Third-order nonlinear optical response and nonlinear photoluminescence in multiwalled carbon nanotubes

Abstract

The nonlinear optical properties of multiwalled carbon nanotubes (MWNT) was investigated using femtosecond, picosecond and nanosecond laser pulses by the Z-scan and Degenerate four wave mixing techniques. Measurements show a significant third order nonlinear response in the both visible and near-infrared wavelengths regions, with Χ(3) values as high as 10-10 esu obtained on nanosecond and picosecond excitation and somewhat diminished Χ(3) values of the order of 10-12 esu obtained on femtosecond excitation. The temporal response at both picosecond and femtosecond excitation show a significant fast component indicating that electronic processes contribute to the third order nonlinear optical response of MWNT. This electronic role is highlighted by the observation of Van Hove singularities (VHS) in the density of states of MWNT. Unexpected visible luminescence from MWNT, observed on photo excitation at 1064 nm, is believed to arise from radiative transitions between energy states in the VHS. Our results shows that the presence of VHS enable efficient optical transitions in MWNT and furthermore the enhancement of the third order nonlinear optical response.