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Metasurfaces have been made, but the problem is that they usually are static and for quantum optic applications the question is how to make a rapidly configurable metasurface. for this Harvard has initiated a multidisciplinary team that involves theoretical physics, metamaterials, nanophotonic circuitry, quantum devices, plasmonics, nanofabrication, and computational modeling

Reading "wavefront engineering" in the title I thought it had to do with wave manipulation in the sea. Nothing to do though. As I read further in this article, Harvard thrives in forming multidisciplinarity groups. Their practice is to call the best team in each expertise they need to merge. Not one researcher from each discipline, but teams of experienced professors and a series of graduate students. Maybe we could discuss it in the retreat!

Physicists in the US have made the first ultrathin flat lens. Thanks to its flatness, the device eliminates optical aberrations that occur in conventional lenses with spherical surfaces. As a result, the focusing power of the lens also approaches the ultimate physical limit set by the laws of diffraction.

Really nice indeed! The new flat ultrathin lens is different in that it is a nanostructured "metasurface" made of optically thin beam-shaping elements called optical antennas, which are separated by distances shorter than the wavelength of the light they are designed to focus. These antennas are wavelength-scale metallic elements that introduce a slight phase delay in a light ray that scatters off them. The metasurface can be tuned for specific wavelengths of light by simply changing the size, angle and spacing between the nanoantennas. "The antenna is nothing more than a resonator that stores light and then releases it after a short time delay," Capasso says. "This delay changes the direction of the light in the same way that a thick glass lens would." The lens surface is patterned with antennas of different shapes and sizes that are oriented in different directions. This causes the phase delays to be radially distributed around the lens so that light rays are increasingly refracted further away from the centre, something that has the effect of focusing the incident light to a precise point.

Great engineering feat from Capasso's idea - an integrated flat lens electrically controlled enabling dynamic beam steering. Reconfigurabilility is the aim. The lens can be used microscope systems, holographic and projection imaging, LIDAR and laser printing. Besides working now on the mid-IR, visible light is the target.

If you have 45 minutes and you want to learn a bit about inverse design of metasurfaces using machine learning, then I would highly recommend this talk. I found it very easy to follow both the physics and machine learning parts of it.

An intelligent (that is, self-adaptive) cloak driven by deep learning. Quite cool, eh? Something we can get inspired by?