C. A. C. Bosco

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.

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.

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.

Substrate dependent ultrafast dynamics in thin NiFe films

We have studied the ultrafast electronic response of thin NiFe films by femtosecond transient reflectivity measurements. The experiments were performed on films with varying thicknesses, substrates, and pump fluences. It has been observed that for high excitation densities the electron cooling time depends strongly on the nature of the underlying substrate and we attribute our results to transport of hot carriers out of the excited region. In particular, we have observed that for NiFe over NiO, carrier transport should be less important than for NiFe over Si.

Near-infrared nonlinear properties of a glass–ceramic containing sodium niobate nanocrystals

We have investigated the third-order nonlinear optical response of a niobic–silicate glass–ceramic containing sodium niobate (NaNbO3) nanocrystals using picosecond Z-scan and femtosecond optical Kerr gate techniques at 1064 and 800 nm, respectively. The results show a large dependence of the nonlinear refractive index (n2) on the volume fraction occupied by NaNbO3 crystallites. Nonlinear absorption is negligible for all samples and the response time of the nonlinearity was shorter than 100 fs demonstrating that this material is a promising candidate for ultrafast optical switching.

Nonlinear refractive behavior of a transparent glass-ceramic containing NaNbO/sub 3/ nanocrystals in the infrared

The nonlinear optical behavior of a glass-ceramic containing sodium niobate (NaNbO/sub 3/) nanocrystals (GC-SNN) was studied in recent experiments where the third-order susceptibility, /spl chi//sup (3)/, at 532 nm was measured using nanosecond power limiting and picosecond Z-scan techniques. It was shown that the presence of NaNbO/sub 3/ nanocrystals influences the magnitude of the nonlinear (two-photon) absorption coefficient (/spl alpha//sub 2/) and the nonlinear refractive index (n/sub 2/) of the material. Here we extended our previous studies probing /spl chi//sup (3)/ at wavelengths where nonlinear absorption contributions are negligible.