Tommaso Baldacchini

Femtosecond laser waveguide micromachining of PMMA films with azoaromatic chromophores

We report on the femtosecond-laser micromachining of poly(methyl methacrylate) (PMMA) films doped with nonlinear azoaromatic chromophores: Disperse Red 1, Disperse Red 13 and Disperse Orange 3. We study the conditions for controlling chromophore degradation during the micromachining of PMMA doped with each chromophore. Furthermore, we successfully used fs-micromachining to fabricate optical waveguides within a bulk sample of PMMA doped with these azochromophores.

Reversible birefringence in microstructures fabricated by two-photon absorption polymerization

This paper reports the fabrication of birefringent microstructures using two-photon absorption polymerization. The birefringence is caused by a light-driven molecular orientation of azoaromatic molecules (Disperse Red 13) upon excitation with an Ar+ laser at 514.5nm. For an azoaromatic dye content of 1% by weight, we obtain a birefringence of 5×10−5. This birefringence can be completely erased by overwriting the test spot with circularly polarized laser light or by heating the sample. Our results open the door to the development of alternative applications in optical data storage, waveguiding, and optical circuitry.

Emission Intensity and Degradation Processes of Alq3 Films

Emission Intensity and Degradation Processes of Alq3 Films Giuseppe Baldacchini,* Tommaso Baldacchini, Angelo Pace, and Ramchandra Balaji Pode ENEA, Frascati Research Center, Department of Advanced Physical Technologies, 00044 Frascati, Roma, Italy Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA Department of Physics, Nagpur University, Nagpur 440 010, India

Photoluminescence and Morphology of Alq3 Films and Four-Components Model

Recently, it has been shown that the photoluminescence (PL) of one Alq 3 film decays in air with four different constant times and spectral features, implying the existence of four different components of molecular aggregation. Now the same behavior has been confirmed by measuring in open and dry air the PL of films fabricated in different physical conditions, which influence to various degrees the amplitude of the components. Moreover, the constant times are longer in Alq 3 films kept in the external dry environment than in the normal atmosphere. The implications of these experimental observations for the morphology of the films is discussed in the light of a phenomenological approach which has been called the four-components model.

Photoluminescence of Alq3 Stabilized by a Phenolic Compound

Over the last 10 years, several organic compounds have been used to realize efficient electroluminescent devices, organic light-emitting diodes (OLED), which have now become competitive with the well-known and older inorganic semiconductor diodes, LED. Among these new luminescent compounds, the metallorganic molecule Alq 3 has an efficient emission band in the green region of the electromagnetic spectrum, and is easily handled. However, OLEDs realized with Alq 3 and other organic compounds display a lifetime defined as the time required by the emission to reduce by half its initial value, equal to about 5000 h, which is considered to be too short for practical applications. Several studies have been performed on organic compounds to understand their degradation, which has been ascribed to both intrinsic and extrinsic effects; among the latter, exposition to atmospheric agents is considered to be very important. Simple experiments have been made to verify the oxidation processes and the possibility to halt or retard them by using appropriate chemical compounds. Butylated hydroxytoluene, a molecule belonging to the big family of phenols, proved to be effective in preserving the photoluminescence of Alq 3 films. Our results support the idea that phenols, which are known to be strong antioxidant products, can increase the lifetime of OLEDs realized with small organic molecules and polymers.

Why Annealing Processes Affect the Optical Properties of Alq3 Films and OLEDs

Organic light emitting diodes, OLEDs, have been so much improved in the last two decades that they are being currently used in commercial applications for displays and lighting. Among many improving technologies, thermal treatments affect greatly their performances. In case the small molecule Alq3 is the active material, it was never understood why and how the temperature could have played such an important role. Now, we have discovered that such molecules tend to aggregate themselves in morphological states which are very much sensible to annealing processes, with the result of improved emission efficiency and lifetime of Alq3 thin films. Moreover, the latter ones are described by a four components model, FCM, which has been validated by degradation experiments during 6 years, a world record in its own.

Reversible birefringence in microstructures fabricated by two-photon polymerization

We use two-photon absorption polymerization to fabricate optically active microstructures that exhibit optically-induced birefringence and dichroism. Our results open the door to new applications in data storage, waveguides and optical circuitry.

A novel photoinitiator for microfabrication via two-photon polymerization

We measured the two-photon absorption cross-section of Lucirin TPO-L and fabricated complex microstructures using it in acrylate resin. Using quantum chemistry calculations, we relate the nonlinear optical properties of the photoinitiator to its molecular structure.