Enhanced violet Cherenkov radiation generation in GeO2-doped photonic crystal fiber

We demonstrate the generation of highly efficient Cherenkov radiation (CR) in the fundamental mode of a GeO2-doped two zero dispersion wavelengths photonic crystal fiber (PCF). Using a high power femtosecond Yb-doped PCF laser emitting 100 fs pulses as the pump source, CR with an efficiency of > 40 % and a bandwidth of 38 nm is obtained in the visible-wavelength range when the average power of pump light is 1.27 W. It is that injecting the pump light in deep anomalous dispersion regime contributes to such an efficient spectrally isolated CR. The mechanism during the forming of CR is discussed and the experimental results are in good agreement with the calculation.