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New One-step Fabrication Technique Yields Ultrathin Flat Lenses

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An international team of researchers has developed a method of fabricating high-performance lenses in monolayer two-dimensional transitional metal dichalcogenide (TMDC) material using a femtosecond laser. The lens has a subwavelength resolution and a focusing efficiency of 31%, which marks a step closer to ultimately thin optical devices for use in nano-optics and on-chip photonic applications.

The team, led by Baohua Jia of the Swinburne University of Technology, Qiaoliang Bao formerly of Monash University, and Chengwei Qiu of the National University of Singapore, discovered that it is possible to generate nanoparticles by using a femtosecond laser beam to interact with the monolayer TMDC material, which is significantly different from the process produced by a continuous-wave laser.
Schematic of femtosecond laser fabrication of a monolayer TMDC lens. Inset: (i) AFM image of a monolayer TMDC single crystal, and (ii) Schematic of femtosecond laser-induced generation of MOx nanoparticles. Courtesy of Han Lin et al.
Schematic of femtosecond laser fabrication of a monolayer TMDC lens. Inset: (i) AFM image of a monolayer TMDC single crystal, and (ii) schematic of femtosecond laser-induced generation of MOx nanoparticles. Courtesy of Han Lin et al.


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The technique, Jia said, opens up new possibilities in the fabrication of photonic devices, as the method is scalable. The technique is a one-step process and does not require a vacuum or other special environments.

Because the laser pulse is so short, the material remains cold, allowing the nanoparticles to attach firmly to the substrate. The nanoparticles showed strong scattering to modulate the amplitude of light, which allows the lens to provide high efficiency and subwavelength resolution. The team was then able to demonstrate diffraction-limited imaging using the lenses.

“We have used the thinnest material in the world to fabricate a flat lens, and prove that the good performance of the ultrathin lens can lead to a high-resolution image,” said Han Lin, first author on the study.

Though lenses made from multilayer TMDCs have been demonstrated before, when their thickness is reduced to the subnanometer scale, their insufficient phase or amplitude modulation results in focusing efficiencies of less than 1%.

“It shows enormous potential in different applications, such as eyeglasses, microscopy lenses, telescopes, and camera lenses,” Lin said. “It is foreseeable that by using this technique, the weight and size of camera lenses can be significantly reduced in the near future.”

The research was published in Light: Science & Applications (www.doi.org/10.1038/s41377-020-00374-9).

Published: August 2020
Glossary
chalcogenide
Chalcogenide refers to a class of compounds containing elements from group 16 of the periodic table, which includes sulfur (S), selenium (Se), and tellurium (Te). These elements are known as chalcogens. Chalcogenides are typically formed by combining one or more chalcogens with other elements, such as metals or metalloids. Chalcogenides are of particular interest in materials science and technology due to their unique properties, which include: Semiconductor behavior: Many chalcogenides...
metalens
A metalens, short for "metasurface lens," is a type of optical lens that uses nanostructured materials to manipulate light at a subwavelength scale. Unlike traditional lenses made of glass or other transparent materials, metalenses do not rely on the curvature of their surface to refract or focus light. Instead, they use carefully engineered patterns of nanostructures, such as nanoscale antennas or dielectric structures, to control the phase and amplitude of light across the lens's surface....
lens
A lens is a transparent optical device that focuses or diverges light, allowing it to pass through and form an image. Lenses are commonly used in optical systems, such as cameras, telescopes, microscopes, eyeglasses, and other vision-correcting devices. They are typically made of glass or other transparent materials with specific optical properties. There are two primary types of lenses: Convex lens (converging lens): This type of lens is thicker at the center than at the edges. Convex...
Research & TechnologyOpticschalcogenidedichalcogenidestransitional metal dichalcogenideTMDCnano-opticfemtosecond lasersoptical fabricationmetalensultrathin opticslenslensesImagingTech Pulse

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