G. Della Giustina

Active diffraction gratings: Development and tests

We present the realization and characterization of an active spherical diffraction grating with variable radius of curvature to be used in grazing-incidence monochromators. The device consists of a bimorph deformable mirror on the top of which a diffraction grating with laminar profile is realized by UV lithography. The experimental results show that the active grating can optimize the beam focalization of visible wavelengths through its rotation and focus accommodation.

Photopolymerization of hybrid organic/inorganic materials based on nanostructured units for photonic applications

In this work we report on the study of the photopolymerization process in hybrid organic-inorganic films containing photopolymerizable acrylic and methacrylic groups and. The films are doped with a proper photo-initiator for radical polymerization of (meth)acrylic units and are prepared using the sol-gel technique. The photo-initiator is activated by using continuum (single-photon polymerization) or pulsed (two-photon polymerization) laser sources at different wavelengths. After the development of the unexposed regions with a suitable solvent, the photopolymerized structures are observed with microscopy techniques. The effects of the composition of the photopolymerizable mixture, the irradiation parameters (laser power and exposure time) and the external atmosphere in which the photopolymerization is performed are investigated. The fabrication of 3D microstructures using multiphoton absorption processes is a promising technique that involves low amount of incident exposure dose with potentially high spatial resolution.

One- and two-photon pumped soft lithographed DFB laser systems based on semiconductor core-shell quantum dots

In the last years inorganic semiconductor (particularly CdSe and CdS) quantum dots (QDs) have received great attention for their important optical properties. The possibility to tune the emission wavelength, together with their high fluorescence quantum efficiency and photostability, can be exploited in photonic and optoelectronic technological applications. The design of DFB devices, based on QDs as active optical material, leads to the realization of compact laser systems. In this work we explore the use of an inorganic/organic hybrid material composed of CdSe-ZnS semiconductor quantum dots doped into a zirconia sol-gel matrix for optical gain applications. Through the use of soft lithography on a sol-gel germania-silica hybrid, large scale distributed feedback gratings can be created. Used in conjunction with the CdSe-ZnS/ZrO2 hybrids, these gratings can act as microcavities and allow for the realization of true lasing action. The lasing properties within these devices are characterized in the femtosecond regime by both one- and two-photon excitation. From experimental data the value of the optical gain of the core-shell quantum dot samples has been estimated. Moreover, one- and two-photon lasing threshold and stability are reported.

Synthesis of 3-glycidoxypropyltrimethoxysilane-TiO 2 UV-sensitive waveguides

A hybrid organic-inorganic sol-gel material based on 3-(glycidoxypropyl)-trimethoxysilane (GPTMS), an organically modified alkoxide containing an epoxy ring in the organic functional group, and titanium isopropoxide Ti(OPri)4 has been synthesised. The presence of Ti alkoxide is important in order to increase the refractive index and to improve the mechanical and physical properties of the film. A basic catalysis has been used to perform the hydrolysis/condensation reactions of the inorganic network and to preserve the presence of unreacted epoxy rings. The epoxy groups are thus available in the final solid state films for the UV-photopolymerization process. The photopolymerization allows one to increase the refractive index and to pattern the film directly. The modification of the hybrid sol-gel TiO2 matrix microstructure during the thermal treatment and the interaction with the UV light have been investigated by FT-IR and UV-Vis spectroscopies, DTA and TGA thermal analysis. The sol-gel film thickness and roughness have been analyzed by a profilometer: the films possess high optical quality and well controlled thickness, ranging from 500 nm to 2 μm. The refractive index of sol-gel thin films was measured by m-line spectroscopy and ellipsometry. An increase of the refractive index in the range 0,02÷0,1 was achieved, depending on the UV irradiation dose.

One- and Two-Photon Pumped DFB Laser Based on Semiconductor Quantum Dots Embedded in a Sol-Gel Matrix

In the last years inorganic semiconductor (CdSe and CdS) quantum dots (QDs) have received great attention for their important optical properties: the design of DFB devices, based on QDs as active optical material, leads to the realization of compact laser systems.

Transmittance of hybrid sol-gel materials in the THz region

We report on the absorption properties of hybrid sol-gel materials based on the 3-glycidoxypropyltrymethoxysilane (GPTMS) precursor in the spectral region 0.5–7 THz. THz transmission properties of such materials are quite good and, even if not comparable with the most transparent polymers, still their chemico-physical, structural, and electro-optical properties make them attractive alternative systems for applications in the THz field. An attempt to explain the relationship between compositional and structural characteristics of the investigated materials with their transmission behaviour is presented.