High-NA Focusing of Ultrashort Laser Pulses in Bulk of ZnSe

A study of high-NA focusing process of ultrashort laser pulses in bulk of ZnSe has been carried out. It is shown that when focusing laser Gaussian beam with high-aperture lenses into a transparent medium aberration distortions occur leading to an increase in focal spot size. The results of experimental studies on ablation of front and back surfaces of a plane-parallel plate with 4 mm thickness made of ZnSe by laser pulses with a duration of 0.3, 1, 10 ps and a wavelength of 1030 nm focused by a micro lens ( NA = 0.55) are presented. It is shown that at low pulse energies focusing can be considered in a linear mode in which focal spot size is due to aberration distortions.