What major limitation of older $ ext{Nd:YAG}$ rod lasers does the fiber laser inherently solve due to its geometry?

Answer

Thermal lensing

The fiber laser’s long, narrow core structure provides a high surface-area-to-volume ratio, allowing waste heat to dissipate much more effectively, thus mitigating the thermal lensing common in bulk solid-state rod lasers.

What major limitation of older $	ext{Nd:YAG}$ rod lasers does the fiber laser inherently solve due to its geometry?
inventionlaserfiber