Laser Cooling 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 a ytterbium-doped 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 (LITMoS) 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 highlight that practical radiation-balanced designs are more demanding on the fiber material properties, especially on the background absorption, than are solid-state laser cooling experiments.