Laser-Made Plasma Antenna Transmits Radio Waves From Thin Air

The laser alone does not transmit anything. The team, led by Pryia Darshni, had to feed radio-frequency energy into the channel without disturbing it, and an ordinary wire could have damaged the delicate structure. The researchers instead placed a metal ring around the laser beam. It works as a capacitive coupling, allowing a radio generator to act on the plasma electrons without direct contact.

The length and direction of the antenna can be changed by adjusting the beam. Antenna geometry affects its characteristics and frequency range, and conventional designs may need mechanical changes for similar tuning. Here, in theory, laser control would be enough.

Limits of the experiment

The test used 30 MHz, which corresponds to a wavelength of about 10 metres. The received signal was 2.5 times stronger than in a setup where the laser did not create plasma. However, the receiving antenna sat only about 5 centimetres from the transmitter, so this was a near-field measurement, not long-range communication. The team also did not show that the plasma antenna can receive signals, though they see no fundamental obstacle.

Space use remains the open question. According to co-author Paul Franzon, low Earth orbit holds enough thin gas to form plasma. But the density is far lower than in a lab, which changes how the gas ionizes and how a channel can be sustained. The laser, its electronics, power source and control system also need energy, and without data on radiation efficiency and energy cost it is unclear whether the design would cut satellite mass.

Before plasma antennas could compete with metal ones, researchers must show transmission over longer distances, operation across frequency bands and stable emission at reasonable power consumption. The results were published in the IEEE Journal of Microwaves.