Filamentation Of Femtosecond Lasers Via Space-modulation In Fused Silica

In recent years,with the development of ultrafast optics,the phenomenon of plasma filaments generated when femtosecond lasers are transmitted in nonlinear media has attracted people's attention.Because of its important application value in many fields,it has become an important research direction of nonlinear optics.In different application fields,the requirements for the spectral enhancement of multi-filamentation control and its accompanying supercontinuum radiation are needed.Therefore,this paper combines the femtosecond laser flattened beam and the microlens array to achieve uniform distribution in fused silica.Multifilament arrays and modulation of the distribution pattern of the multifilament arrays;concurrent supercontinuum radiation produced with the multifilament array was investigated.Firstly,by using a laser beam shaping system consisted of aspherical lenses,Gaussian intensity distribution of initial femtosecond laser beam is converted to a flat-top distribution.In order to better illustrate the changes in filamentation and supercontinuum radiation before and after shaping,comparisons have been made in experiments.Our experimental results show that,compared with the filaments formed by a Gaussian laser beam,the filaments formed by the flattened beam have a more uniform distribution and almost the same onset owing to the initial uniform energy distribution across the section of the laser beam.Secondly,in this paper,the supercontinuum generation of Gaussian and flattened beam by microlens array is studied.Compared with the case of the Gaussian laser beam,higher incident laser pulse energy is allowed in the case of flattened laser beam,and consequently stronger supercontinuum generation is obtained.The approach provides a way to obtain high power femtosecond supercontinuum source which is of great importance in many applications.