Mode-locking fibre lasers with the E22 transition of carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) are being widely investigated as saturable absorbers for initiating and maintaining mode-locking. All mode-locked fibre laser systems based on SWCNT saturable absorbers, demonstrated to date, have used the first electronic transition of the nanotubes, known as E₁₁, which corresponds to the single real gap in the electron density of states (DOS) of semiconducting nanotubes . This paper clearly demonstrates saturable absorption on the E₂₂ transition by using it to mode-lock ytterbium doped fibre ring laser for the first time. This discovery should enable the use of SWCNT saturable absorbers at much shorter wavelengths, into the visible spectral region. A transparent carboxymetylcellulose film with homogeneously dispersed individual SWCNTs was used as the saturable absorber.