Márcio A. R. C. Alencar

Er3+-doped BaTiO3 nanocrystals for thermometry: Influence of nanoenvironment on the sensitivity of a fluorescence based temperature sensor

Frequency upconverted emissions centered at 526 and 547 nm from two thermodynamically coupled excited states of Er3+ doped in BaTiO3 nanocrystals were recorded in the temperature range from 322 to 466 K using a diode laser emitting at 980 nm as the excitation source. The ensemble measurements of the fluorescence intensity ratio (FIR) of the signals at 526 and 547 nm as a function of the temperature showed that the sensitivity (the rate in which the FIR changes with the temperature) of such sensor depends on the size of the nanocrystal. This is explained taking into consideration modifications of nonraditive relaxation mechanisms with the size of the nanocrystals.Frequency upconverted emissions centered at 526 and 547 nm from two thermodynamically coupled excited states of Er3+ doped in BaTiO3 nanocrystals were recorded in the temperature range from 322 to 466 K using a diode laser emitting at 980 nm as the excitation source. The ensemble measurements of the fluorescence intensity ratio (FIR) of the signals at 526 and 547 nm as a function of the temperature showed that the sensitivity (the rate in which the FIR changes with the temperature) of such sensor depends on the size of the nanocrystal. This is explained taking into consideration modifications of nonraditive relaxation mechanisms with the size of the nanocrystals.

Ultrafast dynamics of mesoionic liquid solutions studied with incoherent light

Optical Kerr shutter (OKS) measurements were performed in a solution of a mesoionic compound (MIC) in dimethylsulfoxide using 10 ns pulses of broadband noisy light with a coherence time of 160 fs. The results show a light induced birefringence with two main components: an instantaneous one, which follows the laser coherence time, and a sub-picosecond component, with a characteristic time of 560 fs, which is attributed to the birefringence decay due to molecular interactions.

Surface plasmon assisted directional laserlike emission from a highly scattering dye doped polymeric gain medium

Summary form only given. The first observation of laserlike emission from a scattering medium consisting of TiO/sub 2/ particles in a dye solution was reported a few years ago. The emission from such system, which was named laser paint (LP) exhibits the characteristics of a multimode laser oscillator, although no resonant cavity is used. The phenomenon has been well studied but the LP-emission, which is almost spatially isotropic, would be more useful for applications if a scheme could be developed for obtaining directional emission. In this communication we report the first observation of quasi-directional LP-emission. The experiments were performed with a sample of a PMMA flat disc doped with Rhodamine.

Two-beam conical diffraction in a Kerr medium

A new conical diffraction phenomenon was observed when two beams of the same or different frequencies intersect as they pass through a CS2 cell. Light is emitted on the surface of a circular cone that is centered in each one of the two beams and has an angular extent equal to twice the crossing angle between the incident beams. The origin of this effect is discussed and a quantitative study of the conical emission intensity is given.

Observation of spatial cross-phase-modulation in DMSO

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.

Interference effects in multi-wave mixing and their control by phase-modulation of the laser beams

We developed a new technique which allows measurements of the relative amplitudes of the third- and fifth-order susceptibilities, as well as their relative phases. Preliminary results for a semiconductor doped glass that illustrate the theoretical predictions are presented.