We present a simple method to measure the topological charges of optical vortices with multiple singularities. Using a cylindrical lens, a vortex beam can decay into a light field distribution with multiple separated dark holes, whose number just equals the topological charge of the input beam. This conclusion is then verified via experiments and numerical simulations of the propagation of vortex beams with multiple singularities. This method is also reliable to measure the topological charges of broadband vortex beams with different distributions of singularities, which does not resort to multiple beam interferometric experiments.
In this study, we presented a high-power widely tunable all-fiber narrowband superfluorescent fiber source (SFS) by employing two tunable bandpass filters and three amplifier stages. More than 935 W output power is achieved, with a slope efficiency of >75% and a beam quality factor of M2=1.40. The tuning of the narrowband SFS ranges from ∼1045 nm to ∼1085 nm with a full width at half maximum linewidth of less than 0.71 nm. The tunable narrowband SFS stably operates without the influence of parasitic oscillation and self-pulsing effects under maximum power. To the best of our knowledge, this study is the first to demonstrate a widely tunable all-fiber narrowband SFS around 1 µm wavelength region with output power reaching kilowatt-level.
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