Within the frame of high precision ultrafast laser processing of transparent materials, we report here on the use of adaptive optics as a tool for intra-volume laser engraving of glass. With the active monitoring of the laser beam wavefront, the repartition of the above-threshold energy in the focal volume is actively detected. Therefore, the elongation of the laser-induced modification due to longitudinal spherical aberration can be minimized or emphasized on demand. Indeed, the industrial adaptive optics set up, made of a wavefront sensor and a deformable mirror, permits the management of each wavefront aberration as RMS values of chosen Zernike polynomials coefficients. This technique allows the control of the processing of transparent dielectrics, whatever the index of refraction and the depth are.
This study addresses the precise correlation between wavefront distortions and intra-volume modifications in borosilicate glass obtained with a 300 fs Yb-doped fiber laser running at 1030 nm. The effects of the 3rd and 5th orders of longitudinal spherical aberrations on the laser-induced marking of the bulk are investigated with the purpose of precisely controlling the length of the interaction volume in the illuminated dielectric material. We show here a minimization of the total length of the marking by 65% at 600 µm in depth, from the natural wavefront to the optimized one, close to the diffraction limit.