S. C. Zilio

Excited State Dynamics of meso-Tetra(sulphonatophenyl) Metalloporphyrins

The excited state dynamics of Zn2+, Fe3+, and Mn3+ meso-tetra(sulfonatophenyl) porphyrin complexes were investigated with a Z-scan technique at 532 nm using 70 ps and 120 fs single pulses and 200 ns pulse trains of a Q-switched and mode locked laser. We determined the characteristic interconversion and intersystem crossing times, quantum yields of the excited S1 state, and S1 --> Sn and T1 --> Tn transition cross-sections. The ground state cross-sections were obtained using UV-vis absorption spectroscopy, and a five-energy-level diagram was used to yield the photophysical parameters mentioned previously.

Influence of self-focusing of ultrashort laser pulses on optical third-harmonic generation at interfaces

We report on the third-harmonic generation of femtosecond laser pulses at interfaces. We measured slabs of different types of optical glasses and demonstrated that the asymmetric intensity profile observed for a tightly focused beam can be explained by self-focusing effects.

Broadband third-harmonic generation on interfaces using femtosecond pulses

We report on third-harmonic generation (THG) in optical materials using femtosecond pulses and Z-scan method. Here we have played with beam focusing parameters and, in this way, we could track the THG signal at function of Rayleigh ranges. We observed that the femtosecond pulse has broadband spectrum and such property also affects the thirdharmonic (TH) spectrum. In this experiment we were able to distinguish the contribution of bulk and interface on the THG by measuring the intensity and spectral profile of the TH signal.

New simple method for measuring nonlinear polarization ellipse rotation with high precision using a dual-phase lock-in

The measurements of nonlinear ellipse rotation (NER) can be very helpful to determine the magnitude, as well, the origin of the nonlinearity. As it is known, NER is related to particular component of the third-order nonlinear susceptibility which can be different from other nonlinear effects. In this way, here we propose a new method to improve the measuring precision of the NER angle using a dual phase lock-in. We also did a well known Z-scan measurement which provides the nonlinear refractive index to give support to our results. Using these two measurements, we could study several materials nonlinearity with different origin and we could reveal the tensor nature of the refractive nonlinearities. Material with thermal, molecular orientation and nonresonant electronic origins could be easily distinguished by those techniques.

High-resolution nonlinear ellipse rotation measurements for 3D microscopy

Nonlinear optical effects have been widely explored for microscopy due to the possibility of three-dimension (3D) image acquisition. Harmonic generation and nonlinear absorption, for instance, were used for this purpose. Each nonlinear effect has its own characteristic, complexity, type of contrast, advantage and disadvantage, etc. Recently, we developed a new simple and sensitive method for measuring nonlinear ellipse rotation (NER) using a dual-phase lock-in amplifier, which could be successfully applied for measuring local nonlinearity distribution on a sample and, consequently, the image acquisition. The NER is a particular refractive nonlinear effect which appears when strong elliptical polarized laser beam propagates along one nonlinear material. It is type of refractive Kerr nonlinearity similar to self-focalization responsible for the signal in the Z-scan technique. The self-focalization is one of the most important refractive effects, but it cannot be used for image acquisition. On the other hand, NER does. Furthermore, such refractive nonlinearities signal can be very strong and serves as a new contrast for nonlinear microscopy.

Study of broadband femtosecond third-harmonic generation in organic solvent-fused silica interfaces

We report measurements on third-order nonlinear optical properties using the spectrum and the magnitude of the third-harmonic generated by femtosecond laser pulses in transparent materials interfaces.

Optics Properties Of X-ray Irradiated L-Threonine Crystals

In this work we study optical properties of L-threonine crystals with stables radicals induced by X-ray irradiation. We have measured the absorption spectra, the index of refraction, the second-harmonic generation of irradiated and not-irradiated materials.

Measuring optical nonlinearities using a heterodyne Z-Scan technique

We present a heterodyne Z-scan technique to obtain resonant nonlinearities (n2) of Kerr-like media. From phase measurements we determine both signal and magnitude of n2. Results are presented for a ruby sample.

Measurement and modeling of two-photon absorption spectrum in azoaromatic compounds

This work reports a systematic study on the degenerate two-photon absorption spectrum of azo-aromatic compounds, using the Z-scan technique with femtosecond pulses. The nonlinear spectra obtained were modeled using a perturbation theory treatment.

Nonlinear absorption spectrum in perylene derivatives

Knowledge about nonlinear absorption spectra of materials used in photonic devices is of paramount importance in determining their optimum operation wavelengths. In this work, we have investigated the two-photon absorption (2PA) degenerate cross-section spectrum for perylene derivatives using the Z-scan technique with femtosecond laser pulses. All perylene derivatives studied present large 2PA cross-sections, only comparable to the best ones reported in the literature. The results achieved in the present investigation indicate perylene derivatives as promising materials for two-photon applications.