Laser Beam Sends Electricity Nearly 100 Feet Through the Air

Electricity can be streamed wirelessly across a room through thin air, researchers have found.

Scientists from Seoul, South Korea, have figured out how to transmit 400 milliwatts (mW) of electricity over nearly 100 feet using infrared laser light, according to research published in the journal Optics Express.

"The ability to power devices wirelessly could eliminate the need to carry around power cables for our phones or tablets," research team leader Jinyong Ha from Sejong University in South Korea said in a statement. "It could also power various sensors such as those used for monitoring processes in manufacturing plants."

Four hundred mW is just enough power to charge small sensors but paves the way for larger amounts of power being able to be sent wirelessly across large distances, possibly one day enough to charge mobile phones.

Wireless charging over very small distances has been around for a while and has been commercially available in mobile phones for several years. It works through inductive charging, where a copper coil generates a magnetic field that facilitates the movement of a charge from the charging pad into the phone's battery.

This breakthrough, which was found to work at distances over 98 feet, uses a method called distributed laser charging, which provides "safe high-power illumination with less light loss."

"While most other approaches require the receiving device to be in a special charging cradle or to be stationary, distributed laser charging enables self-alignment without tracking processes as long as the transmitter and receiver are in the line of sight of each other," Ha said. "It also automatically shifts to a safe low power delivery mode if an object or a person blocks the line of sight."

Lasers work by exciting the electrons in the atoms of optical materials like glass, crystal or gas. The lasers use an electrical current or light to such a degree that the electrons move from a lower-energy orbit to a higher-energy orbit around the atom's nucleus, according to Lawrence Livermore National Laboratory's National Ignition Facility.

These excited electrons eventually drop back down in energy, releasing photons of light as they do. These photons are bounced off mirrors back at the optical atoms, creating more and more photons until a powerful beam of many photons is produced. It is powerful enough to pass through the mirrors as a laser beam.

Lasers can be used to transmit a charge between the laser transmitter and a receiver. The distributed laser-charging method enabling long-distance electrical charging separates the transmitter and receiver in the laser-generating system. This system, when in a line of sight, forms a laser cavity in the air between them, allowing the system to deliver light-based power.

This doesn't work if an obstacle blocks the line of sight, however, and the system then switches automatically to a power-safe mode. The laser's wavelength is only 1,550 nanometers, meaning that it's low enough in power to be in the safest part of the infrared spectrum and won't damage human skin or eyes.

One other advantage of this new system is that the receiver, which would be part of the object being charged, measures a mere 0.4 by 0.4 inches, meaning that it could easily be integrated into devices and sensors.

"Using the laser charging system to replace power cords in factories could save on maintenance and replacement costs," Ha said. "This could be particularly useful in harsh environments where electrical connections can cause interference or pose a fire hazard."

Correction 09/05/22, 4:07 a.m. ET: This article was updated to correct a reference to milliwatts in the second paragraph.