Fig. 3

Epi-detected PESRS. a A schematic of epi-detected PESRS. A polarizing beam splitter (PBS) and a quarter wave plate (QWP) changes the polarization of incoming and backscattered lasers by 90°. In this way, the stimulated Raman loss signal passes the filter and is detected by a photodiode (PD). b Raw PESRS image of adenine adsorbed on Au NPs-SiO₂ substrate. The color of each pixel represents the average intensity of each PESRS spectrum. c Denoised PESRS image of adenine adsorbed on Au NPs-SiO₂ substrate. The color of each pixel represents the intensity of the 733 cm⁻¹ peak in each denoised and background-corrected PESRS spectrum. The image area is 30 μm × 30 μm. d Single-pixel spectra of adenine on the Au NPs-covered SiO₂ substrate obtained from spot 1 and 2 indicated in c.