Amplification of high-purity scalar orbital angular momentum states in single-crystal fibers

Structured light fields with high degrees of freedom, particularly those with orbital angular momentum (OAM) states associated with the rotation of the phase front, give rise to a range of novel physical phenomena in light–matter interactions. However, direct generation of scalar OAM states at source faces limitations in power scaling, and their amplification remains an open challenge due to limited gain and mode purity. In this work, we present a straightforward approach to directly amplify scalar optical vortices by employing a two-stage single-crystal fiber (SCF) amplifier system, delivering 104.8 W laser with the OAM state of ℏ and 90.3 W of −8ℏ state. Both of the OAM states exhibit a high modal purity of >90%, indicating that such a multi-stage SCF amplifier system is particularly well-suited for direct amplification of scalar OAM light with different states. The strategy presented here paves the way for power scaling of structured light, and the generated high-power and high modal purity OAM laser beams are expected to reveal complex physical phenomena in light–matter interactions.