Polychromatic speckle mitigation at surface discontinuities

Speckle mitigation via polychromatic illumination is used for many applications, including remote sensing, active target tracking, and optical tomography. However, the impacts of target surface discontinuities on polychromatic speckle mitigation have not been studied in the past. This work investigates such impacts by using polychromatic wave-optics simulation of the imaging of a cutoff-cone target and other complex shapes. It compares results from the depth-slicing, spectral-slicing, and full-time methods for polychromatic wave-optics simulation. The results show that points of discontinuity cause changes in speckle mitigation, and these changes occur over distances on the order of the diffraction limit. Because of the high degree of accuracy of the full-time method, its results are taken as truth. The other methods are numerically efficient, but less accurate. A comparison of the results from those methods to the truth data shows that the spectral-slicing method is accurate about points of discontinuity. On the other hand, the depth-slicing method is a bit inaccurate in some cases. Ultimately, the results indicate that one needs to properly model the transitions in speckle mitigation caused by surface discontinuities to create accurate speckle images. Further, such transitions are captured correctly by both the full-time and spectral-slicing wave-optics methods.