CityU’s Novel metalens revolutionises conventional Vacuum UV optics technology

A research team co-led by City University of Hong Kong (CityU) have successfully developed a novel Vacuum Ultra-Violet (VUV) meta-lens which can generate and focus the VUV light, a disruptive technology for the UV optics market.

VUV is used in semiconductor manufacturing, photochemistry and materials science. The focused VUV light source is strongly needed for nanolithography, material processing, advanced manufacturing, and other industrial areas.

However, it has been costly to work with. VUV with wavelengths between 100 to 200 nanometres (nm), is strongly absorbed by the oxygen in air, and VUV's application requires a vacuum chamber or other specialised environment. Conventionally, very bulky and expensive systems with special and rare nonlinear crystals are used for generating and focusing of VUV light.

Limitations and challenges of applying VUV light

In addition, virtually almost all types of glass used for conventional lenses are unsuitable for the VUV due to their strong absorption in this region. The few VUV-transmittable materials currently used for lenses are comparably fragile, placing practical limits on thin lens fabrication and design.

To address the above limitations, Professor Tsai Din-ping, Chair Professor of the Department of Electrical Engineering (EE), and Dr Chen Mu-Ku, Research Assistant Professor of EE, have designed and fabricated many of a 150nm length triangle shape zinc oxide nano-antenna to form a VUV metalens.

"We have developed a meta-lens with intricate nano-structures on zinc oxide thin film. It is capable of focusing VUV light. This metalens provides a compact method for nonlinear VUV generation and focusing of the generated light," said Professor Tsai, one of the corresponding authors of the paper recently published in the academic journal Science Advances titled "Vacuum ultraviolet nonlinear metalens".

The new VUV metalens in a 45 micro-meter (µm) diameter can convert UV light with 394nm wavelength into VUV light with 197nm wavelength, and focuses the VUV light on a small spot less than 2 micro-metre in diameter. Tests at Rice University demonstrated a focused light spot with an enhanced power density by 21 times.

Technology breakthrough revolutionises the market of UV optics

"Our VUV meta-lens is compact, lightweight, effective, and can be mass produced by semiconductor electronics fabrication process. This novel and disruptive meta-device could revolutionise the conventional VUV optics technology and its market," Professor Tsai said.

The meta-lens allows substantial streamlining of VUV system design and facilitating more advanced applications. This work provides a useful platform for developing low-loss VUV components and increasing the accessibility of the VUV regime.

This research is funded by the Area of Excellence Project (AoE), University Grants Committee/Research Grants Council of Hong Kong SAR government. Professor Tsai is the Project Coordinator of the AoE project "Meta-optics, Meta-acoustics and Meta-devices".

Co-authors of the paper include Professor Naomi Halas, Professor Peter Nordlander, Dr Michael Semmlinger, Dr Zhang Ming, Catherine Arndt, Dr Benjamin Cerjan and Dr Yang Jian of Rice University; Dr Tseng Ming-Lun of Taiwan's National Yang Ming Chiao Tung University; Dr Huang Tzu-Ting and Dr Chu Cheng-Hung of Academia Sinica in Taiwan; Dr Kuo Hsin-Yu of National Taiwan University; and Dr Su Vin-Cent of National United University in Taiwan.

https://www.cityu.edu.hk/research/stories/2022/06/16/cityus-novel-metalens-revolutionises-conventional-vacuum-uv-optics-technology