210-W Ultrafast Thin-Disk Laser Oscillator in Air Enabled by Negative Nonlinearities from Cascaded χ (2) Processes

We use a phase-mismatched χ (2) crystal to cancel the intracavity self-phase-modulation from air. We obtain 210-W average output power, a record value for SESAM-modelocked thin-disk lasers operated in air without complex vacuum or helium purging.