CdS quantum dots (QDs) embedded in a phosphate glass matrix were investigated. The time-resolved Z-scan technique was used to determine the nonlinear refraction and absorption for different concentrations of CdS QDs. The results indicate that the nonlinear absorption presents a reverse saturable character, which is a desirable feature in the design of optical limiting devices. In addition, strong experimental evidence that the main contribution onto the refractive index variation is not of thermal origin was found. The observed variation presents a character similar to an electronic-like effect. These evidences are supported by numerical simulations.
The aim of this work is the use of the Z-scan technique to determine the nonlinear refraction and nonlinear absorption of phosphate glass doped with CdS. This glass matrix, termed as PANK (P<sub>2</sub>O<sub>5</sub>-Al<sub>2</sub>O<sub>3</sub>-Na<sub>2</sub>O-K<sub>2</sub>O), was doped with 1, 2 and 3 % of CdS concentration. The quantum dots (QDs) are materials extensively investigated in the last years for their special physical properties associated to discrete energetic levels.
The spectroscopic properties of rare earth ions in many different hosts have been investigated, including surveys of Nd<sup>3+</sup> in silicate, phosphate, fluorophosphates and fluoride glasses. Some of the thermal-optical properties of materials are influenced by temperature change, such as thermal diffusivity, specific heat and luminescence quantum efficiency. In this work the luminescence quantum efficiency of PANK: Nd<sup>3+</sup>, as a function of temperature (80- 480 K), was investigated using the normalized lifetime thermal lens technique. This system presents high quantum efficiency at low Nd<sup>3+</sup> concentration and at ambient temperature, ~100%, which decrease as temperature increase. Below room temperature the effects are not in accord with the maximum value of η, which must be unity.
In this work optical spectroscopic characterization was performed in a Er-doped phosphate glass matrix PAN (P2O5-Al2O3-Na2CO3). Due to its high phonon energy, only the 1550 nm emission band was observed. Therefore, we have applied the normalized lifetime thermal lens technique in order to determine the luminescence quantum efficiency of this emission. These results were compared with that obtained with the standard Judd-Ofelt calculations. Besides absorption spectra, emission spectra as also obtained. Therefore, the gain coefficient spectra could be evaluated for different population inversions. Finally, figures of merit for the optical amplifiers were estimated and compared with others Er-doped materials.
In this work, we have used a Ti<sup>3+</sup>:Safira laser tuned at 803nm to performed time-resolved measurements using the Z-scan technique to characterize the nonlinear optical properties of phosphate glasses. The glass matrices, labeled PAN (P<sub>2</sub>O<sub>5</sub>-Al<sub>2</sub>O<sub>3</sub>-Na<sub>2</sub>CO<sub>3</sub>) and PANK (P<sub>2</sub>O<sub>5</sub>-Al<sub>2</sub>O<sub>3</sub>- Na<sub>2</sub>O-K<sub>2</sub>O), were doped with increasing Nd<sup>3+</sup> concentration, ranging from 0.5 to 5 wt%. For both systems, we have seen that the optical nonlinearity has a linear dependence with the doping ion concentration. Therefore, we propose a new approach to obtain the parameters Δα and Δσ. All results obtained are in good agreement with others found in the literature.
Thermal-Lens (TL) for fluorescence quantum efficiency (η) characterizations in a new phosphate glass matrix doped
with Nd<sup>3+</sup> were performed. η studies were accomplish in function of Nd<sup>3+</sup> concentrations (0.5-3 x 10<sup>20</sup> ions/cm<sup>3</sup>). In addition, fluorescence quenching was studied by measuring the concentration dependence of the fluorescence lifetime. The results obtained by TL and fluorescence lifetime techniques are in good agreement, and corroborate with the theory for an energy transfer process involving a pair of ions, in which the main process occurring is cross-relaxation (CR).
The quantum dots (QDs) for use in nanobiotechnology trials should be thermodynamically stable and have
homogeneous dispersion, high radiative quantum efficiency (η), a very broad absorption spectrum, low levels of
nonspecific links to biological compounds and, most importantly, stability in aqueous media. Recently, a new class of
CdSe QDs called magic-sized quantum dots (MSQDs), with sizes from 1 to 2 nm and well-defined structures, has
attracted considerable attention because of its novel physical properties. The present work reports the thermo-optical
properties of CdSe/CdS MSQDs and CdSe/ZnS QDs suspended in aqueous solutions. Absolute nonradiative quantum
efficiency (φ) and η values were determined applying two techniques: the well-known Thermal Lens (TL) technique
and an alternative method called thermal spatial self-phase modulation (TSPM) technique.
Thermal Lens (TL) and spectroscopic characterizations were performed in CdSe/ZnS core-shell quantum dots (QDs)
embedded into two commercial dental resin composites. The thermal-optical studies were performed in CdSe/ZnS QDs
(core size Φ= 4.1 nm) and PMMA-encapsulated CdSe/ZnS (Φ= 3.7 nm) embedded in restorative dental resins at
concentration of 0.025 and 0.42 % in mass, respectively. The thermal diffusivity (D) results are characteristics of the
dental resin composites studied. Photoacoustic (PA) technique results for the dental resin composites support the TL
A variety of effects is attributed to the photo stimulation of tissues, such as improved healing of ulcers, analgesic and anti-inflammatory effects, stimulation of the proliferation of cells of different origins and stimulation of bone repair. Some investigations that make qualitative evaluations, like wound healing and evaluation of pain and edema, can be conducted in human subjects. However, deeper investigations on the mechanisms of action of the light stimulus and other quantitative works that requires biopsies or destructive analysis has to be carried out in animal models or in cell
cultures. In this work, we propose the use of planarians as a model to study laser-tissue interaction. Contrasting with cell cultures and unicellular organisms, planarians are among the simplest organism having tissue layers, central nerve system, digestive and excretory system that might have been platforms for the evolution of the complex and highly organized tissues and organs found in higher organisms. For the present study, 685 nm laser radiation was employed.
Planarians were cut transversally, in a plane posterior to the auricles. The body fragments were left to regenerate and the proliferation dynamics of stem cells was studied by using histological analysis. Maximum cell count was obtained for the laser treated group at the 4<sup>th</sup> experimental day. At that experimental time, we also had the largest difference between the irradiated and the non-irradiated control group. We concluded that the studied flatworm could be an interesting animal model for in vivo studies of laser-tissue interactions.
Thermal Lens (TL) and spectroscopic characterizations were performed in CdSe/ZnS core-shell nanoparticles
embedded into the underlying polymethyl methacrylate (PMMA) dissolved in chloroform (CHCl<sub>3</sub>). TL measurements
were accomplished in function of the CdSe/ZnS quantum-dot concentration (12-60 mg/ml). The average value obtained
for the thermal diffusivity was (0.85 ± 0.02) x 10<sup>-3</sup> cm<sup>2</sup>/s. The absolute nonradiative quantum efficiency φ and the
fluorescence quantum efficiency η were determined by the TL method. Higher values of φ were obtained with the
increase of the core-shell nanoparticles concentrations in PMMA-chloroform solutions. These results are in agreement
with the behavior of fluorescence spectra that decrease with CdSe/ZnS concentration increase.
Thermal Lens (TL) and spectroscopic characterizations were performed in 70TeO<sub>2</sub>-19WO<sub>3</sub>-7Na<sub>2</sub>O-4Nb<sub>2</sub>O<sub>5</sub> (mol%) tellurite glasses. TL measurements were accomplished in Er<sup>3+</sup> /Tm<sup>3+</sup> co-doped tellurite glasses in function of the Tm<sub>2</sub>O<sub>3</sub> concentration (0.4-1.6 x10<sup>20</sup> ions/cm<sup>3</sup>). Fluorescence spectra at 488 nm showed that Er<sup>3+</sup> /Tm<sup>3+</sup> co-doped tellurite glasses present several emission bands between (500-1800) nm. However, the more intense emission bands correspond to the Tm<sup>3+</sup> and Tm<sup>3+</sup> transitions (<sup>4</sup>I<sub>13/2</sub> → <sup>4</sup>I<sub>15/2</sub> and <sup>3</sup>F<sub>4</sub> → <sup>3</sup>H<sub>6</sub>), respectively. The absolute nonradiative quantum efficiency (φ) was determined by TL method. Higher values of φ were obtained with the increase of Tm<sub>2</sub>O<sub>3</sub> concentration inside of the Er<sup>3+</sup>/Tm<sup>3+</sup> co-doped tellurite glasses. These results are corroborated by the Judd-Ofelt calculations.
We report the observation of conical emission induced by cross-phase-modulation when a strong beam copropagates with a weak beam through dimethylsulfoxide. Laser beams at 1064 nm and 597 nm, in the transparency window of the material, were used. The phenomenon is understood in terms of a nonlinear spatial modulation of the refractive index.
In nonlinear optics, the Gaussian beam intensity profile, I(r) exp(-2r<SUP>2</SUP>/w<SUP>2</SUP>) generates a refractive index profile (Delta) n(r), and consequently a phase profile. Depending on the magnitude of the phase profile, rings structures can be observed in the beam far field intensity profile, the so-called Transverse Self Phase Modulation effect. In this work, we calculated these rings formation due to thermal and Kerr non linearities, using the Fresnel- Kirchhoff diffraction integral. In the case of Kerr nonlinearity, the refractive index profile is also Gaussian since n(r) equals n<SUB>0</SUB> + n<SUB>2</SUB>I(r). However, due to the effect of heat diffusion, in the case of thermal nonlinearity the refractive index profile is broader than I(r).
In this work we applied the Thermal Lens (LT) technique to determine the upconversion parameter for Cr<SUP>3+</SUP>:LiSrAlF<SUB>6</SUB>, Cr<SUP>3+</SUP>:LiSrGaF<SUB>6</SUB>, Cr<SUP>3+</SUP>:SrAlF<SUB>5</SUB> and Nd<SUP>3+</SUP>:ZBLAN. The measures for the Cr<SUP>3+</SUP> doped fluorides were accomplished at 15 degrees C to eliminate the suppression effect due to temperature and upon excitation in the cw regime. We used Ar<SUP>+</SUP> laser and dye laser radiation for the Cr<SUP>3+</SUP> doped crystals and 514 nm and 796.7 nm for the Nd<SUP>3+</SUP> doped glasses. We observed a nonlinear increase of the TL signal with excitation power, characterizing a fluorescence quantum efficiency decrease that was attributed to the Auger effect. A theoretical model was developed to obtain (gamma) from the TL data.
Fluorescence quantum efficiency, defined as the ratio between the radiative decay and the total decay times, is an important optical property of fluorescent materials. There are two important processes responsible to reduce the upper- state population and consequently (eta) in fluoride crystals: the fluorescence thermal quenching and the upconversion. In this work the results of (eta) in function of temperature for Cr<SUP>3+</SUP>-doped fluoride crystals were obtained with the thermal lens technique. Remember that the excited state lifetime is given by radiative and nonradiative parts, an important particular feature in these fluoride crystals is the strong temperature.