Efficient and broadband Cherenkov radiations in the multi-knots of a hollow-core photonic crystal fiber cladding

The Cherenkov radiations (CRs) at visible wavelengths are efficiently generated based on the soliton self-frequency shift (SSFS) by coupling the 120 fs pulses into the fundamental mode propagated in the multi-knots of a hollow-core photonic crystal fiber cladding (HC-PCFC). When the pump operates at 830 nm with the average power of 300 mW at the knots 1-4, the central wavelengths of generated CRs λ_CR are 476 nm, 454 nm, 554 nm, and 580 nm, the conversion efficiencies η_CR are 33%, 35%, 30%, and 29%, and the corresponding bandwidths B_CR are 57 nm, 74 nm, 25 nm, and 50 nm, respectively. To the best of our knowledge, η_CR of 35% and B_CR of 74 nm are the best experimental results reported with >100 fs pump pulse. The efficient and broadband CRs can be wavelength-tunable over the whole visible wavelength by adjusting the wavelengths of pump pulses coupled into different knots. The result can be used as the multi-channel ultrashort pulse source for many important applications in the multiphoton microscope and ultrafast photonics.