Campus researchers discover energy-efficient way to create nanoscale lasers

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Lawrence Berkeley National Laboratory and UC Berkeley researchers recently discovered a more energy-efficient way to create nanoscale lasers with potential applications for rapidly transmitting large amounts of data in the future.

Nanowire lasers provide a small light source useful in applications such as imaging and data storage, with data traveling faster and farther than in standard electronics. The lasers could potentially improve the speed and quality of data processing in electronics such as phones and computers, according to lead researcher and UC Berkeley chemistry professor Peidong Yang.

In the study, published Feb. 9, the researchers described a new method of growing nanowires using mixtures of chemical solutions.

“One potential application is for communication,” said UC Berkeley postdoctoral student Samuel Eaton, who worked on making the nanowires work as lasers. “Fiber optic cables … run under the ocean from here to Europe, Asia. … Essentially, you can use a laser to send a pulse of light and send information like Morse code.”

Eaton said nanowires are special because their geometry allows them to act as lasers. These tiny lasers are now even more flexible, as researchers can fine-tune their wavelengths by changing the composition of the chemical mixture.

The development simplifies the production of nanowires and increases their stability. While earlier efforts were energy-intensive processes, the researchers’ discovery allows for a more efficient, inexpensive and “green” approach, Yang said.

“(It is) amazing we can use simple solution chemistry to make high quality nanoscale lasers,” Yang said.

The nanowires are made of chemical elements including cesium, lead and iodide or bromide. According to Eaton, the nanowires consist of long “photoluminous” nanocrystals that absorb and release light, depending on certain conditions.

Scientists have found that the crystals grow spontaneously to lengths of 20 to 40 micrometers in a mix of solvent and chemicals, foregoing the high temperatures required in previous methods.

The research group is the first to demonstrate that the material can be used as lasers, according to UC Berkeley graduate student Minliang Lai, who worked on the project.

Lasers from the nanowires are powered by light from a larger laser, which emits light in a beam that is split by a single nanowire crystal to produce its own lasing light, UC Berkeley graduate student Andrew Wong said. Wong said that ideally, the nanowire lasers would be driven by electricity in the future.

Lai said there is still a lot of work to be done before the commercialization of nanowires is possible.

“A lot more work needs to be done in order to make these nanowires able to be excited by electrical injunction or electric pumping,” Wong said.

The most challenging part of the research process was finding the “sweet spot” to make the laser work, Eaton said. Under some conditions, the laser wouldn’t give out light and in other conditions, it would be destroyed.

About 15 years ago, Yang, who has been working on nanostructures for close to 20 years, discovered that a single nanowire can act as a natural lasing cavity, Wong said. This discovery disproved the previous belief that nanowires might be too small — Wong said it “took the science community by storm.”

“It’s sort of an emerging research field,” Yang said. “Before about one year ago, not many people were focusing on this sort of material.”

Staff writer Roann Pao contributed to this report.

Contact Michelle Leung at [email protected] and follow her on Twitter at @michellesleung.