Nonlinear optical response of multiwalled carbon-nanotube dispersions

Experimental measurements of nonlinear optical extinction of nanosecond laser pulses by a set of conjugated copolymer/multiwalled carbon-nanotube composites dispersed in solution are reported here. The polymer poly(para-phenylenevinylene-co-2,5-dioctyloxy-meta-phenylenevinylene) and multiwalled carbon-nanotube composites were varied according to nanotube mass content. The experiments were performed with an open-aperture Z scan with 6-ns Gaussian pulses at 532 nm from a frequency-doubled, Q-switched Nd:YAG laser. The nonlinear optical extinction of the incident pulses displays enhanced dissipation of the incident light for lower incident intensities relative to increasing multiwalled carbon-nanotube content. Either the multiwalled carbon nanotubes or the polymer dominates the nonlinear response of the composite depending on the relative mass of polymer to nanotube. Effective optical coefficients with a nonlinear absorption based model are calculated, and their intensity dependence is investigated. Mechanistic implications of the optical dissipation are also discussed.