Take a smidgen of hydrogen, then blast it with lasers to set off a small thermonuclear explosion. Do it right, and maybe you can solve the world’s energy needs.

A small group of start-ups have embarked on this quest, pursuing their own variations on this theme — different lasers, different techniques to set off the fusion reactions, different elements to fuse together.

“There has been rapid growth,” said Andrew Holland, chief executive of the Fusion Industry Association, a trade group lobbying for policies to speed the development of fusion.

Private enterprise promises quick innovation, but it was a breakthrough achieved by a big, costly and ponderous government-run project that spurred this wave of attention to laser fusion.

In December last year, after years of trying, the National Ignition Facility, or NIF, at Lawrence Livermore National Laboratory reported that it had finally lived up to its middle name: ignition. For the first time anywhere, a laser-induced burst of fusion produced more energy than that supplied by the incoming lasers.

“We’re really excited by the NIF results,” said Kramer Akli, who manages the fusion energy sciences program at the United States Department of Energy.

A decade ago, a report by the National Academy of Sciences found much to like in the energy potential of laser fusion but recommended that the United States hold off major investments until ignition was achieved.

That time is now.⚛️⚡️🔌

The sun generates heat and light by jamming — fusing — hydrogen atoms together into helium. Harnessing that phenomenon on Earth could lead to a bountiful energy source that does not generate planet-warming carbon dioxide or long-lived radioactive waste.

For more than 70 years, fusion research has largely focused on mimicking the inside of the sun in reactors known as tokamaks, which trap superhot hydrogen gas within strong magnetic fields so that atoms will collide and fuse.

NIF offered another possibility. It was designed primarily to help verify computer simulations of nuclear explosions after a treaty banned tests of actual exploding nuclear weapons. But a secondary aim of NIF was to explore the possibility that technology could be adapted to provide a bountiful, clean source of energy.

Until two years ago, NIF sputtered well short of its goals. But in December 2022, a burst finally crossed the threshold of ignition.

“Simply put, this is one of the most impressive scientific feats of the 21st century,” Jennifer M. Granholm, the U.S. secretary of energy, said during a celebratory news conference announcing the success.

In July this year, Livermore repeated the feat, generating even more energy.

The researchers at Livermore are joined by scientists at other institutions, like the Naval Research Laboratory in Washington and the Laboratory for Laser Energetics at the University of Rochester in New York. While the lasers at those institutions are not powerful enough to create fusion, they allow scientists to investigate some of the basic science and tweak their concepts on a smaller scale.

“There’s still a lot of foundational science and technology to be done,” said Dr. Akli of the Energy Department, but he added that he currently did not see any showstopping obstacles.

“We are not predicting the timeline, but I’m really very optimistic,” he said.⚛️⚡️🔌

Private enterprise is jumping in too, and scientists are following.

Debra Callahan worked on NIF at Livermore for more than 20 years. An experiment she contributed to in August 2021 represented a major advance. Although it still fell short of ignition, the amount of fusion energy released leaped upward, and it was clear that the explosion had generated torrents of particles that heated the surrounding hydrogen, setting off cascades of additional fusion reactions.

To celebrate, Dr. Callahan got a tattoo inked on her left forearm: a drawing of the sun with an infinity sign inside.

She also left Livermore. Today, Dr. Callahan is a senior scientist at Focused Energy Inc., one of the start-up laser fusion companies.

“For me, that’s the next grand challenge — to try to make fusion energy,” she said. “I’d like to see more clean energy for my daughter and her future children.”