Real-time fine-tuning ultrafast supercontinuum generation and pulse compression in hybrid nonlinear multipass cavity

Self-compressible multipass cavities (MPCs) operating in the near-infrared typically rely on mirrors with anomalous dispersion to counterbalance the normal dispersion introduced by the nonlinear medium. However, the use of such fixed dispersion-compensating elements limits the flexibility and scalability of the system. To overcome this, we propose a hybrid design in which a bulk nonlinear plate providing weak anomalous dispersion is embedded within a tunable gas-filled cavity that contributes normal dispersion. This configuration enables dynamic dispersion control via gas pressure and spatial parameters. Using carrier-resolved 2D+1 pulse propagation simulations, we evaluate the feasibility of achieving strong spectral broadening and temporal compression in such a setup. The results show that the interplay of recurrent self-focusing, spatio-temporal energy redistribution, self-phase modulation and partial frequency rephasing enables broadband spectral generation and pulse compression without the need for chirped mirrors. By optimizing the net group-velocity dispersion slightly towards the anomalous side, isolated sub-pulses as short as 4.6 fs are obtained with an energy efficiency exceeding 40%. This corresponds to spectral broadening and temporal compression factors of 14 and 21, respectively. This method offers a cost-effective, flexible, and experimentally viable alternative, with performance comparable to traditional self-compression MPCs based on dispersive mirrors in the near-IR regime. Self-compressible multipass cavities for near-infrared few-cycle pulse generation rely on fixed-dispersion mirrors, which limits scalability and tunability. The authors propose to embed a bulk nonlinear plate providing weak anomalous dispersion within a tunable gas-filled cavity contributing normal dispersion, enabling dynamic and fine control of the net dispersion toward the anomalous regime and efficient broadband generation via nonlinear spatio-temporal effects.