Harvard researchers integrated an immersion meta-lens into a commercial scanning confocal microscope, achieving an imaging spatial resolution of approximately 200 nm. (Image courtesy of the Capasso Lab/Harvard SEAS)

The first ever flat lens for immersion microscopy may enable a more cost-effective and easily manufactured alternative to current immersion microscopes.

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences have developed the new lens that they hope will provide a better option than the centuries-old technique of 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,” Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS, and senior author of the paper, said in a statement.

Optical microscopes collect scattered light through a series of lenses and reconstruct it into an image. However, the fine detailed geometrical information of an object is carried by the portion of scattered light propagating at wide angles, making the image difficult to be captured.

Immersion microscopes use a layer of liquid—usually either water or oil—between the specimen slide and the objective lens to reduce the angles and allow for the capturing of light. The front lens—the smallest and most important component—is only a few millimeters in size and needs to be hand polished because of its distinctive shape.

The researchers used nanotechnology to design the front planar lens—made of an array of titanium dioxide nanofins and fabricated using a single-step lithographic process—that can be tailored and manufactured for different liquids with different refractive indices.

“These lenses are made using a single layer of lithography, a technique widely used in industry,” Wei Ting Chen, first author of the paper and postdoctoral fellow at SEAS, said in a statement. “They can be mass-produced with existing foundry technology or nanoimprinting for cost-effective high-end immersion optics.”

The team also designed metalenses that can be tailored for multiple layers of different refractive indices, which could be important for imaging biological material including 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,” Alexander Zhu, co-author of the paper and a graduate student at SEAS, said in a statement.

The study was published in Nano Letters.