Self-Phase Modulation Induced Beam Quality Degradation in Hollow-Core Fibers

The development of ultrafast lasers with high pulse energies (~mJ) and high average powers (several hundred watts to single-digit kilowatts) has enabled various applications in industrial laser material processing. These applications include the drilling of micro-holes with a high aspect ratio, high-throughput laser milling of silicon, and the structuring of stainless steel to achieve superhydrophobic surfaces with high productivity. For the flexible delivery of ultrashort laser pulses inhibited-coupling guiding hollow-core photonic crystal fibers (IC-HCPCFs) are considered as an ideal solution. Thanks to the low power overlap of the core-guided light with the surrounding glass in the range of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10^{-4}\sim 10^{-6}$</tex> [1], IC-HCPCFs can handle laser beams with high powers and intensities. Although many research groups have demonstrated the delivery of ultrashort laser pulses with high peak intensities in ambient air [2], [3], the impact of nonlinear effects, particularly self-phase modulation (SPM), on delivering such pulses with near to diffraction-limited beam quality remains unexplored.