Fig. 3: Polarization-free THz image.

2D Fourier transform of Fig. 2b (a) and 2c (b). The amplitude |F(u_x, u_y)| (|F(u_x, 0)| and |F(0, u_y)| are in red circles and blue dots, respectively) is shown as a function of the spatial frequency (upper panels). log[|F(u_x, 0)|/|F(0, u_y)|] is shown in the lower panels for comparison of the horizontal and vertical spatial distributions. c Assessments (total variation and spatial gradient; see Supplementary section 7 for details) of the fused image as a function of weight fraction r. The blue open circle indicates the minimum TV = 7.59 obtained at r = 0.53. d Fused polarization-free THz image with optimized SNR = 15.31 at r = 0.53.