Spatiotemporal flat-top beam generated from an all-fiber mode-locking laser

The flat-top beams have significant potential for applications in micromachining and biomedicine, due to their unique intensity distribution. Therefore, spatiotemporal flat-top beams, which are all flat-top in both spatial and time domains, may significantly advance its development. Here, we demonstrate the generation of a spatiotemporal flat-top beam using an all-fiber mode-locked laser. Using nonlinear optical loop mirror (NOLM) technology, stable dissipative soliton resonance (DSR) pulses with flat-top shapes in the time domain are obtained. By superimposing the two flat-top pulses (LP 01 and VBs) with the orthogonal polarization method, a pulsed spatiotemporal flat-top beam with a flat center and steep edge in both spatial and time domains can be realized. Additionally, the duration of the obtained spatiotemporal flat-top beam can be tuned from 1.8 ns to 12.6 ns, while the spatial intensity distribution remains unchanged. Our finding provides an effective way to generate spatiotemporal flat-top beams in an all-fiber mode-locking laser, which may have significant potential applications in many fields, particularly in laser micromachining.