May 24, 2021

Creating the next generation of lasers: The future is nano

Image shows the normalized surface plasmon polariton mode field distribution in the graphene nanoribbon plasmonic resonator in the electric spaser.

When the first laser was invented in 1960, it was described as “A solution looking for a problem, but before long, scientists harnessed its distinctive qualities — coherent, structured light with the ability to form a narrow beam with almost single wavelength — for a myriad of technological and medical applications.

But lasers are limited to the mesoscopic and the macro worlds due to a fundamental physical limit known as the diffraction limit. So, Professor Malin Premaratne from the Department of Electrical and Computer Systems Engineering, Monash University, is developing a new quantum electrodynamics theory to model nanoscale light sources that can generate highly coherent, nanoscale light-like fields. 

“A spaser – short for surface plasmon amplification by stimulated emission of radiation – is a nanolaser,” says Premaratne. “It provides coherent energy in the nanoscale by emitting a new particle called a plasmon, which originates from interactions of photons with electrons in materials. Unlike photons in laser light, plasmons can probe and roam the nanoworld.” 

Spasers allow probing atoms and molecules or exchange information between nanodevices, “whatever you can do with lasers in the micro world, now you can do it in the nanoworld,” he says.

Making spasers isn’t easy. Premaratne and his American colleague Prof. Mark Stockman, inventor of the spaser technology, are developing the theories behind how spasers work through complex modelling. To do that, they have to write their own software and algorithms requiring extraordinary computing power. “We don’t use existing software, we develop novel algorithms and mathematically clever ways to model these systems,” says Premaratne.

“Simulating these nanodevices is a highly computationally costly exercise. So we have to have supercomputing capability to do it,” Premaratne says. His students run their tailor-made code on MASSIVE supercomputers saving time and money.

Premaratne’s group, together with Jet Propulsion Laboratory at Caltech, and Georgia State University and the Institute of Optics at the University of Rochester, New York, has modelled and patented the world’s first spaser made completely of carbon. Compared to other heavy metal-based spasers, carbon-based spasers are biocompatible and have, therefore, a high potential for medical applications. 

For example, scientists have already found ways to deliver graphene and carbon nanotubes into cancer cells. By applying highly concentrated coherent fields generated through the spasing phenomena, individual cancer cells can be destroyed without harming surrounding healthy cells.

With the help of the MASSIVE platform, the team has invented several types of spasers, with some even powered by electrical sources. “Almost all the designs except ours are optically powered. That means a laser is needed to get those spasers working,” says Premaratne. But lasers are large compared to spasers and the overall setup is huge even though spases operate in the nanoscale. 

“This is a limitation if we want to use spasers in lab-on-a-chip type scenario,” he says. “Electrically powered spasers, such as ours, can be powered by the current integrated chip technology. So, they are truly nanoscale devices.” 

Premaratne says the field is now matured enough for optoelectronic devices as small as a few hundred nanometers to be a reality.

“About a decade ago, this technology was inconceivable. Now, it’s not science fiction anymore’” says Premaratne, “it can actually be done.”