Caltech’s pioneering research in laser-driven lightsails could revolutionize interstellar travel. Scientists are developing ultrathin sails capable of propelling spacecraft to distant star systems at unprecedented speeds using laser power. This groundbreaking work brings the concept of lightsail propulsion out of science fiction and into the realm of possibility.
In 2016, the Breakthrough Starshot Initiative, led by physicist Stephen Hawking and entrepreneur Yuri Milner, launched a program to study laser-powered lightsails. The ultimate goal is to send tiny space probes to Alpha Centauri, the nearest star system to our own.
Testing Ultrathin Membranes
Professor Harry A. Atwater and his team at Caltech have created a platform to study ultrathin membranes suitable for lightsails. Their experiments measure the force lasers exert on the sails, marking a significant step from theoretical concepts to practical observations.
“Developing a membrane that can withstand heat and maintain its shape under pressure is crucial for lightsail propulsion,” explains Atwater. “By understanding how materials respond to radiation pressure, we can progress towards building stable and high-speed space probes.”
A Major Leap Forward
The research, published January 30 in Nature Photonics, involves postdoctoral scholar Lior Michaeli and graduate student Ramon Gao. Their work introduces a novel method to measure the forces acting on a lightsail, overcoming challenges posed by laser heating.
Engineering Nanoscale Solutions
At Caltech’s Kavli Nanoscience Institute, the team fabricated a microscopic “trampoline” using electron beam lithography. This tiny sail, made of silicon nitride and only 50 nanometers thick, was suspended by delicate springs and subjected to laser light.
By studying the trampoline’s vibrations, Michaeli and Gao devised a method to measure radiation pressure without interference from heat. Their approach also enabled them to measure laser power, providing dual functionality from a single instrument.
A Precision Measurement Breakthrough
The team built a common-path interferometer, a device that amplifies small movements by comparing laser beams on identical paths, eliminating noise. This setup allowed the researchers to detect tiny motions as small as picometers—trillionths of a meter—as well as the sail’s stiffness.
“Our platform is unique in its ability to measure optical forces and torques, crucial for controlling a freely moving lightsail,” explains Ramon Gao. This capability is essential for the future of interstellar propulsion.
Reproducing Space Conditions
To simulate real spaceflight, the researchers angled the laser beam to study its impact at different angles. They calibrated these measurements using the sail’s own power readings, identifying factors such as beam diffraction affecting force.
Future Directions
The Caltech scientists plan to utilize nanoscience to control the side-to-side motion and rotation of lightsails. Their goal is to develop surfaces that can stabilize a sail, ensuring it remains on course through the laser beam.
“By imparting restoring forces or torque to the sail, we can maintain its orientation, even under disturbances,” says Michaeli. “This is a critical step in advancing the feasibility of lightsail propulsion systems.”
Conclusion
Caltech’s innovative research in laser-driven lightsail propulsion signifies a major step towards interstellar travel. By overcoming obstacles related to material science and measurement techniques, the team is bringing sci-fi concepts into practical application.
“This is not only about reaching distant stars,” emphasizes Gao. “It’s about humanity’s quest for discovery and expansion into the cosmos.”
Reference and Support
The study, titled “Direct radiation pressure measurements for lightsail membranes,” was published in Nature Photonics on January 30, 2025. The research was supported by the Air Force Office of Scientific Research and the Breakthrough Starshot Initiative.
Contributing authors to the paper include Harry A. Atwater, Lior Michaeli, Ramon Gao, Michael D. Kelzenberg, Claudio U. Hail, Adrien Merkt, John E. Sader, and others.
DOI: 10.1038/s41566-024-01605-w
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