Spatiotemporal Wavevector Dynamics in Transverse Mode-Locked Beams

Transverse mode-locked (TML) beams result from the fixed-phase superposition of higher-order resonator modes. Such beams have been shown to exhibit spatiotemporally varying intensity distributions [1], i.e. their intensity distributions spatially oscillate on periodic trajectories in transverse space, where the trajectories are dependent on the transverse mode composition. A superposition of Hermite-Gaussian modes, for example, would yield a line-scanning beam, whereas a superposition of Laguerre-Gaussian modes would result in a circular beam scanning trajectory [2]. TML beams have been successfully generated with various schemes in free-space solid-state lasers [1], [2], fiber lasers [3], and by conversion of longitudinally mode-locked light fields [4]. Thus far, only the intensity dynamics of these beams have been investigated, while phase dynamics have been left unexplored, although they play a critical role for potential future applications involving fiber coupling and other phase-sensitive processes.