Kagome-type hollow-core photonic crystal fibers for beam delivery and pulse compression of high-power ultrafast lasers

Tremendous progress has been achieved in the last years in the field of ultrafast high-power sources. Among the different laser technologies driving this progress, thin-disk lasers (TDLs) have gained significant ground, both from amplifiers and modelocked oscillators. Modelocked TDLs are particularly attractive, as they allow for unprecedented high energy and average powers directly from an oscillator. The exponential progress in the performance of these sources drives growing needs for efficient means of beam delivery and pulse compression at high average power (< 100 W) and high peak power (> 10 MW). This remains a challenging regime for standard fiber solutions: microstructured large-mode-area silica photonic-crystal fibers (PCFs) are good candidates, but peak powers are limited to ≈4-6 MW by self-focusing. Hollow-core (HC) capillaries are adapted for higher peak powers, but exhibit high losses and are not suitable for compact beam delivery. In parallel to the progress achieved in the performance of ultrafast laser systems, recent progress in novel hollow-core PCF designs are currently emerging as an excellent solution for these challenges. In particular, Inhibited-coupling Kagome-type HC-PCFs are particularly promising: their intrinsic guiding properties allow for extremely high damage thresholds, low losses over wide transmission windows and ultra-low dispersion. In our most recent results, we achieve pulse compression in the hundred-watt average power regime using Kagome-type HC-PCFs. We launch 127-W, 18-μJ, 740-fs pulses from our modelocked TDL into an Ar-filled fiber (13 bar), reaching 93% transmission. The resulting spectral broadening allows us to compress the pulses to 88 fs at 112 W of average power, reaching 105 MW of peak power, at 88% compression efficiency. These results demonstrate the outstanding suitability of Kagome HC-PCFs for compression and beam delivery of state-of-the-art kilowatt-class ultrafast systems.