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The laser micro-machining technology is an attractive alternative to conventional photoresist-based technologies for manufacturing terahertz (THz) cross-shaped mesh filters. It can address some limitations related to filter's quality, process complexity, unit cost and available materials. However, there are also open issues associated with the laser micro-machining technology that have to be addressed. In particular, some intrinsic characteristics of laser micro-machined structures, i.e. the side-wall tapering, that impact both achievable geometrical and dimensional accuracy and the filters’ performance. This research proposes a novel fabrication process, called laser precession machining, that addresses some of the key laser micro-machining limitations in producing THz mesh filters. It employs an ultrafast laser and a “precess” module to vary the beam incident angle and thus to minimise the taper angle on the sidewalls of the filters’ cross-shaped through holes. A significant reduction of this negative tapering effect was achieved on micro-structures produced with this new method that led to a significant improvement of filters’ performance. The filters’ performance was compared with the simulation results and they were in good agreement. X-ray photoelectron spectroscopy (XPS) analysis was carried out to analyze the effects of laser precession machining on the composition of copper substrates as a potential factor affecting the filters’ performance.
Bibliographical noteFunding Information:
XPS data collection was performed at the EPSRC National Facility for XPS (‘HarwellXPS’), operated by Cardiff University and UCL, under contract No. PR16195. The use of the 1.1 THz vector network analyser was funded by the EPSRC Strategic Equipment grant EP/P020615/1. Authors would like to thank Professor Michael Lancaster (University of Birmingham) for his supervision and doctor Stephen Hanham (University of Birmingham) for his help in measurements of the samples.
© 2021 Elsevier Ltd
- laser micro-machining
- mesh filter
- tapering effect
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Mechanical Engineering
- Electrical and Electronic Engineering
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