Ultrashort femtosecond laser pulses are proved to be useful tools to better understand the basic physical and chemical properties underlying in the ultrafast optical responses. In particular, a tunable laser source across the wide spectral range is strongly demanded for investigating ultrafast dynamics in various materials.
Recently, a research team from State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, employed a gas-filled single-ring photonic crystal fiber (SR-PCF) to generate tunable ultrashort laser pulses via soliton-plasma interactions.
The experimental set-up includes two stages: the pulse-compression stage and soliton-dynamics stage. At first, ~45-fs pulses from a commercial Ti:Sapphire laser system centered at 800 nm were compressed to ~16 fs through a l-m-length hollow-core fiber (HCF) filled with 0.2-bar Ar. In the soliton-dynamics stage, the compressed pulses were focused into a 17.2-cm-length SR-PCF filled with 1.3-bar Ar or 10-bar He.
What was amazing was that, 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. Apart from that, in a He-filled SR-PCF, a sharp narrow-band spectral peak was achieved at the first resonant spectral region of the SR-PCF, which resulted from phase-matched nonlinear processes.
To the best of our knowledge, it was the first time to investigate the influence of the core-cladding resonance on the blueshifting soliton. These two experimental observations are confirmed by numerical simulations.
Furthermore, through properly adjusting input pulse energy, researchers found that the blueshifting soliton can obtain a high conversion efficiency (～84%) and its wavelength can be tuned over hundreds of nanometers (～240 nm).
The experiment pave the way to generate broadband wavelength-tunable light sources in the visible spectral region, which may have plenty of potential applications in ultrafast pump-probe spectroscopy.
The corresponding results, entitled “Continuously wavelength-tunable blueshifting soliton generated in gas-filled photonic crystal fibers”, were published in Opt. Lett. 44(7), 1805 (2019).
This work was supported by the International S&T Cooperation Program of China (2016YFE0119300); National Natural Science Foundation of China (NSFC) (61521093, 61635012); Program of Shanghai Academic/Technology Research Leader (18XD1404200); Strategic Priority Research Program of the Chinese Academy of Sciences (CAS) (XDB1603); Major Project Science and Technology Commission of Shanghai Municipality (STCSM) (2017SHZDZX02).
Mr. Cao Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS