A powerful laser can turn incandescent lamps into power-sippers, said optics researchers at the University of Rochester. The process could make a light as bright as a 100-watt lamp consume less electricity than a 60-watt lamp, while remaining cheaper and radiating a more pleasant light than fluorescent technologies.
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.
“We’ve been experimenting with the way ultra-fast 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 the University of 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 super-filament is a brief, intense beam of light called a femtosecond laser pulse. The laser burst lasts only a few quadrillionths of a second. To grasp 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 light can radiate from the filament.
“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.”
Despite the intensity involved, the femtosecond laser can be powered by a wall outlet, meaning that when the process is refined, implementing it to augment regular light bulbs should be relatively simple.
In addition to increasing the brightness of a bulb, Guo’s process can be used to tune the color of the light. In 2008, his team used a similar process to change the color of nearly any metal to blue, gold, gray and black. 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 even has been able to make a filament radiate partially polarized light, which until now has been impossible without filters that reduce the bulb’s efficiency.
The team is now working to discover what other aspects of a common light bulb they might be able to control.