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. 2023 Dec 18;14(12):2256.
doi: 10.3390/mi14122256.

Precise Focal Spot Positioning on an Opaque Substrate Based on the Diffraction Phenomenon in Laser Microfabrication

Xian Jing  1   2 , Pengju Zhao  2 , Fuzeng Wang  2 , Mingkun Han  2 , Jieqiong Lin  2
Affiliations

Precise Focal Spot Positioning on an Opaque Substrate Based on the Diffraction Phenomenon in Laser Microfabrication

Xian Jing et al. Micromachines (Basel). .

Abstract

The precise positioning of the laser focal spot on the substrate is an important issue for laser microfabrication. In this work, a diffraction pattern-based focal spot positioning method (DFSPM) is proposed to achieve the precise positioning of the laser focal spot on opaque substrates. A series of diffraction patterns of laser focus under-positioning, exact positioning and over-positioning were obtained to investigate the cross-section light distribution of the laser focal spot. According to the monotonic tendency of FWHM to exhibit light intensity at the focal spot cross-section away from the focal plane, the FWHM threshold of polynomial fitted curves was used to determine the exact positioning of laser focus. The ascending scanning method was used to obtain the diffraction patterns at various vertical positions and the FWHM threshold of light distribution at the exact position. The polynomial fitted curves verify the FWHM monotonic tendency of light intensity distribution at the focal spot cross-section along the optical axis. Precise positioning can be achieved with a 100 nm adjustment resolution. This work was expected to provide references for laser microfabrication on opaque materials.

Keywords: diffraction patterns; focal spot positioning; laser microfabrication; opaque substrate; two-photon lithography.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic diagram of DFSPM. (a) DFSPM setups. (b) Focal spot variation.
Figure 2
Figure 2
The microrods fabricated by the ascending scanning method. (a) Schematic diagram of the ascending scan method at a cross-sectional view. (b) Images of microrods fabricated with the rise in the focal spot at z-direction. The scale bar is 10 μm.
Figure 3
Figure 3
Normalized intensity curves of the focal spot central cross-section at various z-positions. The blue hollow dots represent the detected light intensity data of the focal spot while the red curves represent the fitting curves. (a-I–f-VI) The intensity curves of focal spot when the focus position gradually ascending along the z-axis with a 100 nm interval.
Figure 4
Figure 4
Microrods fabricated with the chosen diffraction pattern. The scale bar is 2 μm.
See this image and copyright information in PMC

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