Scientists create tiny laser using silver nanoparticles

Scientists in Finland have paved the way for a new breed of ultrafast nanoscale lasers. Researchers at Aalto University have created a laser that works at such minuscule scales, the light can bounce back and forth just a few hundred times.The plasmic laser generates visible light waves using dark lattice modes, a first.

Most lasers rely on mirrors to generate the feedback signal necessary for laser light. The nano laser uses radiative coupling between silver nanoparticles, instead. The laser-generating nanoparticles are arranged in a periodic array, each particle — measuring just 100 nanometers across — acts as a tiny antenna.

The input energy necessary to trigger laser light is provided by organic fluorescent molecules. Because the laser light wavelengths and the spacing between nanoparticles match, the array radiates in unison.

Tiny lasers can be tremendously useful in science, but they can also be extremely difficult to work with. In this case, laser light created at such small scales can be too short-lived to be useful.

Researchers skirted the problem by using what are called “dark modes.”

“A dark mode can be intuitively understood by considering regular antennas: A single antenna, when driven by a current, radiates strongly, whereas two antennas — if driven by opposite currents and positioned very close to each other — radiate very little,” researcher Paivi Torm said in a news release. “A dark mode in a nanoparticle array induces similar opposite-phase currents in each nanoparticle, but now with visible light frequencies.”

Researchers also found a unique way to let light escape the confines of the tiny array.

“By utilizing the small size of the array, we found an escape route for the light,” explained Ph.D. student Heikki Rekola. “Towards the edges of the array, the nanoparticles start to behave more and more like regular antennas that radiate to the outer world.”