The image is obtained by correlating the intensity of a reference beam, which does not interact with the object but has its spatial intensity distribution recorded, with the intensity of a test beam that illuminates the object and is measured by a single-pixel detector. This approach offers significant advantages, such as robustness against noise and distortions and enhanced security. The probing patterns used in the reference beam can either be random and captured with a high-resolution detector or pre-programmed for computational correlation imaging. The concept of correlation imaging has recently expanded beyond the spatial domain. We develop correlation imaging techniques across various wavelength regimes in the temporal and spectral domains, with applications in spectroscopy, communication and imaging.
