Amplification of a radially polarized beam in a thermally guiding ytterbium-doped fiber rod

Abstract

Amplification of a radially polarized beam from an Yb:YAG seed laser at 1030 nm in a very-large-core triple-clad ytterbiumdoped fiber configured as a thermally guiding fiber rod amplifier is demonstrated. The amplifier yielded a maximum output power of 10.7 W (limited by available pump power) with corresponding single-pass gain of 6.4 dB, while the radial polarization purity was maintained over the full range of pump power with a measured polarization extinction ratio of 100:1. The amplified output beam displayed the characteristic donut-shaped intensity profile with negligible beam distortion as evidenced by a measured beam propagation factor (M 2 ) of 2.1 ± 0.1. A simplified model for propagation of a radially polarized beam in a thermally guided fiber rod is developed to provide insight into the underlying design principles and to establish a strategy for scaling output power. The power scaling limitations of this approach are considered.

Radially polarized 33 W emission from a double-pass Ho:YAG thin-slab amplifier

“…For the cutting of sheet metals, radially polarized light may achieve a cutting efficiency that is up to 1.5-2 times higher than a linearly polarized or circularly polarized beam [5]. Not surprisingly, scaling the average power of radially polarized beams to meet the needs of laser cutting applications has been the subject of much interest, with recent studies investigating different amplifier architectures (such as thermally-guiding fiber rods, single-crystal fibers, face-pumped thin-disks and edge-pumped thin-slabs [6][7][8][9]) in order to increase the power from a radially polarized master-oscillator whilst preserving the beam quality and radial polarization purity.…”