Chinese scientists are approaching laser propulsion for super-fast, silent submarines

This science fiction-like technology – called “underwater fiber laser-induced plasma detonation wave propulsion” – could have “broad applications in areas such as stealth propulsion for submarines,” they said.

The project team is led by Ge Yang, associate professor at the school of mechanical and electronic engineering at Harbin Engineering University in Heilongjiang province, where China’s first submarine was developed.

The leap in technological advancement of the PLA Navy’s weapons and equipment in recent years is closely linked to this huge institute, located in the heavy industrial production center of northeastern China.

The US government has imposed strict sanctions and blockades on the university’s more than 30,000 students and scientists.

According to a peer-reviewed paper by Ge’s team, published last month in the Chinese academic journal Acta Optica Sinica, the technology pulses a large number of powerful laser beams from different angles around the submarine.

“This method can also be applied to underwater weapons, creating a phenomenon of supercavitation, which significantly increases the underwater range of projectiles, underwater missiles or torpedoes,” Ge and his colleagues said.

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The possibility of underwater laser propulsion was first proposed by Japanese scientists twenty years ago. The idea is to use lasers to generate plasma in water and then use the detonation wave, formed by plasma expansion, for propulsion.

Little progress was made because the scientists found it impossible to generate a driving force in a specific direction, due to the way the detonation wave spreads from one point in all directions.

A number of countries, including China, funded extensive follow-up research, with one promising approach involving applying the force of the detonation wave to small spherical particles made of metal or other materials.

When these particles, also called working media, move at high speed in a specific direction, they exert an opposite force on the submarine according to Newton’s law.

However, all efforts to date have resulted in very low efficiency, with 1 watt of laser power generating only one millionth of a newton of thrust, which has no practical application value.

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Ge and his team said they solved the problem by designing a laser engine that improves the efficiency of converting lasers into thrust by three to four orders of magnitude.

Contrary to the global research community’s common view that adding restrictive devices would cause significant energy loss, the Chinese scientists added a device resembling a gun barrel to the ends of the fibers.

According to the article, the researchers solved the problem of energy loss by modifying the shape and internal structure of the barrel, smoothing the barrel-fiber interface into a U-shape.

They also used a pair of barrels to bombard the working medium particles and added carefully designed protruding structures within the barrel to reduce the interaction and internal friction between shock waves, the paper said.

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Within the Chinese military

Within the Chinese military

Some of the technologies behind the breakthrough had their origins in aerospace defense, where China has developed advanced plasma-electric propulsion engines as part of its significant investments in hypersonic weapons research.

According to the article, this area of ​​research, which involves the physical mechanisms of detonation shock waves and propulsion media, has provided valuable insights for the design and manufacturing of underwater laser propellers.

Although a nuclear reactor on a submarine generates more than 150 megawatts of thermal power – enough for the laser propulsion system – many challenges still need to be overcome before the technology can be applied to nuclear submarines, the team said.

These include heat dissipation from the optical fibers, durability in high-power, high-salinity environments, as well as matching optical fiber emission windows to the submarine’s anechoic surface tiles.

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The technology would also require significant changes in submarine control and surface control methods, according to the article.

The researchers say that despite these challenges, this disruptive technology aligns with the current global shift from mechanical transmission to purely electric propulsion in the new industrial revolution.

In addition to potential military applications, underwater laser propulsion could also be applied to improve the efficiency of civilian ships and achieve “green shipping,” Ge’s team said.