Near-field terahertz single-pixel imaging with ultralow sampling ratio

In this work, we propose what we believe to be a novel reordered Hadamard basis method, namely frequency-domain modulus-correlation Hadamard (FMH), which ensures uniform increment of spatial frequencies in both two orthogonal directions. Both simulated and experimental results reveal that the FMH can significantly decrease required sampling ratio for reconstructing high-quality images, compared with the Sylvester Hadamard and the Walsh Hadamard. By integrating a pseudo-background post-processing technique, we achieve a remarkably low sampling ratio of 4.27% for terahertz image reconstruction, with the Pearson correlation coefficient exceeding 0.9. This advancement resulted in nearly a 5-fold increase in the acquisition rate of near-field terahertz single-pixel imaging, compared with the Walsh Hadamard.