Simplified, athermal fiber designs for high power laser applications

Thermo-optical effects are known as big challenges for power scaling of fiber lasers and amplifiers. Several effects that significantly reduce the laser performance, such as thermal lensing or the onset of transverse mode instability (TMI), are based on thermo-optical effects. Thermal lensing leads to a change of the fiber guiding properties and results in mode-shrinking, reducing the threshold of nonlinear effects. TMI arises from a thermally induced index grating due to mode interference and results in fluctuations of the output beam profile [1]. This effect becomes more pronounced with increased core diameters due to reduced guiding strength and increased thermal load.