Delivery of nanosecond laser pulses by multimode anti-resonant hollow core fiber at 1 um wavelength

In this paper we explore the application of low-loss multimode anti-resonant hollow-core fiber (MM-AR-HCF) in the delivery of nanosecond laser pulses at 1 um wavelength. MM-AR-HCF of large core offers a rich content of low-loss higher-order modes which plays a key role in the efficient coupling and transmission of high-power laser of degraded beam quality. In the experiment, laser pulses of an average pulse energy of 21.8 mJ with 14.6 ns pulse width (corresponding a peak power of 1.49 MW) are transmitted through MM-AR-HCF of 9.8 m length without damaging. Up to 94 % coupling efficiency is achieved where the incident laser beam suffers a degraded beam quality with and of 2.18 and 1.99 respectively. Laser-induced damage threshold (LIDT) of MM-AR-HCF measures 22.6 mJ for 94 % coupling efficiency, which is 7 times higher than that for multimode silica optical fiber with a core diameter of 200 um.