Flat Lens Boost Virtual Reality

Metalensesflat surfaces that use nanostructures to focus light — promise to revolutionize optics by replacing the bulky, curved lenses currently used in optical devices with a simple, flat surface.  But, these metalenses have remained limited in the spectrum of light they can focus well Now a team of researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has developed the first single lens that can focus the entire visible spectrum of light — including white light — in the same spot and in high resolution. This has only ever been achieved in conventional lenses by stacking multiple lenses.

Focusing the entire visible spectrum and white light – combination of all the colors of the spectrum — is so challenging because each wavelength moves through materials at different speeds. Red wavelengths, for example, will move through glass faster than the blue, so the two colors will reach the same location at different times resulting in different foci. This creates image distortions known as chromatic aberrations.

Cameras and optical instruments use multiple curved lenses of different thicknesses and materials to correct these aberrations, which, of course, adds to the bulk of the device.

Metalenses have advantages over traditional lenses,” says Federico Capasso, Professor of Applied Physics at SEAS and senior author of the research. “Metalenses are thin, easy to fabricate and cost effective. This breakthrough extends those advantages across the whole visible range of light. This is the next big step. Using our achromatic lens, we are able to perform high quality, white light imaging. This brings us one step closer to the goal of incorporating them into common optical devices such as cameras“.

The research is published in Nature Nanotechnology.

Source: https://www.seas.harvard.edu/

Nanofiber For Bullet Proof Vests

Harvard researchers have developed a lightweight, portable nanofiber fabrication device that could one day be used to dress wounds on a battlefield or dress shoppers in customizable fabrics. There are many ways to make nanofibers. These versatile materials — whose target applications include everything from tissue engineering to bullet proof vests — have been made using centrifugal force, capillary force, electric field, stretching, blowing, melting, and evaporation.

Each of these fabrication methods has pros and cons. For example, Rotary Jet-Spinning (RJS) and Immersion Rotary Jet-Spinning (iRJS) are novel manufacturing techniques developed in the Disease Biophysics Group at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute for Biologically Inspired Engineering. Both RJS and iRJS dissolve polymers and proteins in a liquid solution and use centrifugal force or precipitation to elongate and solidify polymer jets into nanoscale fibers. These methods are great for producing large amounts of a range of materials – including DNA, nylon, and even Kevlar – but until now they haven’t been particularly portable.

The Disease Biophysics Group recently announced the development of a hand-held device that can quickly produce nanofibers with precise control over fiber orientation. Regulating fiber alignment and deposition is crucial when building nanofiber scaffolds that mimic highly aligned tissue in the body or designing point-of-use garments that fit a specific shape.

nanofiber

Our main goal for this research was to make a portable machine that you could use to achieve controllable deposition of nanofibers,” said Nina Sinatra, a graduate student in the Disease Biophysics Group and co-first author of the paper. “In order to develop this kind of point-and-shoot device, we needed a technique that could produce highly aligned fibers with a reasonably high throughput.

The new fabrication method, called pull spinning, uses a high-speed rotating bristle that dips into a polymer or protein reservoir and pulls a droplet from solution into a jet. The fiber travels in a spiral trajectory and solidifies before detaching from the bristle and moving toward a collector. Unlike other processes, which involve multiple manufacturing variables, pull spinning requires only one processing parameter — solution viscosity — to regulate nanofiber diameter. Minimal process parameters translate to ease of use and flexibility at the bench and, one day, in the field.

The research was published recently in Macromolecular Materials and Engineering.

Source: https://www.seas.harvard.edu/

Reconfigurable Materials

Metamaterialsmaterials whose function is determined by structure, not composition — have been designed to bend light and sound, transform from soft to stiff, and even dampen seismic waves from earthquakes. But each of these functions requires a unique mechanical structure, making these materials great for specific tasks, but difficult to implement broadly. But what if a material could contain within its structure, multiple functions and easily and autonomously switch between them?

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Wyss Institute of Biologically Inspired Engineering at Harvard University have developed a general framework to design reconfigurable metamaterials. The design strategy is scale independent, meaning it can be applied to everything from meter-scale architectures to reconfigurable nano-scale systems such as photonic crystals, waveguides and metamaterials to guide heat.

In terms of reconfigurable metamaterials, the design space is incredibly large and so the challenge is to come up with smart strategies to explore it,” said Katia Bertoldi, John L. Loeb Associate Professor of the Natural Sciences at SEAS and senior author of the paper. “Through a collaboration with designers and mathematicians, we found a way to generalize these rules and quickly generate a lot of interesting designs.”

The research is published in Nature.

How To Manipulate Light

Electrons are so 20th century. In the 21st century, photonic devices, which use light to transport large amounts of information quickly, will enhance or even replace the electronic devices that are ubiquitous in our lives today. But there’s a step needed before optical connections can be integrated into telecommunications systems and computers: researchers need to make it easier to manipulate light at the nanoscale.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have done just that, designing the first on-chip metamaterial with a refractive index of zero, meaning that the phase of light can travel infinitely fast.

This new metamaterial was developed in the lab of Eric Mazur, the Balkanski Professor of Physics and Applied Physics and Area Dean for Applied Physics at SEAS, and is described in the journal Nature Photonics.

manipulated light

New zero-index material made of silicon pillar arrays embedded in a polymer matrix and clad in gold film creates a constant phase of light, which stretches out in infinitely long wavelengths

Light doesn’t typically like to be squeezed or manipulated but this metamaterial permits you to manipulate light from one chip to another, to squeeze, bend, twist and reduce diameter of a beam from the macroscale to the nanoscale,” said Mazur. “It’s a remarkable new way to manipulate light.”

Although this infinitely high velocity sounds like it breaks the rule of relativity, it doesn’t. Nothing in the universe travels faster than light carrying information — Einstein is still right about that. But light has another speed, measured by how fast the crests of a wavelength move, known as phase velocity. This speed of light increases or decreases depending on the material it’s moving through.

When light passes through water, for example, its phase velocity is reduced as its wavelengths get squished together. Once it exits the water, its phase velocity increases again as its wavelength elongates. How much the crests of a light wave slow down in a material is expressed as a ratio called the refraction index — the higher the index, the more the material interferes with the propagation of the wave crests of light. Water, for example, has a refraction index of about 1.3.

When the refraction index is reduced to zero, really weird and interesting things start to happen.

Source: https://www.seas.harvard.edu

Injectable 3D Vaccine Fights Cancer and HIV

One of the reasons cancer is so deadly is that it can evade attack from the body’s immune system, which allows tumors to flourish and spread. Scientists can try to induce the immune system, known as immunotherapy, to go into attack mode to fight cancer and to build long lasting immune resistance to cancer cells. Now, researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University and Harvard’s School of Engineering and Applied Sciences (SEAS) show a non–surgical injection of programmable biomaterial that spontaneously assembles in vivo into a 3D structure could fight and even help prevent cancer and also infectious disease such as HIV. Their findings are reported in Nature Biotechnology.

dentritic cells
A microscope image shows many of the immune system’s dendritic cells that were collected from a 3D scaffold three days after in vivo injection. The 3D scaffold effectively recruits and activates the dendritic cells to trigger an immune response against specific cells, such as cancerous cells

We can create 3D structures using minimally–invasive delivery to enrich and activate a host’s immune cells to target and attack harmful cells in vivo,” said the study’s senior author David Mooney, Ph.D., who is a Wyss Institute Core Faculty member and the Robert P. Pinkas Professor of Bioengineering at Harvard SEAS. “Nano–sized mesoporous silica particles have already been established as useful for manipulating individual cells from the inside, but this is the first time that larger particles, in the micron–sized range, are used to create a 3D in vivo scaffold that can recruit and attract tens of millions of immune cells,” said co-lead author Jaeyun Kim, Ph.D., an Assistant Professor of Chemical Engineering at Sungkyunkwan University (Korea) and a former Wyss Institute Postdoctoral Fellow.
Source: http://wyss.harvard.edu/

Infrared, A Renewable Energy

Physicists from Harvard University propose a device to capture energy from earth”s infrared emissions to outer space. When the sun sets on a remote desert outpost and solar panels shut down, what energy source will provide power through the night? A battery, perhaps, or an old diesel generator? Perhaps something strange and new.
Physicists at the Harvard School of Engineering and Applied Sciences (SEAS) envision a device that would harvest energy from Earth’s infrared emissions into outer space. Heated by the sun, our planet is warm compared to the frigid vacuum beyond. Thanks to recent technological advances, the researchers say, that heat imbalance could soon be transformed into direct-current (DC) power, taking advantage of a vast and untapped energy source.

It’s not at all obvious, at first, how you would generate DC power by emitting infrared light in free space toward the cold,” says principal investigator Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard SEAS. “To generate power by emitting, not by absorbing light, that’s weird. It makes sense physically once you think about it, but it’s highly counterintuitive. We’re talking about the use of physics at the nanoscale for a completely new application.”
Their analysis of the thermodynamics, practical concerns, and technological requirements have been published in the Proceedings of the National Academy of Sciences.

Source: http://www.seas.harvard.edu/

How To Print Tiny Batteries

3D printing can now be used to print lithium-ion microbatteries the size of a grain of sand. The printed microbatteries could supply electricity to tiny devices in fields from medicine to communications, including many that have lingered on lab benches for lack of a battery small enough to fit the device, yet provide enough stored energy to power them.

To make the microbatteries, a team based at Harvard University and the University of Illinois at Urbana-Champaign printed precisely interlaced stacks of tiny battery electrodes, each less than the width of a human hair.
3D printing battery
For the first time, a research team from the Wyss Institute at Harvard University and the University of Illinois at Urbana-Champaign demonstrated the ability to 3D-print a battery. This image shows the interlaced stack of electrodes that were printed layer by layer to create the working anode and cathode of a microbattery.
Not only did we demonstrate for the first time that we can 3D-print a battery, we demonstrated it in the most rigorous way,“said Jennifer Lewis, Ph.D., senior author of the study, who is also the Hansjörg Wyss Professor of Biologically Inspired Engineering at the Harvard School of Engineering and Applied Sciences (SEAS), and a Core Faculty Member of the Wyss Institute for Biologically Inspired Engineering at Harvard University. Lewis led the project in her prior position at the University of Illinois at Urbana-Champaign, in collaboration with co-author Shen Dillon, an Assistant Professor of Materials Science and Engineering there.
The results were published in today’s online edition of Advanced Materials.

Source: http://wyss.harvard.edu/

How To Create Artificial Nano Flowers

With the hand of nature trained on a beaker of chemical fluid, the most delicate flower structures have been formed in a Harvard laboratory—and not at the scale of inches, but microns. These minuscule sculptures, curved and delicate, don’t resemble the cubic or jagged forms normally associated with crystals, though that’s what they are. Rather, fields of carnations and marigolds seem to bloom from the surface of a submerged glass slide, assembling themselves a molecule at a time.By simply manipulating chemical gradients in a beaker of fluid, Wim L. Noorduin, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS) and lead author of a paper appearing on the cover of Science, has found that he can control the growth behavior of these crystals to create precisely tailored structures.
nano tulip
For at least 200 years, people have been intrigued by how complex shapes could have evolved in nature. This work helps to demonstrate what’s possible just through environmental, chemical changes,” says Noorduin.
Source: https://www.seas.harvard.edu/

Revolutionary Ultrathin, Flat Lens

Applied physicists at the Harvard School of Engineering and Applied Sciences (SEAS) have created an ultrathin, flat lens that focuses light without imparting the distortions of conventional lenses. At a mere 60 nanometers thick, the flat lens is essentially two-dimensional, yet its focusing power approaches the ultimate physical limit set by the laws of diffraction.
Operating at telecom wavelengths (i.e., the range commonly used in fiber-optic communications), the new device is completely scalable, from near-infrared to terahertz wavelengths, and simple to manufacture. The results have been published online in the journal Nano Letters.

A new ultrathin, flat lens focuses light without imparting the optical distortions of conventional lenses.

Our flat lens opens up a new type of technology,” says principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS. “We’re presenting a new way of making lenses. Instead of creating phase delays as light propagates through the thickness of the material, you can create an instantaneous phase shift right at the surface of the lens. It’s extremely exciting.
This breakthrough could lead to smart phones as thin as a credit card. “In the future we can potentially replace all the bulk components in the majority of optical systems with just flat surfaces,” says lead author Francesco Aieta, a visiting graduate student from the Università Politecnica delle Marche in Italy. “It certainly captures the imagination.”

Source: http://www.seas.harvard.edu/news-events/press-releases/flat-lens-offers-perfect-image