Tiny ‘metajets’ could use light to steer sails for interstellar travel

The prospect of interstellar travel using light propulsion has moved a step closer to reality. Light sails, expansive sheets propelled by light reflecting off them, represent a promising approach to traversing vast cosmic distances. Now, there may be a solution for steering these sails.

“We already knew that light or lasers could transfer momentum, but now we can also direct it,” states Kaushik Kudtarkar from Texas A&M University. He and his team have developed a compact device named a metajet, which leverages light refraction, not merely reflection, to move in multiple directions simultaneously.

This device consists of a metasurface, an ultra-thin sheet designed to control light. In an innovative twist, the researchers used light to control the metasurface. Microscopic pillars on the material guide the light, with their size and arrangement determining the momentum’s intensity and direction imparted on the device, which measures approximately 0.01 millimeters in width.

In testing, the team submerged the silicon device in water and directed a laser at it, using a microscope to observe its movement. The metajet demonstrated both levitation and horizontal movement, achieving a top speed of around 0.07 millimeters per second.

“Having understood the forces acting on this device, we can modify the metasurface design to steer it as desired,” Kudtarkar explains. He mentions that metasurfaces capable of changing shape over time could be applied to light sails for spatial navigation.

“While space applications are possible, these devices can also be scaled for biomedical use,” Kudtarkar adds. They could help direct drugs to specific areas without exposing them to laser heat, which can harm molecules. Metajets enable this by shielding the drugs from direct laser exposure.

Currently, the researchers aim to adapt their device for use with various light wavelengths, particularly sunlight’s broad spectrum, to enhance compatibility with light sails designed for space exploration. “It’s somewhat futuristic,” Kudtarkar remarks.