J. J. Rodrigues

Optical properties of L-threonine crystals

Abstract Second- and third-order optical nonlinearities of L-threonine amino acid crystals grown from aqueous solution are investigated in this work. The absorption spectra indicate a good transparency between 250 and 1500 nm. Refractive indices were measured as a function of temperature and wavelength, allowing the determination of the thermo-optic and Sellmeier equation coefficients. Phase-matching curves for second harmonic generation from radiation at 1.064 μm were obtained. The conversion efficiency was measured along the entire phase-matching loci and its maximum value was found to be comparable to that of KDP. The nonlinear refractive index n 2 , measured through the Z-scan technique with femtosecond pulses, is of the order of 10 −20 m 2 /W.

Two-photon absorption in azoaromatic compounds

Abstract We report on the two-photon absorption (2PA) cross-section for eight azoaromatic compounds in dimethyl sulfoxide solutions, using the Z-scan technique with femtosecond laser pulses at 775 nm. The 2PA cross-sections of these molecules are of the order of (1–6)×10 −50 cm 4 s photon −1 . A correlation was established between the molecular structure and the two-photon absorption process, which makes it possible to develop molecular design strategies to create structures with suitable two-photon absorption coefficients.

Femtosecond Z-scan measurements of nonlinear refraction in amino acid solutions

Abstract We report an investigation of third-order optical nonlinearities in several amino acid solutions using the Z-scan technique with femtosecond laser pulses at 775 nm. The amino acid solutions studied are usually employed for crystal growth, which can be used for ultrashort-pulse second-harmonic generation. The nonlinear refractive index n2 in these aqueous solutions has been determined to be in the range from 10−17 to 10−16 cm2/W (second hyperpolaribality γ ranging from 0.9×10−36 to 3.3×10−36 esu). No two-photon absorption was observed. The experimental second molecular hyperpolarizabilities obtained for each amino acid are in good agreement with semi-empirical AM1 calculations.

Dynamic saturable optical nonlinearities in free base tetrapyridylporphyrin

Dynamic optical nonlinearities in free base tetrapyridylporphyrin (H2TPyP) solutions were investigated at 532 nm with the Z-scan technique. We observed a reverse saturable absorption process that was found to have a fast contribution related to the singlet population and a slow accumulative contribution arising from the triplet population. The optical excitations and subsequent relaxations can be interpreted with a five-energy-level diagram that allows determination of the excited states photophysical parameters such as triplet and singlet absorption cross-sections and the intersystem crossing time.

Measuring milk fat content by random laser emission

The luminescence spectra of milk containing rhodamine 6G are shown to exhibit typical signatures of random lasing when excited with 532 nm laser pulses. Experiments carried out on whole and skim forms of two commercial brands of UHT milk, with fat volume concentrations ranging from 0 to 4%, presented lasing threshold values dependent on the fat concentration, suggesting that a random laser technique can be developed to monitor such important parameter.

The influence of pH in nonresonant third-order nonlinearities of amino acid solutions

Abstract We report on the use of the Z -scan technique with femtosecond pulses at 775 nm to investigate the electronic charge delocalization in l -arginine, l -proline and l -serine amino acids. We have observed a variation in the nonresonant nonlinear transmittance with the pH, which reflects the variation in the relative concentration of the cationic and anionic forms and, consequently, the electronic charge delocalization. For l -serine, for instance, at a pH around 6.0 the n 2 rises to its maximum value corresponding to the one expected for the maximum concentration of the zwitterionic form. A good correspondence between the measured nonlinear transmittance variation and the titration curve was observed for the three amino acid samples, in the pH range studied. The n 2 values measured range from 10 −17 to 10 −16 cm 2 /W for pH varying from about 2 to 9.2.

A Comparative Study of Er3+, Er3+-Eu3+, Er3+-Tb3+, and Er3+-Eu3+-Tb3+Codoped Y2O3Nanoparticles as Optical Heaters

Fluorescence intensity ratio (FIR) technique, based on the thermal coupling of and energy levels of erbium ions, was used to study the optical heating behavior of rare earth doped yttrium oxide nanophosphors (Y2O3:Er3Fluorescence intensity ratio (FIR) technique, based on the thermal coupling of 2H11/2 and 4S3/2 energy levels of erbium ions, was used to study the optical heating behavior of rare earth doped yttrium oxide nanophosphors (Y2O3:Er3+, Y2O3:Er3+-Eu3+, Y2O3:Er3+-Tb3+, and Y2O3:Er3+-Eu3+-Tb3+) synthesized via PVA-assisted sol-gel route. The samples were optically heated by an 800 nm CW diode laser, while the upconverted green emissions were used to measure their temperatures in real time. The experimental results indicate that the studied nanoparticles are promising candidates to applications such as photothermal treatments and hyperthermia.

Spectroscopic and electrochemical study of CdTe nanocrystals capped with thiol mixtures

Here we report the aqueous synthesis of CdTe nanocrystals capped with 3-mercaptopropionic acid (MPA) and the evaluation of the effect of mixing different thiols with MPA on the spectroscopic and electrochemical properties. Additional ligands were cysteine (CYS) and glutathione (GSH). CYS and GSH produce opposite effects on the photoluminescence quantum yield (QY) with a decrease and increase in QY in comparison to MPA, respectively. All samples exhibited monoexponential photoluminescence decays indicating the presence of high-quality nanocrystals. Electrochemical measurements evidenced the presence of several redox peaks and allowed the calculation of the electrochemical band gaps, which were in agreement with the values estimated from absorption spectra and reflected differences in nanocrystal size.

A comparative study of Er 3+ , Er 3+ -Eu 3+ , Er 3+ -Tb 3+ , and Er 3+ -Eu 3+ -Tb 3+ codoped Y 2 O 3 nanoparticles as optical heaters

Fluorescence intensity ratio (FIR) technique, based on the thermal coupling of and energy levels of erbium ions, was used to study the optical heating behavior of rare earth doped yttrium oxide nanophosphors (Y2O3:Er3Fluorescence intensity ratio (FIR) technique, based on the thermal coupling of 2H11/2 and 4S3/2 energy levels of erbium ions, was used to study the optical heating behavior of rare earth doped yttrium oxide nanophosphors (Y2O3:Er3+, Y2O3:Er3+-Eu3+, Y2O3:Er3+-Tb3+, and Y2O3:Er3+-Eu3+-Tb3+) synthesized via PVA-assisted sol-gel route. The samples were optically heated by an 800 nm CW diode laser, while the upconverted green emissions were used to measure their temperatures in real time. The experimental results indicate that the studied nanoparticles are promising candidates to applications such as photothermal treatments and hyperthermia.

A Comparative Study of Er3

Fluorescence intensity ratio (FIR) technique, based on the thermal coupling of and energy levels of erbium ions, was used to study the optical heating behavior of rare earth doped yttrium oxide nanophosphors (Y2O3:Er3Fluorescence intensity ratio (FIR) technique, based on the thermal coupling of 2H11/2 and 4S3/2 energy levels of erbium ions, was used to study the optical heating behavior of rare earth doped yttrium oxide nanophosphors (Y2O3:Er3+, Y2O3:Er3+-Eu3+, Y2O3:Er3+-Tb3+, and Y2O3:Er3+-Eu3+-Tb3+) synthesized via PVA-assisted sol-gel route. The samples were optically heated by an 800 nm CW diode laser, while the upconverted green emissions were used to measure their temperatures in real time. The experimental results indicate that the studied nanoparticles are promising candidates to applications such as photothermal treatments and hyperthermia.