Yb:KLuW channel waveguide lasers passively Q-switched by evanescent-field interaction with carbon nanotubes

Highly efficient and compact pulsed laser sources have tremendous potential for integrated photonic devices in numerous applications including spectroscopy, metrology and microscopy. Yb³⁺-doped monoclinic double-tungstate crystals exhibit broad and large absorption and emission cross-sections and extremely low quantum defects. Channel waveguide structures have been actively studied for miniaturization of laser systems and efficient fundamental-mode laser operation with low lasing thresholds. One of the powerful methods to fabricate waveguide structures in a transparent material is the femtosecond direct laser writing (fs-DLW). Recently, pulsed waveguide lasers utilizing saturable absorbers (SAs) have been demonstrated with SESAM and low-dimensional carbon nanostructures. [1-3] Intrinsic characteristics such as ultrafast response, broadband nonlinear absorption and flexibility for integration make single-walled carbon nanotubes (SWCNTs) and graphene unique for various types of pulsed lasers. Placing a SA between the waveguide and the laser mirror results in additional intracavity losses and Q-switching instabilities due to thermal loads through direct-field interaction with the SA. Therefore, the damage-free coupling and the potential of a monolithic design including SAs in compact lasers are highly desired.