Macroscale Microfabrication Enabled by Nanoscale Morphological Control of Laser Internal Modification

Over the past decades, ultrafast laser internal modification has become a widely adopted approach to enable three-dimensional (3D) micromachining of transparent materials into sophisticated structures and devices with the extreme geometrical flexibility. Owing to the linear diffraction and nonlinear self-focusing effects, it is extremely challenging to maintain the high longitudinal resolution when focusing deeply into the transparent substrates for achieving macroscale microfabrication, i.e., fabrication of objects of centimeter-level heights without sacrificing the micrometer-scale resolution. We overcome this tremendous difficulty using loosely focused picosecond laser pulses, which, surprisingly, offer focal-volume-invariant modification deeply inside fused silica glass and give rise to the formation of extended nanocracks preferentially oriented along the laser scan direction. We show that the combination of these two advantages uniquely allows efficient macroscale microfabrication as demanded by various applications such as 3D glass printing and flow chemistry.