04 Jul 2023
Xiamen University device could also detect sediment types and explore oceanic resources.
A project at China's Xiamen University has now reported a new single-photon Raman lidar system that operates underwater and can remotely distinguish oil and other substances, detecting them from several meters away.
Published in Applied Optics, the team's work could offer a route to more compact and energy efficient lidar platforms for use in the demanding undersea environment.
"Traditional Raman lidar systems rely on increasing laser power and telescope aperture to achieve remote sensing detection, which leads to a large system size and high-power consumption that make it difficult to integrate lidar systems onto underwater vehicles," said Mingjia Shangguan from Xiamen University.
"The use of single-photon detection technology made this work possible."
Exploiting advances in photon sensing as a route to more versatile marine lidar platforms has been a topic of research for some time. Traditional lidar systems have limited detection depth, especially during rough seas; but Raman lidar, detecting both elastically backscattered light and the Raman signals of specific molecules, can be used at different depths while being less affected by sea conditions.
In May 2023 Heriot-Watt University reported an alternative lidar device hinging on picosecond resolution time-correlated single-photon counting, said to be suitable for underwater use thanks to the enhanced sensitivity the architecture allows.
Detection of oil from 12 meters away
The Xiamen device measures 40 centimeters long with a diameter of 20 centimeters, and could potentially withstand operational conditions up to 1 kilometer underwater according to the project team. In demonstrations the new lidar system was used to detect varying thicknesses of gasoline oil in a quartz cell positioned several meters away from the system.
Both the lidar system and the quartz cell were submerged at a depth of 0.6 meters underwater in a large pool. In these proof-of-concept trials, the lidar system was able to detect and distinguish thicknesses of gasoline ranging from 1 to 15 millimeters.
"Due to the single-photon sensitivity, the detection of the relatively weak Raman backscattered signal from underwater oil was realized with a laser with a pulse energy of 1 micro-Joule and a telescope with a diameter of 22.4 millimeters," noted the project in its Applied Optics paper. "An experimental demonstration was conducted to obtain the distance-resolved Raman backscatter of underwater oil of different thicknesses up to a distance of 12 meters."
The researchers are now working to increase the number of detection channels and the Raman spectral resolution of the single-photon lidar system, to enhance its ability to distinguish different substances in water. This would allow it to be used to analyze types of underwater bubble as well as for detection of corals and manganese nodules, according to the project.