Fig. 1. Workflow of incidence angle scanning SPRM. (a) Performing the incidence angle scanning. (b) Recording a series of intensity images at different incidence angles. (c) Resonance angle extraction with designed data processing procedure. (d) Reconstructing the sample image with full morphology and high contrast.

Fig. 2. Experimental setup of incidence angle scanning SPRM. NL: negative lens; CL: collimation lens; FL: focusing lens; HWP: half-wave plate; BS: beam splitter; MO: microscope objective; TL: tube lens; BFP: back focal plane. Inset on the left side shows details of the Kretschmann configuration and incidence angle scanning mechanism.

Fig. 3. Data processing procedure of incidence angle scanning SPRM.

Fig. 4. Experiment results of photoresist square sample with side length of (a) 15 μm and (b) 8 μm. Insets are: (a₁), (b₁) SPR; (a₂), (b₂) CRA; and (a₃), (b₃) bright-field image. In (a₁), (b₁), the incidence angle was set as the resonance angle of the background region. (a₄), (b₄) Line-cut profiles along the x, y directions of the SPR and CRA images. The dashed lines of (a₁), (a₂), (b₁), and (b₂) mark the locations of the line-cuts. The red arrow in (a₁) indicates the SPW propagation direction and is applicable to (b₁). The color bar of the SPR image indicates normalized intensity and the CRA image indicates the resonance angle. The scale bar in (a₁) is 10 μm and applicable to (a₂), (a₃). The scale bar in (b₁) is 5 μm and applicable to (b₂), (b₃).

Fig. 5. The CNRs of the SPR images and the CRA images for the photoresist square samples with different side lengths. The insets are the CRA images and SPR images of the photoresist square samples with different side lengths while the scale bar is 5 μm.

Fig. 6. Experiment results of ReS2 2D materials. (a) Bright-field image. (b) SPR image. Color bar indicates gray values. The incidence angle was set as the resonance angle of the background region. (c) RA image. Color bar indicates the resonance angle. The inset of (a) is the corresponding AFM image. Scale bar in (a) is 5 μm and applicable to (b), (c). The red arrow in (b) indicates the SPW propagation direction. (d) The AFM profiles of the thickness along the white dashed cross-section lines in the inset of (a). (e) Cross-section line 1 (2)-cut profiles of the SPR and RA images. Dashed lines of (b), (c) mark the locations of the line-cuts. (f) CNRs of SPR images and RA images for ReS2 2D materials with different shapes. Insets are the RA images and SPR images for the corresponding samples. Scale bar is 10 μm.

Fig. 7. Relationship between the incidence angle θ and angular resolution Δθ.

Fig. 8. Detection limit of the refractive index variation corresponding to the angular resolution of the experimental system.

Fig. 9. The experiment results of the photoresist square sample with a side length of 15 μm. (a₁)–(a₆) Resonance angle image reconstructed by using the data collected with 10, 20, 30, 40, 50, and 60 μm stepping intervals of the linear translation stage. The color bar indicates the resonance angle and is applicable to (a₁)–(a₆). The scale bar in (a₁) is 5 μm and applicable to (a₂)–(a₆). (b₁)–(b₆) The scanning points in the reflectance curves of the sample and background. The number of scanning points for (b₁)–(b₆) is 71, 36, 24, 18, 15, and 12, respectively.

Fig. 10. The CNRs of the resonance angle images for the 15 μm photoresist square sample with different stepping intervals of the linear translation stage.