Laser Zap Brightens Bulbs
ROCHESTER, N.Y., June 1, 2009 -- Firing a beam from an ultrapowerful laser onto the filament of an incandescent bulb can double its brightness without increasing its energy consumption, according to optics researchers at the University of Rochester.
The laser process creates a unique array of nano- and microscale structures on the surface of a regular tungsten filament — the tiny wire inside a light bulb — and these structures make the tungsten become far more effective at radiating light. The process could make a light as bright as a 100-W bulb consume less electricity than a 60-W bulb while remaining far cheaper and radiating a more pleasant light than a fluorescent bulb can.
Chunlei Guo in front of his femtosecond laser, which can double the efficiency of a regular incandescent light bulb. (Photo: University of Rochester)
"We've been experimenting with the way ultrafast lasers change metals, and we wondered what would happen if we trained the laser on a filament," said Chunlei Guo, associate professor of optics at Rochester. "We fired the laser beam right through the glass of the bulb and altered a small area on the filament. When we lit the bulb, we could actually see this one patch was clearly brighter than the rest of the filament, but there was no change in the bulb's energy usage."
The key to creating the superfilament is an ultrabrief, ultraintense beam of light called a femtosecond laser pulse. The laser burst lasts only a few quadrillionths of a second. To get a grasp of that kind of speed, consider that a femtosecond is to a second what a second is to about 32 million years.
During its brief burst, Guo's laser unleashes as much power as the entire grid of North America onto a spot the size of a needle point. That intense blast forces the surface of the metal to form nanostructures and microstructures that dramatically alter how efficiently can radiate from the filament.
In 2006, Guo and his assistant, Anatoliy Vorobeyv, used a similar laser process to turn any metal pitch black. The surface structures created on the metal were incredibly effective at capturing incoming radiation, such as light.
"There is a very interesting 'take more, give more' law in nature governing the amount of light going in and coming out of a material," says Guo. Since the black metal was extremely good at absorbing light, he and Vorobyev set out to study the reverse process — that the blackened filament would radiate light more effectively as well.
"We knew it should work in theory," Guo said, "but we were still surprised when we turned up the power on this bulb and saw just how much brighter the processed spot was."
In addition to increasing the brightness of a bulb, Guo's process can be used to tune the color of the light as well. In 2008, his team used a similar process to change the color of nearly any metal to blue, golden, and gray, in addition to the black he'd already accomplished. Guo and Vorobeyv used that knowledge of how to control the size and shape of the nanostructures — and thus what colors of light those structures absorb and radiate — to change the amount of each wavelength of light the tungsten filament radiates. Though Guo cannot yet make a simple bulb shine pure blue, for instance, he can change the overall radiated spectrum so that the tungsten, which normally radiates a yellowish light, could radiate a more purely white light.
Guo's team has even been able to make a filament radiate partially polarized light, which until now has been impossible to do without special filters that reduce the bulb's efficiency. By creating nanostructures in tight, parallel rows, some light that emits from the filament becomes polarized.
The team is now working to discover what other aspects of a common light bulb they might be able to control. Fortunately, despite the incredible intensity involved, the femtosecond laser can be powered by a simple wall outlet, meaning that when the process is refined, implementing it to augment regular light bulbs should be relatively simple.
The findings will be published in an upcoming issue of the journal Physical Review Letters.
Guo is also announcing this month in Applied Physics Letters a technique using a similar femtosecond laser process to make a piece of metal automatically move liquid around its surface, even lifting a liquid up against gravity.
This research was supported by the US Air Force Office of Scientific Research.
For more information, visit: www.rochester.edu
- femtosecond laser
- A type of ultrafast laser that creates a minimal amount of heat-affected zones by having a pulse duration below the picosecond level, making the technology ideal for micromachining, medical device fabrication, scientific research, eye surgery and bioimaging.
- 1. With respect to radiation, a device used to attenuate particular wavelengths or frequencies while passing others with relatively no change. 2. See digital filter.
- Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
- The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
- The emission and/or propagation of energy through space or through a medium in the form of either waves or corpuscular emission.
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