Boosting the Nonlinear Optical Response of Carbon Nanotube Saturable Absorbers for Broadband Mode-Locking of Bulk Lasers

Single-walled carbon-nanotube absorbers are experimentally demonstrated for laser mode-locking. A saturable absorber device is used to mode-lock three different bulk solid-state lasers in a 500 nm-wide wavelength interval. The devices exhibit a low saturation fluence of <10 mu J cm(-2), low scattering losses, and an exceptionally rapid relaxation, with time constants reaching <100 fs. The latter two properties are explained by a decreased curling tendency and increased tube-to-tube interactions of the nanotubes, respectively. These properties are the result of an optimized manufacturing procedure in combination with the use of a starting material with a higher microscopic order. The decreased scattering enables universal use of these devices in bulk solid-state lasers, which tend to be highly sensitive against non-saturable device losses as caused by scattering. The favorable saturable absorption properties are experimentally verified by mode-locking the three lasers, which all exhibit near transform-limited performance with about 100 fs pulse duration. The complete and unconditional absence of Q-switching side bands verifies the small saturation fluence of these devices.