Fiber and bulk lasers form two distinct classes of solid-state laser, both of which have achieved tremendous success in various arenas, but they are not without their limitations. In this paper, we investigate an alternative laser geometry occupying a domain that lies between traditional fiber and bulk laser systems. This geometry comprises a fiber-based thin-rod structure, with a diameter on the order of several hundred microns, and with length on the order of several centimetres. The motivation is to combine the advantages of the fiber geometry for excellent thermal management and the bulk geometry for greater immunity to non-linear effects and optical damage, whilst elegantly controlling the laser mode profile using thermally-induced waveguiding.
Rare earth ion-doped silica is an excellent candidate to demonstrate the thermally-guided fiber-rod laser (TGFRL) due to its high fracture limit, positive thermo-optic coefficient and well-established fabrication which can produce high purity material with exceptionally low loss. A 300μm core diameter, triple-clad Yb-doped fiber is used to demonstrate the TGFRL. Thermally-induced waveguides can be tailored to have significantly larger transverse dimensions than conventional ‘engineered’ waveguides yielding potential performance benefits, especially in pulsed mode.
We will present results covering thermally-induced waveguiding, amplification performance and cw laser performance at 976nm and 1030nm, with >10W achieved at 1030nm with excellent beam quality, M2 < 1.1, and slope efficiencies approaching 50% with respect to absorbed pump power. We will also present preliminary results for amplification of radially-polarised beams, highlighting the potential of these devices in a range of applications.
Callum R. Smith, Thomas Jefferson-Brain, Nikita Simakov, Alexander V. Hemming, and W. Andrew Clarkson, "Thermally guided ytterbium-doped fiber-rod laser (Conference Presentation)," Proc. SPIE 10511, Solid State Lasers XXVII: Technology and Devices, 105111I (Presented at SPIE LASE: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2288686.5751372888001.
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