropy in hybrid sol-gel slab waveguides deposited by spin-coating technique

In this work we report on hybrid organic/inorganic sol-gel based optical waveguides in slab configuration grown both on glass and silicon substrates by spin-coating process. The samples were obtained using Zr(IV)-propoxide as inorganic precursor and 3-glycidoxypropyltrimethoxisilane (GLYMO) as organic component in molar ratio of 3/1. Optical characterization of each layer has been accomplished performing refractive index measurements at different wavelengths in the visible and near infrared regions using an home-made experimental setup developed in our laboratory. Measurements have evidenced a difference between the in-plane and out-of-plane refractive index. We found that the amount of the optical anisotropy depends on the speed of spinning deposition and on the curing temperature. In particular the anisotropy increases with the increasing of speed deposition and with the increasing of curing temperature. Results were also confirmed by spectroscopic ellipsometric measurements. We attributed the optical anisotropy to a preferential orientation of the organic groups of the alkoxysilane precursor (GLYMO) during spin coating deposition.