Over the past decades, high-power fiber lasers and amplifiers have been extensively under research to achieve higher output powers. However, temperature rise in the core of the fiber lasers and amplifiers has been a hindrance to an acceptable stability and efficiency in high power operation. Radiation-Balancing is a viable technique that has been introduced for effective heat mitigation in lasers and amplifiers by S. Bowman in 1995. The Radiation Balanced Laser (RBL) technique relies on solid-state laser cooling as a self-cooling mechanism to mitigate the generated heat in the lasers and amplifiers. To implement the aforementioned idea in the fiber lasers and amplifiers, a set of issues should be scrutinized. Here in this study, we will delve into two important issues for building a radiation-balanced fiber laser or amplifier: (i) the amenability of silica glass (as the most common host material in optical fibers) to laser cooling and (ii) an efficient design for implementing radiation balancing in the fiber laser or amplifier.

For a radiation-balanced laser or amplifier, the gain medium should be amenable to laser cooling, therefore, the observation of laser cooling in silica glass is a necessary step for radiation-balancing in fiber lasers and amplifiers. In this study, to the best of our knowledge, for the first time we report the first observation of laser cooling in the silica glass. We will show a temperature drop of 0.7 K below the ambient temperature in a Yb-doped silica fiber preform. Our analyses also show that due to small doped area of (Double-Clad) DC fibers, the radiation-balancing cannot effectively mitigate the generated heat in the moderate-power operation regime (powers larger than tens of watts.); therefore, a new configuration that we name “Core/Cladding ion-doped configuration” is introduced to enable the DC fiber amplifiers to mitigate the generated heat in the moderate-power operation regime.