To give people a sense of the problem, Shih describes it like the difference between off-roading and driving down a freshly paved highway.
“Unless you actively control your steering wheel, you’re not going to control your vehicle if you’re driving over rocky terrain,” he said. “If you want the wave to travel in a certain direction, you need it to travel in that direction without anything knocking it off the road.”
By growing the silver in a single crystalline form, Shih and Sanders eliminated the gaps – essentially building a smooth highway that keeps more of the surface plasmon polaritons moving in a similar direction along the plane of the semiconductor-silver interface.
But the smooth silver film also helped contain the photons that produce the laser activity within a smaller active field. In fact, it helped confine those photos in a space smaller than the wavelength of light.
That solved another problem for nanolaser development, an issue called the three-dimensional diffraction limit.
To sustain lasing, a nanolaser has to keep photons within its active field, where they can interact with excited atoms to produce more photons, said Gennady Shvets, a UT physics professor who carried out the theoretical modeling and testing for the project, along with two of his graduate students.
Before the smooth silver film, devices as tiny as UT’s nanolaser couldn’t contain enough photons within the active field, so the device wouldn’t produce enough new photons and the lasing would grind to a halt. The film helps confine photons within a volume smaller than their wavelength, a feat that allowed researchers to build a smaller device, use a less-intense pumping laser to start the process, and generate a continuous wave.
The next challenge is bringing this whole process up to room temperatures, Shvets and Shih said. Because of the small size and energy involved to pump the nanolaser in its current form, the process must occur at very cold temperatures.
Some types of nanolasers already work at room temperature, but they typically don’t create the plasmonic effects that work especially well on a planar semiconductor.
That will involve some experimentation with various materials, designs and sizes, Shvets said. “It’s probably as small as it’s going to get,” he said. “What would be really nice is to make this device work at room temperature.”<< previous 1 2