Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.
Macroscopic optics is (relatively) easy to talk about since we literally see it every day. From eyeglasses to rainbows, we have many examples of large-scale light manipulation via reflections and refractions. Of course, the manufacture of these things presents their own challenges of precision and strength. But when we get to smaller and smaller scales, our intuitions fall apart and we need new tools to talk about the world of nano-optics If you thought the effort it took to grind out a perfect glass lens was tough, then buckle up for what’s to come. Let’s take a tour of some topics in this field to see the wonders it can convey unto us if we look hard enough.
It is hard to view an object that is destroyed, yet oftentimes scientists best view into the nano-world is through hitting it with particles, seeing how it reacted, and backtracking the aftermath to develop the general picture of what we had before. If our target of interest was not destroyed, then the normal operating conditions are altered and though multiple passes we can build a picture as well. Obviously, it’s not an ideal process and so when scientists announced a way to use microwaves to not only observe nano-objects but also preserve their status, it was intriguing and full of promise (Levy, Bello).
With a liquid material surrounding our nano-object, a thin membrane (8-50 nanometers in thickness) allows us to examine the contents without directly interacting with it. Using a microwave nanoscope to send microwaves into the chamber, it records the reflected or deflected waves, building up a picture of the nano-object though a 3-D rotation of this. These waves are “100 million times weaker than those of a home microwave oven” and are emitted in opposite directions to ensure that no damaging effects such as heat can occur. This is especially important as the process could be used to image living things like cells and biological processes, potentially revealing the actual mechanisms scientists have pondered for centuries (Ibid).
Trying to make an image with conventional technology has a drawback many don’t consider: Our image isn’t perfect. Because of the material used to collect the light rays, the beams passing through it gets diffracted and not all the light waves that enter the lens make it to our eyes. These evanescent waves, if captured, would allow amazing detail to be achieved but how would one bring them back into the fold?
Work by Sir John B. Pendry (Imperial College London) has shown how such a capture could be achieved with metamaterials combined in such a way to create a hyperlens capable of grabbing those evanescent waves and projecting them to our eyes. Some have been developed but are incredibly cost-prohibitive and are also restricted to such a narrow field-of-view that you must use precision in placing your object underneath the lens. This can be challenging if you don’t know what your object even looks like, so it seems as though it defeats the purpose. A team from the Pohang University of Science and Technology did find a way to mass-produce “a scalable and reliable fabrication process of a large scale hyperlens” using a hexagonal array which does show eventual promise of the desired result scientists are aiming for…eventually (Jung).
Vacuuming with Light
It sounds nuts, because it is, but scientist have developed a system for extracting nanoparticles from an environment. Unlike a traditional vacuum cleaner, which creates suction as air flow draws inward pressure, this system would implement optical pressure via a dielectric microparticle designed to be an equilateral cuboid with nanoscale holes in them. Only 2 opposite sides will be cored, leaving the hole as more of a tunnel through the cuboid. Upon light being shined on the face of the cuboid, the hole creates optical pressure and any nanoparticles inside it becomes trapped. It is hoped that someday this could be used as an array of different cuboids developed onto a chip and the capacity for multiple nanoparticle collections to happen at once can be achieved (Sdelnikov).
Hidden from Us
One new way to image things on the nanoscale involves a technique known as synthetic wavelength holography and it offers a way to see things not in our direct line of sight. It has to do with scattered light, the result of photons bouncing off objects it encounters. If one had a way to collect these scattered photons and undo that effect, one could in principle see the original object. To do this, laser beams at different wavelengths are sent, bounce off something to hit our target, then bounce back and return to us. Knowing the interference pattern from these beams allows us to fix a distance of the object from us. Knowing this and the ability to capture fast frame rates allowed scientists to deconstruct the interference exhibited and gather an image of the hidden object (Ogasa).
Bello, Mark. “New microwave imaging approach opens a nanoscale view on processes in liquids.” Innovations-report.com. innovations-report, 16 Mar. 2016. Web. 13 Aug. 2019.
Jung, YunMee. “Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging.” Innovations-report.com. innovations-report, 24 Apr. 2017. Web. 13 Aug. 2019.
Levy, Dawn. “ORNL-NIST team explores nanoscale objects and processes with microwave microscopy.” Innovations-report.com. innovations-report, 22 Mar. 2016. Web. 13 Aug. 2019.
Ogasa, Nikk. "Out of Sight." Scientific American. Scientific American, Feb. 2022. Print. 14-5.
Sdelnikov. “Optical vacuum cleaner can manipulate nanoparticles.” Innovations-report.com. innovations report, 10 Sept. 2019. Web. 31 Aug. 2020.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2021 Leonard Kelley