"Plastic pollution poses a serious threat to marine ecosystems and human livelihoods, affecting industries like fisheries, tourism, and shipping," explained Toshihiro Somekawa, research team leader from the Institute for Laser Technology in Japan. "To manage and protect the marine environment, it's essential to assess the size, concentration, and distribution of plastic debris. However, traditional lab-based methods are time-consuming, labor-intensive, and costly."

Detailed in the journal Optics Letters by the Optica Publishing Group, the compact and energy-efficient system is optimized for drone-based applications. It demonstrated the ability to identify plastics up to six meters away, with a wide imaging field of 1 mm x 150 mm.

"A drone equipped with our lidar sensor could be used to assess marine plastic debris on land or in the sea, paving the way for more targeted cleanup and prevention efforts," added Somekawa. "The system could also have broader applications, including detecting hazardous gas leaks."

To address these challenges, the researchers combined lidar-based distance measurement with hyperspectral Raman spectroscopy, developing a prototype system equipped with a 532-nm green laser and a 2D imaging spectrometer featuring a gated intensified CCD (ICCD). This design enabled the detection of Raman signals backscattered from distant targets, achieving hyperspectral imaging with precise range resolution.

"By integrating imaging and spectroscopic measurements, we could leverage the unique Raman spectrum of each plastic type to map the spatial distribution of plastic debris," said Somekawa. "The system allows hyperspectral information to be obtained at various distances, thanks to the pulsed laser enabling range-resolved measurements."

Next steps include adapting the technology to monitor microplastics in aquatic environments. The 532-nm laser's ability to transmit effectively through water opens the door for enhanced detection of submerged and floating microplastics.