Abstract
We have investigated third-order nonlinear optical properties of bundled and isolated semiconducting single-walled carbon nanotubes (SWNTs) by means of Z-scan method, pump–probe method, and two-beam time-resolved degenerate four-wave mixing (DFWM) method. The figures of merit Im χ (3)/ α in both bundled and isolated SWNTs samples were found to be enhanced with increasing tube diameter. The measured Im χ (3)/ α value in the bundled SWNTs was an order of magnitude smaller than that in the isolated SWNTs. Both population relaxation time T 1 and phase-relaxation time T 2 for bundled samples were smaller than those in the isolated samples. These experimental results can be explained by an increase in nonradiative recombination rate and phase-relaxation rate in the bundled sample. The phase-relaxation time T 2 is considered to have a significant role in the enhancement of Im χ (3)/ α.
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