Mode-locking of a femtosecond-laser-inscribed Yb:YAG channel waveguide laser using a carbon nanotube saturable absorber

Abstract

Compact pulsed laser sources are of interest for diverse application areas. Due to their broad gain bandwidth, high Stokes efficiency and low thermal load near the 1 μm spectral region, ytterbium doped laser materials are promising for such devices. Channel waveguides in such gain media provide compact laser systems and deliver efficient single-mode laser operation with low laser thresholds. One of the widely-used techniques for manufacturing channel waveguides in transparent materials including laser gain media is fs-laser inscription. Inscribing two parallel tracks inside a laser crystal with a distance of few 10 μm allows for highly efficient laser operation in few mm-long monolithic resonators [1]. Pulsed operation of fs-laser inscribed channel waveguide lasers has been demonstrated with saturable absorbers (SAs) including SESAMs and low-dimensional carbon nanostructures. Intrinsic fast response time, linear and nonlinear absorption in a broad spectral range and relatively simple fabrication processes make graphene and single-walled carbon nanotubes (SWCNTs) a cost effective approach for saturable absorbers for various laser types including channel waveguide lasers. Recently, Q-switched [2-4] and even mode-locked operation at 1.94 GHz repetition rate [5] have been demonstrated with fs-laser inscribed Yb3+-doped waveguides. However, mode locking of fs-laser inscribed waveguide lasers by employing carbon nanotubes is not yet reported.