Image of the single-photon Raman lidar system. Mingjia Shangguan et al/Xiamen University
A team of Chinese researchers from Xiamen University has won the 2023 “Best Paper Prize” from Applied Optics for their groundbreaking work on a single-photon Raman lidar system. Published in June last year, their paper outshone 1,278 other submissions, securing the top spot.
The paper presented radar technology capable of detecting objects at significant depths with such clarity that it has been compared to “fishing for a needle in the sea.”
This new technology is highly sensitive and uses a low-noise single-photon detector and could prove very useful for various underwater sensing activities like ocean surveys, oil spill detection, and deep-sea resource exploration.
The device stands out because of its relatively small size, very low power consumption, and ability to operate at depths up to 3,280 feet (1,000 meters) below sea level. The team reported in 2023 that it is so sensitive that it can analyze the thickness of oil spills up to 39.4 feet (12 meters) away using just a 1-microjule laser pulse.
“Differentiating substances in water and detecting their distribution characteristics in the ocean is of great significance for marine monitoring and scientific research,” said research team leader Mingjia Shangguan from Xiamen University in Chinas told Optica back in 2023.
“For instance, the remote sensing of underwater oil that we demonstrated could be useful for monitoring leaks in underwater oil pipelines,” he added.
A different take on lidar at sea
Traditional lidar systems, typically used on ships, aircraft, or satellites, are capable of large-scale ocean profiling. However, their detection depth is limited, particularly in rough sea conditions.
In contrast, Raman lidar systems can analyze underwater environments at various depths without being impacted by these sea conditions. Raman lidar operates by emitting a pulse of green laser light into the water, where it interacts with substances such as oil.
This interaction generates inelastic Raman signals that can be used to identify different substances. By measuring the intensity of these Raman signals at specific wavelengths, lidar can provide information about the oil content in the water.
The new Chinese lidar system measures 15.7 inches (40 cm) in length and has a diameter of 7.87 inches (20 cm), allowing it to function effectively up to a depth of 3,280 feet (1,000 meters) underwater.
To enhance sensitivity, the researchers have integrated single-photon detection into their compact underwater Raman lidar system.
“Mounting an underwater Raman lidar system on an autonomous underwater vehicle or remotely operated vehicle could enable monitoring for leaks in underwater oil pipelines,” Shangguan explained. “It could potentially also be used to explore oceanic resources or be applied in detecting seafloor sediment types, such as coral reefs,” he added.
Many applications for underwater sensing
Since this technology enables high-resolution laser imaging of small underwater targets, it holds potential applications in underwater archaeology, structural inspections, and military areas such as reconnaissance and submarine detection.
In the paper, Shangguan stated that the team’s next plan is to develop an underwater Raman lidar using a shorter-wavelength laser, such as a blue laser, to minimize the influence of chlorophyll fluorescence from marine plants. “Additionally, we will integrate [the system] into autonomous underwater vehicles (AUVs),” he said.
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According to an official report from Xiamen University, the South China Morning Post (SCMP) reports, the team’s radar technology can detect the optical properties of water, water particle profiles, bubbles, water depth, oil spills, and more.
“Such radar systems have already been integrated into Xiamen University’s Jia Geng research vessel, AUVs and drones, playing a key role in marine surveys, deep-sea resource exploration, environmental monitoring, and underwater target imaging and recognition,” it said.
