Harvard researchers have brought he world one step closer to knowing the joys granted by invisibility cloaks, with a breakthrough in developing metamaterials that can bend light in odd ways.
Creating metamaterials has been tough until now, since they require suspended metal dots. But researchers have found a way, using “extremely short and powerful laser pulses to create three-dimensional patterns of tiny silver dots within a material,” according to a press release.
Their process was outlined in the journal Applied Physics Letters. It moves nanoscale metal lithography into three dimensions, and at a resolution high enough to be usable for metamaterials. Use of the materials in a potential invisibility cloak works through its 3D structure (a lot of other methods out there work through optical illusions).
“If you want a bulk metamaterial for visible and infrared light, you need to embed particles of silver or gold inside a dielectric, and you need to do it in 3D, with high resolution,” said lead author Kevin Vora, a graduate student at the Harvard School of Engineering and Applied Sciences (SEAS), in a press release.
“This work demonstrates that we can create silver dots that are disconnected in x, y, and z,” Vora said. “There’s no other technique that feasibly allows you to do that. Being able to make patterns of nanostructures in 3D is a very big step towards the goal of making bulk metamaterials.”
Vora works with a laboratory alongside Eric Mazur, Balkanski Professor of Physics and Applied Physics at SEAS, who has used a femtosecond laser to study how focused bursts of light can “change the electrical, optical, and physical properties of a material,” states the release.
“When a conventional laser shines on a transparent material, the light passes straight through, with slight refraction. The femtosecond laser is special because it emits a burst of photons as bright as the surface of the sun in a flash lasting only 50 quadrillionths (5 × 10-14) of a second. Instead of shining through the material, that energy gets trapped within it, exciting the electrons within the material and achieving a phenomenon known as nonlinear absorption,” it states.
This tracks the energy in pockets where a chemical reaction can take place, which then alters the material’s structure. This has been used before for 2D and 3D mental nanofabrication.
“Normally, when people use femtosecond lasers in fabrication, they’re creating a wood pile structure: something stacked on something else, being supported by something else,” explains Mazur. “If you want to make an array of silver dots, however, they can’t float in space.”
[box_light]Photos courtesy of Eliza Grinnell, Harvard SEAS. Graphic courtesy of Kevin Vora[/box_light]