Power scaling limits of diffraction-limited fiber amplifiers considering transverse mode instability

Area of Science:

• Laser Physics and Photonics
• Materials Science for Optical Applications
• Fiber Optics and Amplifiers

Background:

• Thermal lensing and mode instability (TMI) limit the power scaling of fiber amplifiers.
• Understanding TMI thresholds is crucial for designing high-power fiber laser systems.
• Previous models provided foundational insights but lacked empirical validation for diverse materials.

Purpose of the Study:

• To derive an empirical threshold formula for transverse mode instability (TMI).
• To analyze and compare the power-scaling performance of different fiber amplifier materials, including silica glass, YAG, and lutetia.
• To provide guidance for optimizing fiber and amplifier designs for maximum average output power.

Main Methods:

• Development of a new theoretical model for TMI.
• Derivation of an empirical TMI threshold formula from the model.
• Experimental analysis of power-scaling performance in ytterbium-doped silica glass, YAG, and lutetia fiber amplifiers using the derived formula.

Main Results:

• The derived empirical TMI threshold formula provides a quantitative tool for performance analysis.
• Single-crystalline fiber amplifiers (YAG and lutetia) demonstrate higher potential for average power scaling compared to silica glass.
• Higher thermal conductivity in single-crystalline fibers is identified as the key factor enabling superior power scaling.

Conclusions:

• The study extends previous work on TMI by providing an empirically validated threshold formula.
• Single-crystalline fibers offer a promising pathway to achieving higher average output powers in fiber amplifiers.
• The findings offer critical insights for designing next-generation, high-power fiber laser systems by considering TMI limitations.