Fig. 1. Principle of fabricating tapered nano-holes via ring-lens-tailored Bessel beam’s energy peak. (a) Schematic illustrating the energy distribution along the z-axis of a ring-lens-tailored Bessel beam compared to a conventional axicon-based Bessel beam. Inset: the principle of generating a ring-lens-tailored Bessel beam. (b), (c) Diagram of nano-holes with/without tapers by the ring-lens-tailored Bessel beam. Insets: top-view scanning electron microscope (SEM) images.

Fig. 2. Schematic of generating the ring-lens-tailored Bessel beam. The Gaussian beam is shaped by an SLM loaded with a ring-lens phase and then passes through a lens (focal length of 500 mm) placed 500 mm after the SLM, finally forming a Bessel beam. Insets (left to right): Gaussian beam intensity, ring-lens phase, annular beam, and Bessel beam intensity distribution.

Fig. 3. Spatial energy distribution of a ring-lens-tailored Bessel beam. (a) Phase diagrams of ring-lenses with varying radii (R). (b) Simulated cross-sectional energy distributions of the annular beam in the x–y plane. (c) Experimental energy distributions of the annular beam in the x–y plane.

Fig. 4. Spatial energy distributions of ring-lens-tailored Bessel beams. (a) Simulated longitudinal energy distributions of ring-lens-tailored Bessel beams in the y–z plane. (b) Experimental energy distributions of ring-lens-tailored Bessel beams, showing a peak shift with increasing R.

Fig. 5. Adjusting tapers by varying ring-lens-tailored Bessel beams with different R. (a) Simulated energy distributions of Bessel beams with R of 1.25–2.50 mm. (b) Cross-sectional SEM images of nano-holes with/without tapers and schematic of the feature size of a nano-hole. (c) Top-view and cross-sectional SEM images of nano-holes. Dashed lines represent linear fittings to indicate the trend. (d)–(f) Illustrating how variation in R affects outer/inner diameter (d_in/d_out), taper depth (h₁), and taper angle (θ) of nano-holes.

Fig. 6. Fabrication of the nano-hole array. (a) Top-view SEM image of a 7 × 3 nano-hole array with tapers. (b) Statistical analysis of 20 nano-holes’ inner (d_in) and outer (d_out) diameters.