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Stephen Chen

Researchers in eastern China say they have developed an airborne laser device that can detect underwater objects at unprecedented depths, technology that one day might be used to track submarines.
The team from the Shanghai Institute of Optics and Fine Mechanics said the device could pick up objects more than 160 metres (525 feet) beneath the sea, twice as deep as devices used today.
“It is the first time [to have reached that depth] … with potential for further improvement,” the institute said on its website.
The airborne laser system was tested over the South China Sea in April and the results were made public this month.

“It provides powerful technical support for satellite laser remote sensing,” the institute said.
The institute is involved in Guanlan, or Sea Watcher, China’s programme to build a laser satellite that can “light up” targets 500 metres beneath the ocean – beyond most submarines’ operational depths.
It is not clear if the April tests were part of the Sea Watcher project.
Will China’s new laser satellite become the ‘Death Star’ for submarines?
Led by Professor Chen Weibiao, the Shanghai team used a beam generated by green and blue lasers. As light – even laser, a pure, coherent form of light – scatters faster in water than in air, the beam must be very powerful to go deep.
Laser devices generate an energised beam of light of a single colour, or frequency. Green and blue beams can penetrate water with relative ease.
Chen’s team also developed a highly sensitive detector that can pick up a single photon reflected from a target, allowing the device to detect bright objects close to the surface as well as targets hidden in the deep, they said.
The researchers did not reveal the location or environment of the experiment, but a photo posted on the institute’s website showed the beam came from a plane flying above clouds. These experiments are typically conducted from a height of 500-1,000 metres (1,600-3,200 feet).

Optical science is becoming a front line in an arms race. Lasers can be used monitor craft that are invisible to sonar, such as submarines with extremely quiet engines fitted with sound absorption materials. They can also help track degaussed submarines with magnetic signatures that are difficult to detect.
Lasers can also detecting waves generated by a moving target, and monitor temperature variations it creates in water.
China is building world’s most powerful laser radar to study Earth’s solar shield
Song Chengtian, associate professor at the Beijing University of Technology who studies laser detection, said the underwater technology had interested the military and researchers for decades.
“Despite tremendous efforts, the depth remains too shallow,” he said.
One reason was that laser devices mounted on planes or satellites were usually compact and their power is limited.
The Shanghai team “may have achieved an important technological breakthrough”, said Song, who was not involved in the study.

According to state media, Chen developed laser equipment for China’s Chang’e 4 lunar exploration programme this year.
“A space-based laser system requires high reliability, high power and high beam quality, but at the same time it must be miniaturised to meet the requirements of the aerospace environment,” he was quoted by Xinhua as saying in August.
Chen could not be reached for comment.


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Science

Chinese scientists develop airborne laser device that could track submarines deep underwater

Researchers from the Shanghai Institute of Optics and Fine Mechanics test their laser detector over the South China Sea. Photo: Chinese Academy of Sciences

epa06262650 The USS Michigan (SSGN 727), the second Ohio-class nuclear-powered guided missile submarine in the US Navy, is docked at naval base in Busan, South Korea, 13 October 2017. The 18,000-ton submarine has a length of 170.6 meters and carries 150 Tomahawk cruise missiles and arrived in South Korea on 13 October amid North Korea's nuclear and missile provocations. EPA-EFE/JEON HEON-KYUN

In this photo provided on Jan. 4, 2019, by China National Space Administration via Xinhua News Agency, Yutu-2, China's lunar rover, leaves wheel marks after leaving the lander that touched down on the surface of the far side of the moon. China's space agency says that all systems are go for its spacecraft and rover that have made a pioneering landing on the far side of the moon. (China National Space Administration/Xinhua News Agency via AP)

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Chinese researchers have developed a sensor that might be able to track submarines. Photo: Handout

The Chinese acoustics research that might help shield submarines from sonar

Submarines now use used a rubber or plastic coating to absorb sound waves produced by sonar. Photo: AFP

Figure 4: The simulated and measured pressure amplitude distributions of one-way edge states. From: Experimental demonstration of anomalous Floquet topological insulator for sound (a,b) The simulated pressure amplitude distributions when pseudo-spin-up and pseudo-spin-down acoustic one-way edge states are selectively excited. We can clearly observe the robustness of the edge states against the sharp bending of the boundaries. (c,d) The measured sound pressure distributions, corresponding to a and b, respectively. The operating frequency of sound is 7.46?kHz. The distance between neighbouring lattice rings is 2D.

Figure 1: Photograph of the fabricated samples. From: Experimental demonstration of anomalous Floquet topological insulator for sound (a) Photograph of a 2D coupled metamaterial ring lattice composed of 3 ? 4 unit cells. The U-shape waveguides are the input and output ports for selectively exciting and extracting edge states with specific pseudo-spins. It is noteworthy that a ring is purposely removed to form a defect, as marked by the red dashed box. (b) Photograph of a unit cell composed of one lattice ring surrounded by four coupling rings with the radius R=77.4?mm. The red arrow shows that the waves in the lattice ring are carrying pseudo-spin-up, viz. propagating in clockwise. (c) Zoom-in photograph of the metamaterial waveguide marked by the black circle in a. The period of the waveguide is P=4.3?mm. The thickness and width of the metal plate is t=1.7?mm and w=17.2?mm.

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Cacs, the world’s first cold atomic clock in space with unprecedented timing accuracy. Credit: Chinese Academy of Sciences

China's Tiangong 2 space lab is launched on a Long March-2F rocket from the Jiuquan Satellite Launch Center in the Gobi Desert, in China's Gansu province, on September 15, 2016. China launched its second space lab on September 15, as the Communist country works towards setting up its own space station. CHINA OUT AFP PHOTO / AFP PHOTO / -

The crew disembarks after taking positions on board for the commissioning of the U.S. Navy attack submarine USS North Dakota (SSN 784) Saturday, Oct. 25, 2014 at the Navy submarine base in Groton, Conn. USS North Dakota is a $2.6 billion attack submarine is capable of launching Tomahawk cruise missiles, delivering special forces and carrying out surveillance over land and sea. (AP Photo/The Day, Sean D. Elliot) MANDATORY CREDIT

Tiangong-2 space lab in ground testing. Credit: Xinhua

Shenzhou XI mission commander Jin Haipeng (left) is a major general in the People’s Liberation Army, while crew member Chen Dong is a colonel. Photo: EPA

News

China


Shanghai team say airborne device can find targets at twice the depth of existing technology



Shanghai team say airborne device can find targets at twice the depth of existing technology.


Technology

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China’s military

China's military weapons