Supercontinuum Generation in Barium Fluoride Using Bessel Beams

We investigate supercontinuum generation using femtosecond duration pulses in a 15 mm long barium fluoride crystal using an axicon-generated Bessel beam. Spectral profiles of the generated supercontinuum are measured using axicon lenses of different cone angles, and with two different incident beam diameters. Our measurements reveal that the spectral profile is, indeed, dependent on the distance between the crystal and the tip of axicon, and also on incident laser power. We observe both modulated and smooth spectral profiles as the axicon cone angle is changed. Our experimental observations manifest the variation of the input laser intensity along the propagation axis in the crystal. The spectrum is found to be smoothest when the crystal is kept in physical contact with the tip of the axicon. The spectral extent is broadest for the highest axicon cone angle.