Anisotropic saturable absorption of single wall carbon nanotubes aligned in polyvinyl alcohol

ABSTRACTWe report anisotropic optical absorption and saturable absorption (SA) properties of aligned single wall carbon nanotubes (SWNT) embedded in the mechanically stretched polyvinyl alcohol (PVA) film. Polarized absorption spectra of the film showed a strong anisotropy for the near-infrared band gap transition of semiconductor SWNT with a dichroic ratio of 7.4, indicating the good alignment of the embedded SWNT. The SA property of the band gap transition measured using a polarized femtosecond fiber laser showed a strong polarization angle dependence for the stretched film. When the polarization of light is parallel to the stretching direction, the absorption saturation of the stretched film became more efficient than that of the unstretched film because of the apparently stronger transition moment.