Parallel femtosecond laser direct writing in silica glass by multiple beams with different wavefront curvature

We present a parallel writing method in silica glass by multiple femtosecond laser beams. Collinear femtosecond laser beams with different wavefront curvature were incident on an objective lens and focused at different depths below the surface of silica glass. Hence multiple focal points exist in the glass simultaneously and parallel writing on multiple layers is realized. By adjusting the beam wavefront, the layer distance and the layer alignment can be changed. Our parallel writing method is useful to shorten the fabrication time of femtosecond laser direct writing.