Michael Etienne

Third-order nonlinear optical properties of a cadmiun sulfide-dendrimer nanocomposite

We have investigated the nonlinear optical response of thin films consisting of a poly(propyleneimine) dendrimer matrix having diaminobutane core with and without small 2.2nm diameter CdS quantum dots. Large nonlinear coefficients and low nonlinear absorption losses were observed at 532 and 1064nm. The high nonlinearity and low two-photon absorption yielded promising figures of merit for nonlinear optical switching applications.

Nonlinear transmission properties of nanostructures with single-wall carbon nanotubes and conductive polymers

Using the concept of self-assembly, we formed orderly structured nanocomposites based on single-wall carbon nanotubes, which were electrochemically wrapped with conductive polymers. We report on the nonlinear optical transmission characteristics of such materials.

Distributed p-n nano-interfaces

An ordered array of n-type semiconductor spheres was interfaced with a matrix of p-type material to realize a distributed structure with face-centre-cubic symmetry. Both types have been realized by the use of functionalized single walled carbon nanotubes. The structures lack typical dc junction characteristics because of connectivity between p-type regions. They exhibit nonlinear optical characteristics (ac effect), which was attributed to the quadratic Stark effect.

Pulse duration dependence of the third order optical nonlinearity of a cadmium sulfide dendrimer nanocomposite

Open and close aperture Z-scans were performed on various CdS quantum dots embedded in either generation 4 (G4) and G5 poly(propyleneimine) dendrimer films using picosecond and femtosecond pulses between 350 nm and 1 &mgr;m. The films had an average thickness of 400nm. The measured values of the third order nonlinear coefficient were among the highest off-resonance nonlinearities reported for organic and/or hybrid composites materials. However, the nonlinear response with picosecond pulses were about an order of magnitude higher than the femtosecond counterpart. We show that the nonlinear response in these materials is also a function of the dynamics of the excited states involved and that measurements of the nonlinear optical coefficient with pulses of different duration is directly correlated to the dynamics of the excited states.

Novel nonlinear distributed p-n nano-junctions made of p-doped and n-doped single-wall carbon nanotubes

We report on the nonlinear optical properties of distributed, three-dimensional, p-n nano-junctions which are based on single-wall carbon nanotubes.

Experimental and theoretical investigation of the third-order nonlinearity in CdS quantum dots in a dendrimer matrix

We have measured the nonlinear optical response of Cadmium Sulfide quantum dots (CdS QD) in a poly(propyleneimine) dendrimer matrix having diaminobutane (DAB) core. Large refractive nonlinear coefficients and low absorption losses were observed at all wavelengths. Dendrimers are nanosize, highly branched, tree like monodisperse macromolecules that emanate from a central core with a branch occurring at each monomer unit. Dendrimers encapsulations convey stability, control of emission wavelengths by QD size. The branching points in the interior of the dendrimers are occupied by tertiary nitrogen to provide numerous nucleation sites to drive formation of QD clusters of small size. The dendrimer-stabilized CdS QDs were stable at room temperature, both in solution and in solid state for several weeks. Thin films were deposited by spin casting from methanol solutions. The resulting samples consisted of a 1mm thick quartz substrate with a 200-400 Å nonlinear optical film on one side. The Z-scan technique was used to characterize the NLO response. A mode-locked YAG laser provided the laser pulses with 30-ps duration at 355 nm, 532 nm and 1064 nm at a 20-Hz repetition rate with energies per pulse ranging from few microjoules to several millijoules. These results indicate relatively large values for the nonlinear response (> 10-10 esu) at all three wavelengths. Our calculations indicate that quantum dot-organic systems have large optical nonlinearity due to interactions between excitons in the quantum dots and the organic medium. We calculate that an increase of the QD radius to ~4-8 nm will result in a substantial enhancement of the nonlinearity.