Multimode Amplification and Single-Mode Transformation Enabled by Thermal Modulation

Abstract

Boosting extraction efficiency through multimode amplification while simultaneously generating a fundamental-mode output represents the ideal paradigm for laser systems. This methodology is particularly advantageous in ultrafast lasers, where increasing output intensity is crucial. Here it is found that the thermo-optic effect, typically considered detrimental to laser performance, can instead promote mode transformation, enabling single-mode output from a multimode amplifier. Specifically, through thermal modulation, a 39% increase in output power, reaching 50 W of fundamental-mode output and a pulse width of 168 fs, in a multimode regenerative amplifier based on a Yb:CaAlGdO₄ medium—establishing a new power benchmark for this system is achieved. In addition, to validate the general applicability, the technique to a Yb:YAG gain medium, achieving a 43% power enhancement and demonstrating effective single-mode transformation is extended. The demonstrated approach can be generalized to a broad range of laser gain media for power enhancement without additional optical components or design complexities.