RamaCam: Autonomous in-situ monitoring system of marine particles by combining holography and Raman spectroscopy

Suspended particles in the ocean play an important role in global nutrient cycles. In this paper, a novel technique for the non-contact fast identification of marine particles is reported. An integrated method of digital holography and Raman spectroscopy aiming at in-situ continuous monitoring of marine particles, particularly in the deep sea where the density of particles is extremely low, is proposed. A particle located in a 20 cm water channel was illuminated using a collimated continuous wave laser beam which is used to take both a hologram and Raman spectrum to identify the shape, size and composition of the suspended material. Using a compact system, we have demonstrated the morphological and chemical analysis of plastic particles in a large volume of water. Furthermore, we have developed the in-situ device and tested it in the deep sea at a water depth of 900 m for the first time. The technique will contribute to the understanding of global-scale marine particle distributions.