Generation of subdiffraction longitudinal bifoci by shaping a radially polarized wave

Area of Science:

• Optics and Photonics
• Nanotechnology
• Materials Science

Background:

• Lenses with multiple focal points along the optical axis are crucial for various advanced optical applications.
• Achieving subdiffraction focusing, especially in the longitudinal direction, presents significant challenges due to diffraction limits.

Purpose of the Study:

• To propose and demonstrate a novel method for generating subdiffraction longitudinal bifoci using binary-phase bifocal super-oscillatory lenses (SOLs).
• To investigate the feasibility of controlling the distance between bifoci and their optical field characteristics.

Main Methods:

• Designed binary-phase bifocal SOLs by performing an AND operation between two single-foci SOLs with distinct focal lengths.
• Simulated the optical performance of three bifocal SOLs with a radius of 70λ at a wavelength of 118.8µm.

Main Results:

• Achieved subdiffraction longitudinal bifoci with Full Width at Half Maximum (FWHM) values ranging from 0.397λ to 0.449λ, below the Abbe diffraction limit of 0.510λ.
• Maintained low sidelobe ratios (<15.1%) and demonstrated controllable focal distances by adjusting single-foci SOL parameters.
• Generated bifoci with relatively uniform intensity and a strong longitudinal electric field.

Conclusions:

• The proposed binary-phase bifocal SOLs effectively generate subdiffraction longitudinal bifoci with tunable properties.
• The strong longitudinal electric field and ease of fabrication make these bifocal SOLs highly promising for optical imaging, particle acceleration, and other applications.