A new laser-based propulsion technique developed by researchers at the Harbin Engineering University in China could help the People’s Liberation Army (PLA) build silent yet superfast submarines in the future.
The technology could also power underwater missiles and torpedoes, a South China Morning Post (SCMP) report said.
The concept of underwater laser propulsion isn’t new. Japanese researchers first considered it more than twenty years ago. In principle, the technology works fairly simply.
Lasers are used to generate plasma inside water, which is then used to make a detonation wave by plasma expansion. The detonation wave is used to propel a craft or weapon ahead.
The greatest hurdle, though, was the application. Since detonation waves spread from a single point to all directions, scientists found it impossible to get the detonation wave to generate a force in a specific direction. This meant little progress was made on this concept until the Chinese funded extensive research.
Thrust of a commercial jet engine
A research team led by Ge Yang, a professor at the School of Engineering at Harbin University, has now found a way to improve the efficiency of laser propellers using a coating of optical fibers – also referred to as underwater fiber laser-induced plasma detonation wave propulsion.
Using this approach, the researchers claim to be able to generate 70,000 newtons of thrust using just two megawatts of laser power. The thrust generated is similar to that of a commercial jet engine.
In addition to generating thrust, the laser also vaporizes the seawater close to the vessel, creating bubbles on the submarine’s surface and reducing water resistance. This phenomenon, known as supercavitation, could potentially allow submarines to travel at supersonic speeds underwater.
More importantly, since the propulsion system is not mechanized, the submarine will not generate any noise, adding to its stealth.
Research drawing US ire
To solve the problem of the detonation wave, researchers have previously proposed using working media—tiny spherical particles that travel at a high speed in one direction and, per Newton’s laws, exert an opposing force on the submarine, propelling it.
Experiments attempted using working media and a one-watt laser generated only a small fraction of thrust than expected and were ineffective as a propulsion method. However, the laser engine designed by Ge’s team improved the output by up to four orders of magnitude.
The researchers used a device that resembled a gun barrel and adjusted its shape and internal structure to minimize the energy loss associated with the use of constraining devices.
The SCMP report added that a pair of such barrels were used to bombard the working medium particles. The protruding structures inside them reduced internal friction between shock waves.
A nuclear reactor on a submarine generates 150 MW of power, which is sufficient to power such a laser propulsion system. However, researchers still need to work on other components, such as heat dissipation of optical fibers and durability of the equipment in high salinity environments, before the tech can be transferred to real-world scenarios.
When ready, the same technology could also power a range of underwater projectiles, missiles, and torpedoes.
The recurrent output of high-end research from Harbin University in naval warfare has prompted blockades and sanctions on 30,000 students and staff associated with the educational institution from the US, the SCMP report added.
