Filamentation Of Flattened Beam By Use Of Axicon In Fused Silica

It is important to control the femtosecond laser filamentation and the supercontinuum(SC)for their potential applications.The use of axicon is beneficial to the filamentation elongation and supercontinuum enhancement,because the axicon can convert the incident laser into a Bessel beam and forms a unique longer depth of focus region;On the other hand,without damaging the optical medium,the flattened laser beam which has a uniform distribution of the beam intensity,can propagate in condense media with a higher incident energy than that of Gaussian laser beam.It has unique advantages in forming a supercontinuum with high energy and high conversion efficiency.Therefore,the purpose of this paper is to combine the flattened beam with an axicon to achieve optimal control of filamentation and supercontinuum in fused silica.In this paper,the filamentation and supercontinuum radiation of flattened beam in fused silica after axicon are studied experimentally.First,the filamentation of Gaussian and flattened beam,respectively,with different energies in fused silica after passing through an axicon are studied.We compare and study the filamentation generated by the Gaussian beam and the flattened beam,respectively,with the same incident pulse energy(672 ?J).The results show that the flattened beam can generate longer filament with relative uniform intensity distribution in the focal depth of the axicon than that of the Gaussian beam.Second,the supercontinuum of Gaussian beams and flattened beams,respectively,at different energies in fused silica after passing through an axicon also were studied.The supercontinuum generated by the Gaussian beam of 672 ?J and the flattened beam of 672 ?J and 1.319 mJ are compared and studied.Through comparative analysis,it is concluded that,without damaging the medium,since the flattened beam can allow higher energy to be incident,the flattened beam can be generated to generate supercontinuum with a higher energy than that of the Gaussian beam in fused silica.The comparison of the spectra shows that the relative spectral intensity of flattened beam with 1.319 mJ in the range of 500-700 nm is much higher than that of the Gaussian beam with 672 ?J.The conversion efficiency of the Gaussian beam and the flattened beam is 32.58% and 39.59%,respectively.It can be seen that the flattened laser beam has advantages not only in generating long and uniform filament,but also in generating the intense SC.The combination of flattened beams and axicon is helpful to many applications,such as white light LIDAR and micro-nano processin.