Statistical properties of ultrafast supercontinuum generated by femtosecond Gaussian and Bessel beams: a comparative study

We present a comparative experimental study of spectral broadening and supercontinuum (SC) generation in 3-mm-thick sapphire crystal using 800 nm, 130 fs pulses in low-numeric-aperture focused Gaussian and axicon-generated Bessel beam geometry. Despite the markedly higher input energy used in the case of the Bessel beam, the dynamics of spectral broadening appears to be very similar in both cases, eventually producing a flat SC spanning across the visible and near-infrared spectral range with low shot-to-shot fluctuations (standard deviation ≤1%) of the spectral intensity. The statistical analysis performed at different stages of the spectral broadening reveals that shot-to-shot fluctuations of the spectral intensity are associated with four-wave-mixing-induced spectral correlations.