Abstract
In this paper, we describe a thermally guided fiber-rod amplifier and laser oscillator, which exploit thermal guiding to achieve mode control. This power scalable approach operates with mode sizes that are typically an order of magnitude larger than traditional single-mode fibers. Operating as an amplifier, we achieve a small-signal gain of 5 dB at 1030 nm whilst maintaining excellent beam quality (M2 < 1.1). In a laser configuration, we obtained 13.1 W of diffraction-limited (M2 < 1.1) output power at 1032.5 nm, with a slope efficiency 53% with respect to absorbed power. A model predicting beam evolution through the thermally guided fiber-rod gain medium is presented and validated.
Highlights
Lasers with high average power, high peak power, large pulse energy, excellent beam quality, and high efficiency are sought after for numerous applications including materials processing, defence, and scientific research
The resonator design dictates the size of the free-space laser mode, whilst in a fiber, the guided mode is defined by the engineered refractive index profile
Excellent beam quality was achieved at maximum output power with M2 < 1.1
Summary
Lasers with high average power, high peak power, large pulse energy, excellent beam quality, and high efficiency are sought after for numerous applications including materials processing, defence, and scientific research. The use of thermal guiding as the guidance mechanism in Yb-doped index-antiguiding-core fibers has been reported in [8], and numerical studies on single-mode operation of a thermally guided large-mode-area fiber amplifier are reported in [9] In this contribution, we investigate a ‘fiber-rod’ geometry with a much larger Yb-doped core and a much shorter device length. We investigate a ‘fiber-rod’ geometry with a much larger Yb-doped core and a much shorter device length This approach which we refer to as a thermally guided fiber-rod (TGFR) laser occupies the domain between bulk rod and traditional fiber lasers. The TGFR laser is a power scalable concept, which aims to achieve high average and/or peak power, large pulse energy, and excellent beam quality by combining the advantages of rod and fiber lasers whilst avoiding their limitations. The prospects for further power scaling whilst maintaining diffraction-limited single-mode beam quality are considered
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