Ionization-induced adiabatic soliton compression in gas-filled hollow-core photonic crystal fibers

We investigate in the experiments the ionization-induced adiabatic soliton compression process in a short length of He-filled single-ring photonic crystal fiber. We observe that the plasma-driven blueshifting solitons show little residual light near the pump wavelength in a certain pulse energy region, leading to a high-efficiency frequency upconversion process. In contrast, at high pulse energy levels, we observe that the quality of the frequency upshifting process is impaired due to the existence of a dynamical loss channel induced by the coupling of the soliton to linear modes near the pump wavelength. In addition, through adjusting the input pulse energy, the central wavelength of blueshifting solitons can be continuously tuned over 300 nm. These experimental results, confirmed by numerical simulations, not only offer a deep insight into ionization-induced soliton-plasma dynamics in gas-filled hollow-core photonic crystal fibers, but also develop highly tunable ultrafast light sources at visible wavelengths, which may have many applications in ultrafast spectroscopy.