Shortly after the world’s smallest laser that is 10 times smaller than the wavelength of light was produced by researchers at Norfolk State University in Virginia, researchers from the University of California, Berkeley have created the world’s smallest semiconductor laser, capable of generating visible light in a space smaller than a single protein molecule.
This marks a major milestone in laser physics, and heralds a new era in the field of optics.
What makes the latest advancement important is that researchers not only squeezed light into such a tight space but also succeeded in finding a novel way to keep that light energy from dissipating as it moved along, thereby achieving laser action. The results were published online in the journal Nature.
The two achievements shatter the traditional notion of laser limits: an electromagnetic wave cannot be focused beyond the size of half its wavelength.
Researchers have tried to break the laser limit by compressing light down to dozens of nanometers by binding it to the electrons that oscillate collectively at the surface of metals. This interaction between light and oscillating electrons is known as surface plasmons.
Researchers from Norfolk State University created lasing action through plasmons by using gold nanoparticles immersed in a dye. The dye coupled to the gold spheres generated surface plasmons when exposed to light.
But the biggest problem encountered by scientist working on plasmon lasers is in achieving the buildup of the electromagnetic field necessary for lasing. The resistance inherent in metals caused an almost immediate dissipation of surface plasmons.
Xiang Zhang, who led the team that worked on semiconductor laser, found a way to overcome this problem. He used a novel approach by to stem the loss of light energy by pairing a cadmium sulfide nanowire — 1,000 times thinner than a human hair — with a silver surface separated by an insulating gap of only 5 nanometers, the size of a single protein molecule. In this structure, the gap region stores light within an area 20 times smaller than its wavelength. Because light energy is largely stored in this tiny non-metallic gap, loss is significantly diminished.
There are several applications of plasmons: nanolasers that can probe, manipulate and characterize DNA molecules; optics-based telecommunications many times faster than current technology; and optical computing in which light replaces electronic circuitry with a corresponding leap in speed and processing power.