Continuously wavelength-tunable blueshifting soliton generated in gas-filled photonic crystal fibers.We experimentally report the generation of wavelength-tunable blueshifting soliton in the visible spectral region through a gas-filled single-ring photonic crystal fiber (SR-PCF).  In particular, in a He-filled SR-PCF, we observed a sharp narrow-band spectral peak at the first resonant spectral region of the SR-PCF, which results from phase-matched nonlinear processes.  In addition, when Ar gas was filled into the SR-PCF, some interference fringes on the blueshifting soliton were observed at high pulse-energy levels due to plasma-induced pulse fission. 
SR-PCF
In particular, in a He-filled SR-PCF, we observed a sharp narrow-band spectral peak at the first resonant spectral region of the SR-PCF, which results from phase-matched nonlinear processes. 
He-filled SR-PCF
In addition, when Ar gas was filled into the SR-PCF, some interference fringes on the blueshifting soliton were observed at high pulse-energy levels due to plasma-induced pulse fission. 
Ar gas
These two experimental observations are confirmed by numerical simulations. 
numerical simulations