L. H. Acioli

Infrared‐to‐visible CW frequency upconversion in Er3+‐doped fluoroindate glasses

We report on efficient frequency upconversion in Er3+‐doped fluoroindate glasses. The process is observed under 1.48 μm laser diode excitation and results in the generation of strong blue (∼407 nm), green (∼550 nm), and red (∼670 nm) radiation. The main mechanism that allows for upconversion appears to be the energy transfer among Er3+ ions in excited states. The results illustrate the large potential of this new class of glasses for photonic applications.

Measurement of high‐order optical nonlinear susceptibilities in semiconductor‐doped glasses

The optical susceptibilities of CdSxSe1−x ‐doped glasses were observed up to χ(11) using a spatially resolved phase‐matched multiwave mixing technique. Using a pulsed dye laser tuned near the band gap, measurements were performed for ‖χ(3)‖, ‖χ(5)‖, and ‖χ(7)‖ in four different commercial filter glasses.

Ultrafast chi /sup (3)/-related processes in semiconductor doped glasses

Experimental results are described for exploiting the fast and large nonlinear susceptibility of semiconductor-doped glasses (SDGs). Self-diffraction experiments were performed using incoherent broadband lasers with femtosecond time resolution yielding new information on the time response of the SDG nonlinearity. The use of backward nondegenerate wave-mixing to demonstrate yellow-to-green frequency conversion with femtosecond resolution is reported. In addition, results are presented which demonstrate the use of the SDG as a picosecond all optical gate at a 100-MHz repetition rate. >

Temporal coherent control of a sequential transition in rubidium atoms.

An experimental investigation of the coherent interaction of femtosecond pulses with two resonant sequential transitions of Rb atoms is presented. Fluorescence from the atomic system exhibits beating at a frequency given by difference in the sequential atomic transitions. The results are interpreted in terms of quantum interference in the induced coherence and its interaction with the field that results from a cooperative emission process.

Ultrafast nonlinearity of antimony polyphosphate glasses

We report on the ultrafast nonlinearity of antimony polyphosphate glasses measured using the Kerr shutter technique. The nonlinear refractive index, n2, was (1.1±0.2)×10−14 cm2/W at 800 nm, and enhancement of n2 by ≈80% was observed by adding 10% of lead oxide in the glass composition. The full width at half-maximum of the third-order correlation signal was 150 fs, which implies a fast response of the samples (⩽100 fs). Nonlinear absorption was negligible in the range of intensities used.

Femtosecond dynamics of semiconductor‐doped glasses using a new source of incoherent light

The characterization and application of a new source of incoherent light for studies of ultrafast processes in condensed matter is described. It is based on the stimulated Raman effect in monomode optical fibers and has a coherence time of ∼80 fs. As an application, we have measured the homogeneous dephasing time of CdSxSe1−x‐doped glasses and obtained a value of 14±4 fs for above‐gap excitation at room temperature.

Antimony orthophosphate glasses with large nonlinear refractive indices, low two-photon absorption coefficients, and ultrafast response

Antimony glasses based on the composition Sb2O3–SbPO4 were prepared and characterized. The samples present high refractive index, good transmission from 380to2000nm, and high thermal stability. The nonlinear refractive index, n2, of the samples was studied using the optical Kerr shutter technique at 800nm. The third-order correlation signals between pump and probe pulses indicate ultrafast response (<100fs) for all compositions. Enhancement of n2 was observed by adding lead oxide to the Sb2O3–SbPO4 composition. Large values of n2≈10−14cm2∕W and negligible two-photon absorption coefficients (smaller than 0.01cm∕GW) were determined for all samples. The glass compositions studied present appropriate figure-of-merit for all-optical switching applications.

Coherent accumulation in two-level atoms excited by a train of ultrashort pulses

In this paper we consider the interaction of inhomogeneously broadened two-level atoms with a train of pulses from a femtosecond mode-locked laser. Analytical results are obtained for the case in which the atomic relaxation times are longer then the laser repetition period, leading to accumulation in both population and coherence. These results are adequate for arbitrary pulse areas, and saturation effects are discussed. We illustrate our analytical results with a comparison to a direct numerical integration of the Bloch equations.

Nonlinear optical properties of tungstate fluorophosphate glasses

The optical nonlinearity of tungstate fluorophosphate glasses, synthesized in the NaPO3-BaF2-WO3 system, was investigated through experiments based on the third-order susceptibility, χ(3). Nonlinear (NL) refraction and NL absorption measurements in the picosecond regime were performed using the Z-scan technique at 532 nm. NL refractive index, n2∝Re χ(3), ranging from 0.4×10−14 cm2/W to 0.6×10−14 cm2/W were determined. The two-photon absorption coefficient, α2∝Im χ(3), for excitation at 532 nm, vary from 0.3 to 0.5 cm/GW. Light induced birefringence experiments performed in the femtosecond regime indicate that the response time of the nonlinearity at 800 nm is faster than 100 fs. The experiments show that χ(3) is enhanced when the WO3 concentration increases and this behavior is attributed to the hyperpolarizabilities associated to W–O bonds.

Negative nonlinear absorption in Er3+-doped fluoroindate glass

We report the observation of negative nonlinear absorption in fluoroindate glasses doped with erbium ions. The pumping wavelength is 800 nm which is doubly resonant with Er3+ ions transitions. A large nonlinear intensity dependence of the optical transmittance and strong upconverted fluorescence are obtained. The dependence of the upconverted fluorescence intensity with the laser power is described by a system of coupled-rate equations for the energy levels’ populations.