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A molecular scale Fresnel lens! Now we can create retro style nano-projectors, even if the transparency will be thicker than the lens.
by biomcgary 11y ago
A molecular scale Fresnel lens! Now we can create retro style nano-projectors, even if the transparency will be thicker than the lens.
- tgb 11y agoIs it really a Fresnel lens? I was thinking it was more of a diffraction grating. The paper describes it as > The 3D focusing is a result of the interferences of wavelets originated in the lens plane from different zones19, as illustrated in Fig. 1d. Which suggests it's more about interference than about Snell's law.
- graycat 11y agoThat was my guess, too.
- frozenport 11y agoThings with rings are generally called Fresnel lenses, even if its not about interference, see: https://en.wikipedia.org/wiki/Zone_plate https://en.wikipedia.org/wiki/Zone_plate
- dTal 11y agoFresnel zone plate, yes. Fresnel lens, no; they are not lenses. This does look like a microscopic zone plate. This is not a new idea though, it's how we focus X-rays as most materials don't refract X-rays very well; I guess they just managed to make a really small one. I wonder in what sense it "breaks the diffraction limit".
- crispyambulance 11y agoIt does not "break" the diffraction limit. The title is inaccurate. The actual paper doesn't say they've broken the diffraction limit. They only achieve a subwavelength focal point. I'll make an attempt to mansplain this... The actual diffraction limit depends on wavelength (lamda) and the numerical aperture (NA) of the lens. Diffraction limit is ~ lamda/(2*NA). In traditional objective lenses used in confocal scanning microscopes, the diffraction limit has been ~0.5 microns. If you increase NA, it also means decreasing working distance-- to the point where the focal point meets the surface of the lens. They've managed to increase NA with their zone plate, but since their "lens" thickness is "200 nm", they still have a useable working distance.