A Metalens with a Near-Unity Numerical Aperture

Area of Science:

• Optics and Photonics
• Metasurface Technology
• Nanophotonics

Background:

• Large numerical aperture (NA) lenses are crucial for applications needing small light-matter interaction volumes or large angular collection.
• Traditional large NA lenses rely on bulky, expensive refractive optics.
• Existing flat optics and metasurfaces have been limited to NA values below 0.9.

Purpose of the Study:

• To demonstrate a new approach for creating ultraflat, high-NA lenses.
• To achieve a diffraction-limited flat lens with near-unity NA and subwavelength thickness.
• To showcase the imaging capabilities of the developed flat lens.

Main Methods:

• Numerical simulations and experimental fabrication of a novel diffractive flat lens.
• Design utilizing diffractive elements capable of bending light at angles up to 82°.
• Testing the lens in a confocal configuration for imaging applications.

Main Results:

• Achieved a diffraction-limited flat lens with a numerical aperture (NA) greater than 0.99.
• The lens exhibits subwavelength thickness (approximately λ/3) and operates with unpolarized light.
• Successfully demonstrated imaging of color centers in diamond nanocrystals.

Conclusions:

• The developed diffractive flat lens surpasses the performance of traditional optical elements and existing flat optics.
• This approach circumvents efficiency drops associated with standard phase-mapping techniques.
• Represents a significant advancement in flat optics for high-resolution imaging and light manipulation.