A.G. Bezerra

Investigation of picosecond optical nonlinearity in porphyrin metal complexes derivatives

Abstract Porphyrin metal complex derivatives were experimentally studied using the Z -scan technique and the optical Kerr gate method with picosecond pulses at 532 nm. The sign and magnitude of the nonlinear refraction and nonlinear absorption were determined for a negatively charged meso -tetrakis( p -sulfonatophenyl)porphyrin (TPPS 4 ) and a positively charged meso -tetrakis(4- N -methyl-pyridiniumyl)porphyrin (TMPyP) in their free-base forms and their Fe(III) and Mn(III) complexes. The results were phenomenologically understood and the origin of the nonlinearity was inferred.

Blue light emission in thulium doped silica-on-silicon waveguides

Abstract We report the experimental observation of up-conversion in an integrated silica-on-silicon waveguide. Blue light at 455 nm and 475 nm was observed. In addition to the strong blue emission near infrared (∼ 800 nm), visible (648 nm) and UV (366 nm) lines were also detected. We investigated the excitation mechanisms by using different pumping wavelengths.

Mesoionic rings as third-order non-linear optical materials

Abstract A study of the non-linear refractive index ( n 2 ) and the non-linear absorption coefficient ( α 2 ) of molecules containing mesoionic rings in solution has been carried out using the Z-scan technique with 70 ps at 532 nm. The second molecular hyperpolarizabilities, γ , were inferred and the experimental results are in a good qualitative agreement with our semi-empirical AM1–TDHF calculations. Optical Kerr gate measurements with 60 fs pulses at 800 nm allowed us to identify an ultra-fast response time for the third-order non-linearity. These results indicate that mesoionic rings are promising materials for photonic applications.

Molecular hyperpolarizabilities of retinal derivatives

We report measurements of the third-order optical susceptibilities of 13-cis and all-trans retinal derivatives in chloroform liquid solutions using the Z scan and the optical Kerr gate techniques, with laser pulses of 70 ps and 60 fs, at 532 and 800 nm, respectively. The corresponding second hyperpolarizabilities of those molecules are estimated and the results compared to those obtained from semiempirical time-dependent Hartree–Fock calculations. The observed trends for the values of the nonlinear response are explained in terms of the π electron delocalization along the polyenic chain of the molecules.

Third-order nonlinear optical properties of undoped polyaniline solutions and films probed at 532 nm

The third-order nonlinear optical properties of polyaniline (PANI) solutions and films were investigated at 532 nm by use of Z-scan, power limiting, and optical Kerr gate techniques. The polymers studied were the undoped partially oxidized (emeraldine base) and fully reduced (leucoemeraldine base) forms of PANI. Our results demonstrate that the leucoemeraldine base is more suitable for use in devices such as all-optical switches and optical power limiters operating at 532 nm. The worse performance of the emeraldine base is due to the presence of defects inside the bandgap of the polymer.

Exploitation of the Z-scan technique as a method to optically probe pK(a) in organic materials: application to porphyrin derivatives.

We demonstrate the use of the Z-scan technique as a method to measure a chemical parameter, the pK(a) value, that characterizes the equilibrium constant in acid-base reactions. The measurements were performed with picosecond pulses at 532 nm in Fe(III)-meso-tetrakis(4-N-methyl-pyridyl) porphyrin. The results were compared with linear absorption measurements and electron paramagnetic resonance, the usual techniques employed to determine pK(a) values in aqueous solutions, and showed excellent agreement.

Nonlinear optical properties of organic materials

The second-order hyperpolarizabilities of two groups of organic materials, retinal derivatives and mesoionic compounds, are obtained through measurements of nonlinear optical susceptibilities. The Z-scan technique was employed to characterize the sign and magnitude of the third-order nonlinear optical coefficient, whilst the Kerr Gate method was employed to infer the response time of the nonlinearity with 60 fs resolution. From these measurements, supported by quantum chemical theoretical calculations, the origin of the nonlinearity was determined for both materials.

Effects of pH and ionic strength on the structure and spectroscopic properties of Fe(III) complex porphyrin in aqueous solutions

Summary form only given. The porphyrin iron complexes are important components of nature involved in various biological processes. We report on the studies of the effect of pH and ionic strength on the equilibrium of different forms of the Fe(lII) complex of mesotetrakis(4-N-methyl-pyridiniomyl) porphyrin Fe(II)TmPyP or FeTMP in aqueous solutions by linear optical absorption, the Z-scan technique and EPR. The experimental results of Z-scan and electroparamagnetic resonance (EPR) are compared with semi-empirical quantum chemical calculations (ZINDO).

First- and second-order optical hyperpolarizabilities of polyaniline in solutions

Summary form only given. The class of materials known as conjugated polymers (CP) has attracted great attention due to its optical and semiconductor properties. Among CPs, polyaniline (PANI) has been found to be a unique material that presents a reversibility character of its conductivity. For example, upon redox and protonation it is possible to change the polymer from an insulating (leucoemeraldine) form, to a conducting polymer (emeraldine salt). Concerning its optical properties, PANI has been attracted interest because of its fast response time. Spectroscopic measurements have been performed of the first (/spl beta/) and second (/spl gamma/) hyperpolarizabilities of PANI dissolved in solutions of dimethyl sulfoxide (DMSO). We measured /spl beta/ and /spl gamma/ in various degrees of oxidation and protonation: emeraldine base (EB), emeraldine salt (ES), leucoemeraldine base (LB) and leucoemeraldine salt (LS). The spectroscopic techniques used to measure /spl beta/ and /spl gamma/ were hyper-Rayleigh scattering (HRS) and Z-scan, respectively.

Conformational dependence and femtosecond response of the third-order nonlinearity in retinal derivatives

Summary form only given. The nonlinear optical properties of organic materials have been thoroughly studied with views to the basic understanding of its physical origin as well as to their application in photonic devices. It is the /spl pi/-electron delocalization in organic molecules that leads to high molecular hyperpolarizabilities and large nonlinear susceptibilities. Retinal, a molecular structure related to vitamin A, and its derivatives belong to a family of molecules that plays a prevalent role in photobiological processes. For instance, the primary event of vision mechanism in animals is associated to the cis to trans isomerization of the retinal molecule. Tote and coworkers (1994) have predicted that this conformational change should be accompanied by a noticeable change in the hyperpolarizability of the molecules since the more linear character of the trans conformation should favor the delocalization of the /spl pi/-electrons in the conjugated system. We used the Z-scan technique to determine the nonlinear refractive index and the nonlinear absorption coefficient.