Abstract
Temporal focusing of spatially chirped femtosecond laser pulses overcomes previous limitations for ablating high aspect ratio features with low numerical aperture (NA) beams. Simultaneous spatial and temporal focusing reduces nonlinear interactions, such as self-focusing, prior to the focal plane so that deep (~1 mm) features with parallel sidewalls are ablated at high material removal rates (25 µm3 per 80 µJ pulse) at 0.04-0.05 NA. This technique is applied to the fabrication of microfluidic devices by ablation through the back surface of thick (6 mm) fused silica substrates. It is also used to ablate bone under aqueous immersion to produce craniotomies.
Highlights
Micromachining with femtosecond laser pulses, in which the transient generation of a plasma leads to the ablation of material [1], is a powerful technique to cut chemically inert media such as glass
We have demonstrated the use of temporal focusing with low numerical aperture beams for femtosecond micromachining
This geometry mitigates nonlinear interactions such that material can be ablated through large path lengths of optically transparent material
Summary
Micromachining with femtosecond laser pulses, in which the transient generation of a plasma leads to the ablation of material [1], is a powerful technique to cut chemically inert media such as glass. Successive pulses must focus through debris created by earlier pulses, and the pulses interact with the walls of the structure as the feature becomes deeper. This leads to a tapering of the feature that limits the aspect ratio [2,3]
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