Evaluating the beam quality of double-cladding fiber lasers in applications.
We put forward a new β<sub>FL</sub> factor, which is used exclusively in fiber lasers and is suitable to assess beam quality and choose the LP<sub>01</sub> mode as the new suitable ideal beam. We present a new simple measurement method and verify the reasonability of the β<sub>FL</sub> factor in experiment in a 20/400 μm fiber laser. Furthermore, we use the β<sub>FL</sub> factor to evaluate the beam quality of a 3-kW-level fiber laser. It can be concluded that β<sub>FL</sub> is a key factor not only for assessing the performance of the high-power fiber laser that is our main focus, but also for the simple measurement.