Abstract
Different responses for the front (entrance) and the rear (exit) surfaces of fused silica processed with femtosecond laser pulses at 807 nm were observed under tight focusing conditions (NA = 0.4). The morphology of the surface in the beam path is highly sensitive to the focus position. By adjusting the focus position, we can produce not only a submicrometer cavity but also a submicrometer bubble. We achieved higher-quality micromachining and a better spatial resolution (400 nm) by focusing the laser beam at the rear surface rather than at the front surface.
Highlights
The ultrashort pulse laser is becoming a powerful tool for micromachining and microfabrication [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
Different responses for the front and the rear surfaces of fused silica processed with femtosecond laser pulses at 807 nm were observed under tight focusing conditions (NA = 0.4)
The morphology of the surface in the beam path is highly sensitive to the focus position
Summary
The ultrashort pulse laser is becoming a powerful tool for micromachining and microfabrication [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. The shorter time scale for energy coupling into the material reduces the destructive thermal effect, which further leads to higher spatial resolution in surface ablation of metals and semiconductors [6,7]. When a femtosecond laser pulse is focused on a largebandgap transparent material, the intensity in the focal volume becomes high enough to cause nonlinear absorption such as multiple photon absorption (MPA). MPA leads to a much smaller absorption volume than that of single photon absorption, and it results in a much higher spatial resolution [8,9]. The modifications in the bulk of transparent materials under tight focusing conditions have been studied [13,14]. The higher resolution of ablation on the surface of a transparent medium may be achieved because of the smaller size of the focal region. To our knowledge this probability has not been studied systematically
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