Detection of microplastic samples based on spatial heterodyne microscopic differential Raman spectroscopy

Abstract As a new global pollutant, microplastics have been widely a concern in recent years. The traditional microplastic detection technology has the disadvantages of weak signal, high cost, and complicated operation. Therefore, this paper designs and builds a set of spatial heterodyne microscopic differential Raman spectroscopy (SHMDRS) system for microplastic detection. The system combines the spatial heterodyne system (SHS) with the microscopic differential Raman system (MDRS). The system was simulated and designed by ZEMAX software, and the SHMDRS system was built on the experimental platform. The 531.742‐ and 532.567‐nm dual‐wavelength lasers were used as the excitation light source. Four kinds of microplastic samples, namely, PS, PC, PP, and HDPE, were tested to verify the feasibility of the system. Under the integration time of 10 s and the laser power of 200 mW, the microplastic samples were detected by the SHMDRS system and dispersive spectrometer, respectively. The signal‐to‐noise ratio (SNR) of Raman spectra of different systems was compared and calculated. The differential Raman spectra of four kinds of microplastic samples were obtained by dual‐wavelength laser, and the pure Raman spectra of four kinds of microplastic samples were restored by multiple constrained iterative algorithm. The results show that the spectral resolution of the SHMDRS system is 2.809 cm −1 , and the spectral range is 255.47–2023.21 cm −1 . The SNRs of the Raman spectra obtained by the SHMDRS system are better than those of the dispersive spectrometer, and the differential Raman spectroscopy can effectively remove the interference of the fluorescence background. This method has a good development prospect.