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Enhancement Of Third‐Order Nonlinear Optical Susceptibilities In Single‐Walled Carbon Nanotubes

We have measured third‐order nonlinear susceptibility (χ(3)) of semiconducting and metallic single‐walled carbon nanotubes (SWNTs) by a Z‐scan method. The imaginary part of χ(3) value for fundamental absorption band in semiconducting SWNTs is one order of magnitude or more larger than those for second transition in semiconducting tube and the transition for metallic SWNT. The χ(3) value increases with increasing tube diameter. These results can be explained by the enhancement of nonlinearity by exciton effects.