Using the strange properties of tiny particles of gold, researchers have concentrated light down smaller than a single atom, letting them look at individual chemical bonds inside molecules, and opening up new ways to study light and matter.
Single gold atoms behave just like tiny metallic ball bearings in our experiments, with conducting electrons roaming around, which is very different from their quantum life.
For centuries, scientists believed that light, like all waves, couldn’t be focused down smaller than its wavelength, just under a millionth of a metre. Now, researchers led by the University of Cambridge have created the world’s smallest magnifying glass, which focuses light a billion times more tightly, down to the scale of single atoms.
In collaboration with European colleagues, the team used highly conductive gold nanoparticles to make the world’s tiniest optical cavity, so small that only a single molecule can fit within it. The cavity – called a ‘pico-cavity’ by the researchers – consists of a bump in a gold nanostructure the size of a single atom, and confines light to less than a billionth of a metre. The results, reported in the journal Science, open up new ways to study the interaction of light and matter, including the possibility of making the molecules in the cavity undergo new sorts of chemical reactions, which could enable the development of entirely new types of sensors.
According to the researchers, building nanostructures with single atom control was extremely challenging. “We had to cool our samples to -260°C in order to freeze the scurrying gold atoms,” said Felix Benz, lead author of the study. The researchers shone laser light on the sample to build the pico-cavities, allowing them to watch single atom movement in real time.
“Our models suggested that individual atoms sticking out might act as tiny lightning rods, but focusing light instead of electricity,” said Professor Javier Aizpurua from the Center for Materials Physics in San Sebastian in Spain, who led the theoretical section of this work.
“Even single gold atoms behave just like tiny metallic ball bearings in our experiments, with conducting electrons roaming around, which is very different from their quantum life where electrons are bound to their nucleus,” said Professor Jeremy Baumberg of the NanoPhotonics Centre at Cambridge’s Cavendish Laboratory, who led the research.
The findings have the potential to open a whole new field of light-catalysed chemical reactions, allowing complex molecules to be built from smaller components. Additionally, there is the possibility of new opto-mechanical data storage devices, allowing information to be written and read by light and stored in the form of molecular vibrations.
Yale scientists have found a way to greatly boost the intensity of light waves on a silicon microchip using the power of sound.
Writing in the journal Nature Photonics, a team led by Peter Rakich describes a new waveguide system that harnesses the ability to precisely control the interaction of light and sound waves. This work solves a long-standing problem of how to utilize this interaction in a robust manner on a silicon chip as the basis for powerful new signal-processing technologies.
The prevalence of silicon chips in today’s technology makes the new system particularly advantageous, the researchers note. “Silicon is the basis for practically all microchip technologies,” said Rakich, who is an assistant professor of applied physics and physics at Yale. “The ability to combine both light and sound in silicon permits us to control and process information in new ways that weren’t otherwise possible.”
Rakich said combining the two capabilities “is like giving a UPS driver an amphibious vehicle — you can find a much more efficient route for delivery when traveling by land or water.”
More luminous and energy efficient than LEDs, white lasers look to be the future in lighting and Li-Fi, or light-based wireless communication
While lasers were invented in 1960 and are commonly used in many applications, one characteristic of the technology has proven unattainable. No one has been able to create a laser that beams white light.
Researchers at Arizona State University have solved the puzzle. They have proven that semiconductor lasers are capable of emitting over the full visible color spectrum, which is necessary to produce a white laser.
The researchers have created a novel nanosheet — a thin layer of semiconductor that measures roughly one-fifth of the thickness of human hair in size with a thickness that is roughly one-thousandth of the thickness of human hair — with three parallel segments, each supporting laser action in one of three elementary colors. The device is capable of lasing in any visible color, completely tunable from red, green to blue, or any color in between. When the total field is collected, a white color emerges.
The researchers, engineers in ASU’s Ira A. Fulton Schools of Engineering, published their findings in the July 27 issue of the journal Nature Nanotechnology. Cun-Zheng Ning, professor in the School of Electrical, Computer and Energy Engineering, authored the paper, “A monolithic white laser,” with his doctoral students Fan Fan, Sunay Turkdogan, Zhicheng Liu and David Shelhammer. Turkdogan and Liu completed their Ph.Ds. after this research.
The technological advance puts lasers one step closer to being a mainstream light source and potential replacement or alternative to light emitting diodes (LEDs). Lasers are brighter, more energy efficient and can potentially provide more accurate and vivid colors for displays like computer screens and televisions. Ning’s group has already shown that their structures could cover as much as 70 percent more colors than the current display industry standard.
Another important application could be in the future of visible light communication in which the same room lighting systems could be used for both illumination and communication. The technology under development is called Li-Fi for light-based wireless communication, as opposed to the more prevailing Wi-Fi, using radio waves. Li-Fi could be more than 10 times faster than current Wi-Fi, and white laser Li-Fi could be 10 to 100 times faster than LED based Li-Fi currently still under development.
“The concept of white lasers first seems counterintuitive because the light from a typical laser contains exactly one color, a specific wavelength of the electromagnetic spectrum, rather than a broad-range of different wavelengths. White light is typically viewed as a complete mixture of all of the wavelengths of the visible spectrum,” said Ning, who also spent extended time at Tsinghua University in China during several years of the research.
In typical LED-based lighting, a blue LED is coated with phosphor materials to convert a portion of the blue light to green, yellow and red light. This mixture of colored light will be perceived by humans as white light and can therefore be used for general illumination.
Sandia National Labs in 2011 produced high-quality white light from four separate large lasers. The researchers showed that the human eye is as comfortable with white light generated by diode lasers as with that produced by LEDs, inspiring others to advance the technology.
“While this pioneering proof-of-concept demonstration is impressive, those independent lasers cannot be used for room lighting or in displays,” Ning said. “A single tiny piece of semiconductor material emitting laser light in all colors or in white is desired.”
Princeton University researchers have developed a new method to increase the brightness, efficiency and clarity of LEDs, which are widely used on smartphones and portable electronics as well as becoming increasingly common in lighting.
Using a new nanoscale structure, the researchers, led by electrical engineering professor Stephen Chou, increased the brightness and efficiency of LEDs made of organic materials (flexible carbon-based sheets) by 57 percent. The researchers also report their method should yield similar improvements in LEDs made in inorganic (silicon-based) materials used most commonly today.
The method also improves the picture clarity of LED displays by 400 percent, compared with conventional approaches. In an article published online August 19 in the journal Advanced Functional Materials, the researchers describe how they accomplished this by inventing a technique that manipulates light on a scale smaller than a single wavelength.
“New nanotechnology can change the rules of the ways we manipulate light,” said Chou, who has been working in the field for 30 years. “We can use this to make devices with unprecedented performance.”
A LED, or light emitting diode, is an electronic device that emits light when electrical current moves through two terminals. LEDs offer several advantages over incandescent or fluorescent lights: they are far more efficient, compact and have a longer lifetime, all of which are important in portable displays.
Current LEDs have design challenges; foremost among them is to reduce the amount of light that gets trapped inside the LED’s structure. Although they are known for their efficiency, only a very small amount of light generated inside an LED actually escapes.
“It is exactly the same reason that lighting installed inside a swimming pool seems dim from outside – because the water traps the light,” said Chou, the Joseph C. Elgin Professor of Engineering. “The solid structure of a LED traps far more light than the pool’s water.”
Optical devices could bring natural light into dark, highly populated areas In dense, urban centers around the world, many people live and work in dim and narrow streets surrounded by tall buildings that block sunlight.
To alleviate the problem, Egyptian researchers have developed a corrugated, translucent panel that redirects sunlight onto narrow streets and alleyways. The panel is mounted on rooftops and hung over the edge at an angle, where it spreads sunlight onto the street below.