Weizhe Chen

Optical limiting properties of metal nanowires

Metal (Cu, Co, Ni, Pd, Pt, and Ag) nanowires (MNWs) have been produced using anodic aluminum oxide as template. The grown MNWs are characterized by scanning electron microscopy, x-ray diffraction, transmission electron microscopy, and electron diffraction. The optical limiting properties of the MNWs are also studied and results obtained at 532 and 1064nm indicate that MNWs have broadband optical limiting capability and the optical limiting performances of some MNWs are comparable to or better than that of carbon nanotubes. It was found that the nonlinear response of MNWs is dominated by nonlinear scattering.

Gravitation-dependent, thermally-induced self-diffraction in carbon nanotube solutions

We report the observation of thermally-induced self-diffraction in carbon nanotube (CNT) solutions under the influence of the gravity. We present a theoretical model in which CNTs are assumed to obey the Boltzmman distribution law. Under the approximations of small temperature rise and a very narrow distribution of CNT masses, the model simulation is consistent with the data measured at low laser powers. An immediate application of such a gravitation-dependent characteristic is the optical measurement for molecular weights of CNTs.

Optical limiting phenomena of carbon nanoparticles prepared by laser ablation in liquids

We report optical limiting properties of carbon nanoparticles, which were made in liquids by laser ablation of a bulk carbon target. The carbon nanoparticles were analyzed with micro-Raman spectroscopy, UV-Vis spectroscopy and Electron microscopy. Optical limiting responses towards 532-nm wavelength were measured with a 7-ns Nd:YAG laser. Nanoparticle size and laser pulse repetition rate effects on optical limiting behaviour were studied. A model was proposed to explain the physical origin of this nonlinear optical process. This work can provide useful information for designing carbon nanoparticle based optical limiters.

OPTICAL LIMITING STUDIES OF NEW CARBON NANOCOMPOSITES AND AMORPHOUS SixNy OR AMORPHOUS SiC COATED MULTI-WALLED CARBON NANOTUBES

By using fluence-dependent transmission measurement with nanosecond laser pulses, we have studied optical limiting (OL) properties of new carbon nanocomposites as well as amorphous SixNy or amorphous SiC coated carbon nanotubes suspended in distilled water. The observed nonlinearity at 532 nm contributed to OL performance of the carbon nanocomposites or carbon nanoballs (CNBs) is suggested to have its origin in the optically induced heating or scattering effects. It is found that when the linear transmittance of the CNBs is less than or equal to 70%, the intensity-dependent transmission of the CNBs is comparable to that of C60. While at 80% linear transmittance, CNBs possess better OL behavior than that of C60. These findings strongly support a potential application of CNBs for all laser protection devices. We have also observed OL effects in the amorphous silicon nitride (a-SixNy) and amorphous silicon carbide (a-SiC) coated multi-walled carbon nanotubes (MWNTs) at wavelengths of 532 and 1064 nm, and found that their OL performances are slightly poorer than that of their parent MWNTs. The possible sources of thickness-dependent OL effects of a-SixNy and a-SiC coated MWNTs are discussed.

Solvent effect and wavelength effect of laser-synthesized carbon nanoparticle colloids on optical limiting

We report the optical limiting response of carbon nanoparticle colloids in different organic solvents. The carbon nanoparticles were prepared by Nd:YAG laser ablation of carbon target immersed in ethanol. Optical limiting properties towards 532 and 1064 nm wavelengths were measured with a 7-ns pulsed Nd:YAG laser. Strong optical limiting effect was detected for the carbon nanoparticle colloids within a solvent having low thermal conductivity. The limiting effect at 532 nm is stronger than that at 1064 nm. Possible mechanisms of optical limiting were discussed.