Optical limiting and non linear optical properties of fullerene derivatives embedded in hybrid sol-gel glasses

Non linear optical properties of pyrrolidino-fullerenes in sol-gel matrix have been investigated for Optical Limiting (OL) applications, The fullerene functionalization increases the solubility in polar solvent and allows the preparation of solid materials via sol-gel method. It also extends the absorption of fullerenes to the red spectral region, where the maximum of the triplet to triplet absorption spectrum is located and, as a result, the Reverese Saturable Absorption (RSA) mechanism is enhanced, The use of the sol-gel method allows the preparation of samples with controlled thickness, with very good linear and non linear optical properties and with high damage fluences. This is useful to design and prepare a bottleneck structure, in order to optimize a laser protection device. The test of the non-linear optical properties of sol-gel samples containing fullerene derivatives has been made by optical limiting and Z-scan measurements and by comparing the experimental data with the calculated RSA behavior. Fullerene derivatives show good optical limiting performances in the red spectral region, better than fullerene. The pyrrolidino-fullerenes in sol-gel samples still show the same performances as solution samples. The comparison of the experimental data with the theoretical OL curves indicates that RSA is the predominant OL behavior, especially at 690 nm, but other different mechanisms, like non linear scattering, may contribute and are being considered in refining our theoretical model. The control of the propagation beam geometry is one of the critical point for OL measurements as well as for the optimal design of a protecting device.