Fig. 1. Diagram of confocal Raman microscopy

Fig. 2. The relationship between the lateral FWHM and the defocusing amount u

Fig. 3. (a) Influence of axial scanning pitch on RMSE at different spherical aberration; (b) Influence of axial scanning pitch on RMSE at different astigmatism; (c) Influence of axial scanning pitch on RMSE at different SNR

Fig. 4. Actual axial response curve and focusing result of BFSCRM
C_I is the actual curve; l_L and l_R are fitting lines; l_D is difference line; z_f=199.695 μm is the focus position

Fig. 5. Focusing repetition accuracy of BFSCRM

Fig. 6. (a) microscopic observation image; (b) zoom-in the area shown in red area of (a); (c) Raman spectrum of point A in (a)

Fig. 7. Raman images of a vertical bar with a 5 μm period
(a): Without auto-focusing; (b): Using BFSCRM