Nonlinear Propagation of High-Energy Multimode Pulses in Solid-State Multipass Cells

Due to their controllable optical path length and flexible adjustment of optical nonlinearity, multipass cells (MPCs) have emerged as an effective platform for investigations of strong-field nonlinear optics with few-cycle pulses. Prior compression schemes frequently employed hollow core fibers. Propagation in these fibers is effectively single transverse mode, which greatly simplifies numerical modeling. Here we tackle the problem of transverse-multimode nonlinear propagation in solid-state MPCs, employing a suitably expanded unidirectional pulse propagation equation. Our numerical investigation reveals a peculiar spatiotemporal optical wave breaking mechanisms, which is intricately linked to energy transfer dynamics from the fundamental to higher-order modes. This intermodal energy reallocation results in mode-specific pulse compression, depending on the energy in each mode. Remarkably, this process induces a rapid expansion of the beam size, which leads to a mitigation of adverse thermal effects. Our study provides deeper theoretical insights into multimode nonlinear propagation in solid-state MPCs. The observed spatiotemporal phenomena as well as the observed energy transfer dynamics offer valuable guidance for the design and application of MPCs in pulse compression.