Gigantic optical stark effect and ultrafast relaxation of excitons in single-walled carbon nanotubes

We report a splitting and a shift of exciton absorptions in semiconducting single-walled carbon nanotubes (SWNTs) by resonant and off-resonant excitation using a fs laser pulse, respectively. This is the first unambiguous observation of the optical Stark effect of excitons in SWNTs, which is responsible for their high optical-switching performance. By scrutinizing transient absorption spectra from the mid-to near-infrared region (0.1-0.8 eV), the ultrafast recovery of real carrier excitations characteristic of bundled structures was attributed to the energy- and charge-transfer processes to metallic SWNTs.