Optimization of ultrafast laser parameters for 3D micromachining of fused silica

• Published in: Optics and laser technology 2020-03, Vol.123, p.105933, Article 105933
• Main Authors: Dogan, Yusuf, Madsen, Christi K.
• Format: Article
• Language: English
• Subjects: 3D microfabrication; Chemical etching; Configurations; Direct laser writing; Direct writing; Fused silica; Lasers; Micromachining; Optimization; Organic chemistry; Parameters; Pulse duration; Repetition; Roughness; Selectivity; Silicon dioxide; Surface properties; Surface roughness; Ultrafast laser; Ultrafast lasers
• ISSN: 0030-3992; 1879-2545
• DOI: 10.1016/j.optlastec.2019.105933

•Optimal laser parameters after etching were found for high quality optical devices.•A smoothness of 21.8 nm for 1 mm2 area in silica was achieved.•1.25 m/s scan rate for a system operating with a 2 MHz repetition rate was proved.•Complex writing involving surfaces at different orientations was simplified. We present an optimization study on laser parameters for 3D micromachining of fused silica to achieve critical goals for practical applications including high surface quality, high volume production, and complex surfaces by ultrafast laser direct writing assisted chemical etching. We conducted experiments on laser pulse width of 300 fs and 1 ps, pulse energy ranging from 0.1 µJ to 1.6 µJ, three different polarizations (circular, parallel and perpendicular) and number of overlapped pulses from 3 to 10,000 at 1030 nm with up to 2 MHz repetition rate to investigate their effect on nanogratings and one dimensional (1D) channel and two dimensional (2D) planar surface selective etching on 1 mm thick fused silica. In one configuration, we achieved 21.8 nm RMS surface roughness with 80 µm Gaussian filtering and in another configuration, we estimated the maximum writing speed to be 1.25 m/s for given 2 MHz repetition rate with less than 400 nm filtered root mean square (RMS) surface roughness at a 1 mm2 area which covers the thickness of the glass.