Inhibition and enhancement of linear and nonlinear optical effects by conical phase front shaping for femtosecond laser material processing

Abstract

The emergence of high-powered femtosecond lasers presents the opportunity for large volume processing inside of transparent materials, wherein a myriad of nonlinear optical and aberration effects typically convolves to distort the focused beam shape. In this paper, convex and concave conical phase fronts were imposed on femtosecond laser beams and focussed into wide-bandgap glass to generate a vortex beam with tuneable Gaussian-Bessel features offset from the focal plane. The influence of Kerr lensing, plasma defocussing, and surface aberration on the conical phase front shaping were examined over low to high pulse energy delivery and for shallow to deep processing tested to 2.5 mm focussing depth. By isolating the underlying processes, the results demonstrate how conical beams can systematically manipulate the degree of nonlinear interaction and surface aberration to facilitate a controllable inhibition or enhancement of Kerr lensing, plasma defocussing, and surface aberration effects. In this way, long and uniform filament tracks have been generated over shallow to deep focussing by harnessing surface aberration and conical beam shaping without the destabilizing Kerr lensing and plasma defocussing effects. A facile means for compressing and stretching of the focal interaction volume is presented for controlling the three-dimensional micro- and nano-structuring of transparent materials.

From Localized Laser Energy Absorption to Absorption Delocalization at Volumetric Glass Modification with Gaussian and Doughnut-Shaped Pulses

“…Irreversible local modification of glasses created by the impact of ultrashort laser pulses, which is manifested as an increase in the refractive index [1][2][3][4][5], is used in many applications based on direct writing of three-dimensional structures, such as waveguides [1,[6][7][8], waveplates [9,10], Bragg gratings [11][12][13], optical memories [14][15][16], computer-generated holograms [17], and microfluidic devices [18,19]. From its first demonstration [1], this technique has attracted considerable attention from researchers due to its importance for existing and emerging technologies.…”

Laser nano-filament explosion for enabling open-grating sensing in optical fibre

“…Hole diameters of ~200 nm diameter have been demonstrated in glasses by Kerr lensing, and axicon optics [38][39][40][41][42][43] . Our group has further harnessed surface aberration of glass plates to form similarly long filament tracks in bulk glass 44 . This approach was extended into optical fibre by using RI-matching fluid to eliminate astigmatism of the cylindrical fibre shape and generate filament arrays having first-order Bragg stopbands [45][46][47] .…”