Millijoule pulse energy second harmonic generation with single-stage photonic bandgap rod fiber laser

In this paper, we demonstrate, for the first time, a single-stage Q-switched single-mode (SM) ytterbium-doped rod fiber laser delivering record breaking pulse energies at visible and UV light. We use a photonic bandgap rod fiber with a mode field diameter of 59μm based on a new distributed-mode-filtering (DMF) fiber design, where germanium-doped high-index inclusions are added in order to enable efficient suppression of higher order modes. The rod fiber design is illustrated.