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.