Determination of LMA fiber modes using beam profile measurements of a fiber laser while operating at high power

Large-mode-area (LMA) fibers can provide good beam quality even with higher-order modal content, but environmental fluctuations lead to dynamic changes in output beam characteristics. It is beneficial to measure modal content while the laser is operating at full power to assess short- and long-term laser behavior. Existing modal decomposition methods can either recover mode profiles and content of non-operating fiber or recover modal powers of an operating laser assuming known modal profiles. We present a novel method for computing both modal powers and profiles while an LMA laser operates at high power without prior knowledge of the modes.