Elliptical nanohole arrays improve the beaming effect of plasmonic metalenses

A recent study in Optical Materials investigates the beam effect of a plasmonic metal lens with elliptical arrays of nanoholes in a metal film using experimental techniques and geometric simulations. The rotation of the elliptical major axis affects the size and polarization state of the transmitted light due to the birefringent effect of the elliptical nanohole. The polarization state of metals affects the resulting diffraction pattern.

The beam effect of plasmonic metals is influenced by ohmic losses. In this study, researchers analyzed the beam effect under the influence of ohmic losses using linearly transmitted light in the visible and near-ultraviolet range.

Potential of plasmonic metals in light transmission

The plasmonic metasurfaces provide transmitted light with characteristic phase, amplitude, and polarization states. A metal lens is a metasurface that changes the optical properties of transmitted light. Changing the periodicity of a nanostructure creates the beam effect when light passes through a nanoslit enclosed in a nanostructure.

Rotating the nanoaperture as the light hits it helps control the polarization of the transmitted light. The plasmonic metal lens grasps the radiative effect of transmitted light. Nanoapertures and nanopillars modify the polarization of light emanating from nanostructures.

The plasmonic metalens creates an artificial phase to maximize the spatial interference of the transmitted light. This planar lens effectively increases the focal spot size and depth of field compared to a traditional lens.

Proper spatial arrangement of nano-apertures such as optical vortices and non-diffracting rays can create a planar metal lens with exceptional optical properties.

Ohmic loss of metal films and beam effect of plasmonic metals

Photonics applications range from visible to near-ultraviolet (NUV) regimes. The visible and NUV domains are used for lithography and optical manipulation.

For optical applications, an optical beam with a sharply focused spot and a favorable working distance is required. Rotational notches in metal films have been studied for their optical properties based on their geometric design.

No research has examined the ohmic loss of metal films to study the radiative effect of plasmonic metals both through simulation and experimentation.

Metal films show different ohmic losses when light of different wavelengths is irradiated. The optical properties of plasmonic metals vary significantly between the NUV and visible wavelengths. The wavelength and thickness of the incident light affect the ohmic loss of a metal.

Investigation of optical properties of plasmonic metals with elliptical nanohole arrays

change et al. studied the optical properties of plasmonic metals in the visible and NUV region. The plasmonic metalens created an optical beam with a pinpoint spot.

Researchers proposed a new plasmonic metal composed of two concentric elliptical nanohole arrays. All elliptical nanoholes in the concentric arrays had the same size and number of nanoholes in the outer and inner concentric arrays.

Researchers studied the radiating effect of the metals’ transmitted light by varying the thickness and rotation of the elliptical nanoholes. The rotation of the elliptical major axis and the thickness of the metal film were used to explain the polarization state of the transmitted light.

study results

This study used computational and experimental techniques to study the beam effect of metals with different wavelengths and geometric shapes.

Metalens, which consisted of two elliptical concentric arrays filled with nanoholes, offered flexible polarization that enabled the generation of different beam shapes. The geometric shape of the metal lenses controlled the polarization state of the light it transmitted.

Researchers created two orthogonal polarizations with the IOPE design. The convergent optical transmission of the metal lenses was made possible by these two orthogonal polarizations. In this study, researchers also presented an approach to tuning the wavelength of metals from the point of view of ohmic loss.

The light in the metallic nanohole behaved like an FP effect for incident light in the visible spectrum. This showed that the FP resonance had the highest transmission intensity. Light in the metallic nanohole had high optical absorption for incident light in the NUV region and lacked a noticeable FP resonance. However, some special applications (such as lithography and phototherapy) require light with high transmission intensity in the NUV range. Silver thickness was increased to control the transmitted polarization by arranging geometric shapes for specific purposes.

Possibility of using proposed metals in optical applications

The total optical transmission from metals was about 17% for the IOPE. The focal area of ​​the IOPE had an optical transmission of only 2%. Increasing the number of elliptical nanoholes improved optical transmission. The nano-apertures in the metal film had reduced focusing efficiency because the metal film was opaque. However, the nano-apertures of metals had wavelength-selective capabilities and greater signal-to-noise ratio. This made it possible to use these metal lenses in maskless lithography applications.

Relation

Chang, C.-K., & Yeh, W.-T. (2022) Ray effect of the plasmonic metals patterned with concentric elliptical nanohole arrays. Optical Materials, 134113084. https://www.sciencedirect.com/science/article/pii/S0925346722011211

Disclaimer: The views expressed herein are those of the author, expressed in his own capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork, the owner and operator of this site. This disclaimer is part of the terms of use of this website.