Ultrabroadband ring oscillator for sub-10-fs pulse generation

Abstract
A four-mirror ring cavity formed by chirped dielectric mirrors is proposed for self-mode-locked solid-state lasers. It offers, for the first time to our knowledge, the potential for approaching the gain-bandwidth limit in Ti:sapphire and related broadband lasers. Using this concept, we produced nearly bandwidth-limited 7.5-fs pulses from a feedback-initiated, self-mode-locked Ti:sapphire ring oscillator. Our experiments provide new insight into the physics and limitations of sub-10–fs oscillators.