Band gap photobleaching in isolated single-walled carbon nanotubes

Using pump-probe characterization, band gap photobleaching has been observed from semiconducting single-walled carbon nanotubes (SWNTs) isolated in aqueous suspensions in an effort to evaluate SWNTs as a near-infrared optical material. The measured photobleaching was optimized for co-polarization of pump and probe lasers in resonance with the second and first van Hove transitions, respectively. A saturation of photobleaching intensity was observed for large pump intensities greater than similar to1 kW cm(-2) and for probe intensities approaching similar to500 W cm(-2). The observed photobleaching is attributed to the relaxation of excited electron-hole pairs to the band edges, resulting in decreased absorption and increased stimulated emission.