  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.
