Fig. 1. The schematic of CARS process

Fig. 2. Algorithmic framework

Fig. 3. Raman spectrum of polystyrene at different concentrations

Fig. 4. Multi-channel imaging of polystyrene centered at 1 597 cm^-1
(a): The white light imaging; (b): The CARS imaging

Fig. 5. Multi-channel imaging of polystyrene centered at 1 597 cm^-1 in seawater
(a): The white light imaging; (b): The CARS imaging

Fig. 6. CARS imaging signal of polystyrene in seawater under different exposure times
(a): Exposure time: 2 μs·pixel^-1; (b): Exposure time: 8 μs·pixel^-1

Fig. 7. CARS imaging of polystyrene in seawater under continuous scanning

Fig. 8. Raman spectrum of different sand

Fig. 9. Multi-channel imaging of sand
(a), (b) are white light and CARS images of transparent sand particles; (c), (d) are white light and CARS images of dark sand particles

Fig. 10. Raman spectrum of different locations in sand containing polystyrene

Fig. 11. Raman spectrum of polystyrene in sand

Fig. 12. CARS imaging of polystyrene in sand centered at 1 597 cm^-1

Fig. 13. CARS imaging of polystyrene in sand after processing by algorithm
(a): Median filter; (b): Erode and dilation; (c): Corrosion and expansion combined with median filtering