Average-power scalability of multi-cycle terahertz sources based on periodically poled lithium niobate stacks.

We demonstrate that narrowband multi-cycle terahertz (MC-THz) sources based on periodically poled lithium niobate (PPLN) wafer stacks can be driven by high repetition rate, high energy sub-picosecond ytterbium-doped lasers. Operating at a 10-kHz repetition rate with up to 104 W of pump power on a 10-wafer stack, we measure 26.4 mW of THz average power for a narrowband multi-cycle source. We identify and quantify strong lensing effects causing dramatic beam focusing in 47 wafer stacks, which act as a primary limitation in the current configuration, and present mitigation strategies for future scaling.