Experimental investigation of delivery and spectral broadening of nanosecond laser pulses in Bragg fiber with silica core

Different types of optical fibers have been studied for delivery of high optical powers. Silica and plastic fibers are used for the VIS and NIR spectral ranges, while sapphire, hollow-core, Bragg, or photonic crystal fibers can be used also in the mid-IR range. Bragg fibers with silica cores and large fundamental-mode area could be an attractive solution for the high laser power delivery at 1064 nm. In this paper we present results of the experimental investigation of nanosecond laser pulse propagation through a laboratory-fabricated Bragg fiber with a silica core similar to fiber used in but with higher refractive index contrast. Our Bragg fiber consists of a silica core with the diameter of ~30 μm surrounded by three circular bilayers composed of one layer with a high and one layer with a low refractive index with a contrast up to 0.035. For the high power delivery experiments a laboratory-designed passively Q-switched quasi-continuously pumped Nd:YAG laser in a bounce geometry was used as a radiation source. The single pulses with the duration of 9 ns and the energy up to 1 mJ at 1.06 μm in nearly fundamental transversal mode were coupled into the fiber using a single lens L1. The experimental setup is shown in Fig. 1.