First immersion metalens unveiled


Rebecca Pool

Thursday, May 11, 2017 - 16:30
Image: Immersion meta-lens in a commercial scanning confocal microscope [Capasso Lab/Harvard SEAS]
Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences, US, claim to have developed the first flat lens for immersion microscopy.
The researchers have integrated the immersion metalens into a commercial scanning confocal microscope, achieving a spatial resolution of approximately 200 nm.
Designed for any liquid, the lens is set to provide a cost-effective and easy-to-manufacture alternative to hand polishing lenses for immersion objectives.
“This new lens has the potential to overcome the drawbacks and challenges of lens-polishing techniques that have been used for centuries,” says Professor Federico Capasso from Applied Physics at Harvard SEAS. 
The array of titanium dioxide nanofins can be tailored for any immersion liquid [Capasso Lab].
As Capasso highlights, he and his team designed a front planar lens that can be easily tailored and manufactured for different liquids with different refractive indices.
The lens is made up of an array of titanium dioxide nanofins and fabricated using a single-step lithographic process.  
“These lenses are made using a single layer of lithography, a technique widely used in industry,” highlights Wei Ting Chen, postdoctoral fellow at Harvard SEAS.  “They can be mass-produced with existing foundry technology or nanoimprinting for cost-effective high-end immersion optics.”
Using this process, the team designed metalenses that can not only be tailored for any immersion liquid but also for multiple layers of different refractive indices.
This is especially important for imaging biological material, such as skin.   
“Our immersion meta-lens can take into account the refractive indices of epidermis and dermis to focus light on the tissue under human skin without any additional design or fabrication complexity,” explains Alexander Zhu, graduate student at Harvard SEAS.
The researchers reckon the immersion metalenses will be used in many biological imaging applications, will enable entirely new applications, and eventually outperform conventional lenses in existing markets.
Research is published in Nano Letters.
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