Broadband Dispersive‐Wave Emission Coupled with Two‐Stage Soliton Self‐Compression in Gas‐Filled Anti‐Resonant Hollow‐Core Fibers

The underlying mechanism of broadband dispersive‐wave emission within a resonance band of gas‐filled anti‐resonant hollow‐core fiber is studied. Both numerical and experimental results unveiled that the pump pulse with a soliton order of ≈3, launched into the hollow‐core fiber, experienced two stages of pulse compression, resulting in a multi‐peak structure of the emitted dispersive‐wave spectrum. Over the first‐stage pulse compression, a sharp increase of the pulse peak power triggers the first time of dispersive‐wave emission, and simultaneously causes the soliton frequency blue‐shift due to soliton‐plasma interactions. As the central frequency of the blue‐shifting soliton approaches to a resonance band of the hollow‐core fiber, it experiences a fast‐decreasing dispersion value in the fiber waveguide, resulting in the second stage of pulse compression. The second‐stage pulse compression triggers the second time of dispersive‐wave emission with a phase‐matched frequency slightly lower than that at the first stage. Multi‐peak spectra of the output dispersive‐waves and their formation dynamics can be understood using a delicate and unique coupling mechanism among three nonlinear effects including multi‐stage soliton compression, soliton‐plasma interaction, and phase‐matched dispersive‐wave emission. The output broadband dispersive‐wave, exhibiting good coherence and stability, can be potentially compressed to sub‐30 fs duration using a precise chirp‐compensation technique.