Highly efficient DUV generation at 100 kHz via Yb pumped four-wave mixing in stretched hollow-core fibers

We report the generation of the fifth harmonic of Yb at 206 nm with pulse energies exceeding 16 $\mu$J and durations of approximately 100 fs at a repetition rate of 100 kHz. The deep ultraviolet pulses are produced using four-wave difference frequency mixing in a He-filled stretched hollow-core fiber, driven by a pump at 343 nm and seeded at 1030 nm. Guided by simulations, we carefully optimize the process, resulting in a conversion efficiency of $\sim$30% from the 343 nm pump beam.