Graphene-multilayer-saturable-absorber-based passively mode-locked Ho-doped fiber front-end for seeding of a 1-J/1-kW Ho:YAG cryogenically cooled thin-disk laser system (Conference Presentation)

Hi-tech industrial or biotechnological laser applications request for picosecond pulsed 2-um laser generating sub-1-J pulses in >kHz repetition range. At Hilase development of laser system with target to generate 1-J picosecond pulses with 1-kHz repetition rate has started. Design of the system based on Ho:YAG thin-disk generating at 2.1-um is divided into several phases. First phase includes demonstration of new mode-locked graphen-based saturable absorber Ho-doped fiber laser concept followed by preamplifier systems delivering 10-uJ pulses. Pulses are then amplified to >10-mJ level in Ho:YAG thin-disk regenerative amplifier operating at 10-kHz, and finally amplified in double stage cryogenically-cooled multi-pass amplifier to 1-J at 1-kHz so average output power reaches 1-kW in mid-IR. We present a concept of this laser system with emphasize on the front-end and the first regen. The holmium fiber front-end is pumped by a continuous wave 0.5-W thulium fiber laser generating at wavelength of 1950-nm. Mode-locking in the oscillator is reached by graphene multilayer optical element as a passive saturable absorber (GSA). The GSA provides broadband wavelength operation and is promising for MIR sources. In the laser setup, the GSA is placed in a free-space cavity as a part of ring laser configuration. This oscillator produces <10-ps-pulses with ~nJ energy and <40-MHz repetition rate. The repetition rate reduces acousto-optic modulator, pulses are pre-amplified in a chain containing Ho-doped fibers and a single crystal fiber to 10-uJ/10-to-100-kHz, and seeded to thin-disk regen. We expect demonstration of the front-end, detailed design of first regenerative amplifier and conceptual design of full system.