Creation of high-contrast structures in superpositions of higher order Bessel beams for laser processing of glasses

Bessel beams of the zeroth order are notorious for characteristic of having diffraction-less focal zone. Due to this property they became desirable for a number of laser micromachining applications, such as Bragg grating inscription, microchannel forming, photopolymerization and more [1] . By means of spatial light modulators or diffractive optical elements Bessel like beam variations with shaped transverse intensity distribution can be obtained which also proved beneficial in glass cleaving, for example [2] . Higher order Bessel beams also known as Bessel vortex beams also have interesting properties like carrying orbital angular momentum [3] . A combination of Bessel vortices of different topologies allows to form high width/depth ratio beams with complex transverse intensity distribution [4] , [5] . Such beams can be realized with geometrical phase elements which are manufactured by inscribing birefringent nanograting inside the bulk of fused silica [6] . By controlling retardance and the local angle of nanograting one can manufacture numerous beam shaping elements.