Polarisation-independent ultrafast laser selective etching processing in fused silica

In fused silica, ultrafast laser assisted etching enables high chemical etching rates (>300 mu m h(-1)) by setting a light polarisation linear and perpendicular to the beam writing direction. However, for many non-planar surfaces and 3D structures, dynamic polarisation control is difficult or not yet possible to implement. In this contribution, we identify a laser inscription regime in which high etching rates are accomplished independently of the light polarisation. In this regime (<15 pulses per mu m), we measure etching rates similar to 300 mu m h(-1) (4 hours in NaOH) including femtosecond-pulse energies corresponding to type II modifications. Few pulse inscriptions show a low degree of anisotropy as compared to higher number of pulses, thus enabling the polarisation insensitivity whose mechanisms are discussed. To demonstrate the capabilities of the processing, we fabricate curved and square-wave microchannels together with a complex 3D geometrical structure (stellated octahedron) containing an inter-plane arrangement with challenging angles (45 degrees), which are difficult to achieve even employing dynamic polarisation control.

Automated summary

In fused silica, ultrafast laser assisted etching achieves high etching rates (>300 μm h(-1)) by adjusting the light polarisation. However, for non-planar surfaces and 3D structures, achieving dynamic polarisation control is difficult. In this study, a laser inscription regime is identified to achieve high etching rates independently of light polarisation. The capabilities of this processing are demonstrated through the fabrication of curved and square-wave microchannels, as well as a complex 3D geometrical structure.