Focusing light with a metal film coated patchy particle

Abstract

Microsphere-assisted super-resolution imaging is a promising technique that can significantly enhance the resolution of conventional optical microscopes. The focus of a classical microsphere is called photonic nanojet, which is a symmetric high-intensity electromagnetic field. Recently, patchy microspheres have been reported to have superior imaging performance than pristine microspheres, and coating microspheres with metal films leads to the formation of photonic hooks, which can enhance the imaging contrast of microspheres. Understanding the influence of metal patches on the near-field focusing of patchy particles is important for the rational design of a nanostructured microlens. In this work, we theoretically and experimentally showed that the light waves can be focused and engineered using patchy particles. When coating dielectric particles with Ag films, light beams with a hook-like structure or S-shaped structure can be generated. Simulation results show that the waveguide ability of metal films and the geometric asymmetry of patchy particles cause the formation of S-shaped light beams. Compared with classical photonic hooks, S-shaped photonic hooks have a longer effective length and a smaller beam waist at far-field region. Experiments were also carried out to demonstrate the generation of classical and S-shaped photonic hooks from patchy microspheres.

Characteristics of photonic nanojet generated by patchy microspheres

“…Through formula (7) to formula (10) and their series, the solution of any field function can be obtained, and the scattering problem of any particle can be solved.…”

“…This thin film can image the sample surface and can be used as a contact optical element, which can improve the super-resolution ability of traditional microscopes 6 . In 2023, Chu et al theoretically and experimentally proved that when dielectric microspheres are coated with an Ag film, a hook-like light beam or an "S"-shaped light beam can be generated 7 . With the correct design of the required silver film, photonic hooks and "S"-shaped photonic hooks can be generated from patchy microcylinders or patchy microspheres.…”

Analysis of the impact of edge diffraction on the manipulation of photonic nanojets and photonic hooks using an energy-based model in diffraction-based structures

“…PNJs have excellent field enhancement and the ability to break through diffraction limits [3], while PHs provide an innovative method for generating a bending field, with a currently known minimum curvature radius smaller than wavelength [4]. Therefore, PNJs and PHs have attracted great attention, and several typical methods have been proposed to generate and modulate them, including geometric design [5][6][7][8][9], adjustment of incidence [10][11][12], application of additional masks [13][14][15][16][17], and so on. PNJs and PHs have shown application potential in fields such as terahertz devices [18], sensors [19], bio-medicine [20], cellular and particle manipulation [21][22][23], super-resolution imaging [24,25], and so on.…”

Photonic Hook-Assisted Contrast-Enhanced Super-Resolution Imaging Using Janus Microspheres

“…For instance, patchy microspheres with metallic surface coatings can block a portion of incoming light, resulting in an asymmetric illumination effect. Their capacity of PH generation has been theoretically and experimentally demonstrated [15], [16], [17]. One of the most important applications of PHs is in super-resolution imaging [18], [19].…”