New 10cm metalens may pave way for next

However, the team initially faced a challenge in designing larger metalens for astronomical imaging. 

"There is a major limitation with the lithography tool because these tools are used to make computer chips, so chip size is restricted to no more than 20 to 30 millimeters. In order to make a 100-millimeter diameter lens, we needed to find a way around this limitation," said Joon-Suh Park, who is the co-first author of the paper. 

To overcome this engineering challenge, the researchers used the DUV projection lithography technology to smoothly merge numerous "patterns of nanopillars." 

This approach shows that this technology can imprint 18.7 billion customized nanostructures onto a 10-centimeter circular surface in minutes.

"Using the same DUV projection lithography, one could produce large-diameter, aberration-correcting meta-optics or even larger lenses on larger glass diameter wafers as the corresponding CMOS foundry tools become increasingly available in the industry," said Soon Wei Daniel Lim, a postdoctoral fellow at SEAS and co-first author of the paper. 

The combination of these patterning and etching advancements enabled the development of all-glass metalens with improved imaging capabilities for astronomical observations.

The metalens could endure heat and cold conditions

The researchers showcased the effectiveness of the newly developed metalens in capturing images of nearby celestial objects within the visible wavelength range. 

The newly designed metalens was affixed on a tripod with a color filter and camera sensor at the roof of Harvard's Science Center. 

During the demonstration, the team successfully imaged the Sun, the Moon, and a faint nebula about 2,590 light years away from Earth. 

"We were able to get very detailed images of the Sun, the moon, and the nebula that are comparable to images taken by conventional lenses," said Arman Amirzhan, a graduate student in the Capasso Lab and co-author of the paper, in the release.

In a different experiment, the researchers just used the metalens to image a cluster of sunspots. Surprisingly, the generated image nearly resembled one acquired by NASA of the same sunspots on that very day.

Regarding its durability, the metalens demonstrates resilience by withstanding both extreme heat and cold conditions. Additionally, it exhibits the ability to endure the intense vibrations experienced during a space launch, ensuring no damage or deterioration in optical performance.

The findings have been detailed in the journal ACS Nano. 

Study abstract:

Metasurfaces, optics made from subwavelength-scale nanostructures, have been limited to millimeter-sizes by the scaling challenge of producing vast numbers of precisely engineered elements over a large area. In this study, we demonstrate an all-glass 100 mm diameter metasurface lens (metalens) comprising 18.7 billion nanostructures that operates in the visible spectrum with a fast f-number (f/1.5, NA = 0.32) using deep-ultraviolet (DUV) projection lithography. Our work overcomes the exposure area constraints of lithography tools and demonstrates that large metasurfaces are commercially feasible. Additionally, we investigate the impact of various fabrication errors on the imaging quality of the metalens, several of which are specific to such large area metasurfaces. We demonstrate direct astronomical imaging of the Sun, the Moon, and emission nebulae at visible wavelengths and validate the robustness of such metasurfaces under extreme environmental thermal swings for space applications.