A Hollow-Core Fibre Beam Delivery Line Sized by Critical Power, Mode Loss and Bend Radius

This paper presents a computed design for a 5 m hollow-core anti-resonant fibre delivery line carrying millijoule femtosecond pulses from an amplifier to a processing head. The sizing follows from applying the relevant intensity, thermal, nonlinear and geometric bounds at a single stated operating point, with every number produced by a deposited computation. The headline result is a pulse peak power of 10 GW, a margin of 90 below the stated gas critical power for self-focusing, a total line loss of 0.9 dB including the bend allowance, a throughput of 0.69, and 1.38 mJ delivered from 2.00 mJ launched. The binding constraint is identified explicitly: bend-induced loss and mode coupling when the line is routed around a workstation, and contamination of the open core ends. The design is SIMULATED, NOT MEASURED: no hardware was built for this study, and all performance figures are predictions from stated assumptions, offered as a basis for a build decision and a measurement plan.