Characterization of Yb-doped ZBLAN fiber as a platform for radiation-balanced lasers

Abstract

Recent advances in power scaling of fiber lasers are hindered by the thermal issues, which deteriorate the beam quality. Anti-Stokes fluorescence cooling has been suggested as a viable method to balance the heat generated by the quantum defect and background absorption. Such radiation-balanced configurations rely on the availability of cooling-grade rare-earth-doped gain materials. Herein, we perform a series of tests on an ytterbium-doped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:msub> <mml:mi>ZrF</mml:mi> <mml:mn>4</mml:mn> </mml:msub> <mml:mo>–</mml:mo> <mml:msub> <mml:mi>BaF</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mo>–</mml:mo> <mml:msub> <mml:mi>LaF</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:mo>–</mml:mo> <mml:msub> <mml:mi>AlF</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:mo>–</mml:mo> <mml:mi>NaF</mml:mi> </mml:mrow> </mml:math> (ZBLAN) optical fiber to extract its laser-cooling-related parameters and show that it is a viable laser-cooling medium for radiation balancing. In particular, a detailed laser-induced modulation spectrum test is performed to highlight the transition of this fiber to the cooling regime as a function of the pump laser wavelength. Numerical simulations support the feasibility of a radiation-balanced laser, but they highlight that practical radiation-balanced designs are more demanding on the fiber material properties, especially on the background absorption, than solid-state laser-cooling experiments.