Damage mitigation in the Kagome hollow core fiber used for the delivery of short high-energy pulses

This article is focused on the design of a beam delivery system based on hollow-core photonic crystal fiber. For our experiment, we chose a fiber with the Kagome structure developed by GLOphotonics. The central wavelength of the delivered beam was 1030 nm, so we chose the fiber PMC-C-Yb-7C. The first part of the article is a brief introduction to PERLA 100, the laser used for testing the efficiency of the beam delivery system developed by HiLASE Centre. The reader will be acquainted with the laser system parameters. The input beam parameters play an important role in the efficiency of focusing into the fiber. One of the key parameters is the M2 of the beam, as it has a direct effect on the size of the waist at the point of entry into the fiber. Another important parameter is the maximum energy in one pulse which can destroy the fiber structure. The size of the focusing point must match the size of the MFD of the fiber. Therefore, it is necessary to precisely define the size of the input beam into the focusing assembly with an accuracy of micrometers and to get rid of as many degrees of freedom as possible in the actual setup of the entire system. Another critical parameter is the size of the fiber input angle. The article aims to eliminate as many critical points as possible when setting up a focusing system and thus prevent damage to the fiber structure. One of the points is the simulation and calculation of the maximum possible loading of the fiber microstructure before its damage. With the help of gradual design modification, the aim is to achieve a coupling efficiency of more than 90 % by scaling the PERLA 100 output power from units of W up to 100 W.