Third-order optical nonlinearity of semiconductor carbon nanotubes: third harmonic generation

摘要

Within the framework of a two-band model of the electronic structure of semiconductor carbon nanotubes (CNs) we have studied the third-order nonlinear optical susceptibility x{sub}(THG){sup}(3)(ω) responsible for the effect of the third harmonicgeneration. We have obtained a theoretical expression for x{sub}(THG){sup}(3)(ω) which takes into account the contributions to the susceptibility due to purely interband transitions ofπ-electrons and combined intraband-interband motion of the latter. Adetailed analysis of the dispersion dependence of x{sub}(THG){sup}(3)(ω) has been carried out in a wide range of frequencies involving those which are much smaller than the bandgap energy and those equal to it by the order of magnitude. Thenonlinear-optical spectra of x{sub}(THG){sup}(3)(ω) are calculated numerically for nonchiral single-shell nanotubes with different radii. The results show that at the expense of the increase of the radius of the nanotubes one can achieve a giantenhancement of the power of radiation generated at the third harmonic frequency in the three-photon resonance regime. It is also shown that the magnitude of the resonant optical susceptibility of CNs can exceed the resonance values of x{sub}(THG){sup}(3)for the fullerenes C{sub}60 and C{sub}70 by several orders. The results obtained allow us to give a positive prognostic estimate of CNs as a new class of materials for nonlinear optics.