Ultrashort laser pulse spatiotemporal profile manipulation using a single-mode-few-mode optical fiber device

Abstract

Ultrashort laser pulse propagation through few-mode optical fibers is a complex spatiotemporal event: due to mode spatial structures and intermodal delays and dispersions, pulses in such fibers experience spatial patterns and temporal elongations, which are generally considered detrimental for beam quality and pulse shape. However, with careful control of the launched modal contents and their interactions, we demonstrate that, using a single-mode-few-mode (SFe) optical fiber device, ultrashort pulses with various desirable spatiotemporal properties can be achieved. In the SFe device, pulse transformations over space, time, and frequency are related by multimode interference, and in the far field, pulse profile can be obtained by calculating diffraction integrals. We show that, using two example cases (a Bessel-like pulse and an optical bottle pulse), our approach can generate spatiotemporally structured pulses potentially suitable for applications in material science and biological imaging.