Non-conjugate multi-peak hot-images induced by double defects in high power laser systems

Abstract

In high-power laser systems, hot image is a phenomenon of drastic intensification on the downstream light field due to nonlinear Kerr self-focusing, which poses a threat to the safety of optical components. It is traditionally believed that a single defect will trigger a hot image, which appears at the downstream conjugate position of the defect relative to the nonlinear medium. Our previous study has shown that a phase defect can cause double-peak hot images when considering the defect edge steepness. When the number of defects increases, the downstream modulation becomes more complex. Here the evolution of the hot-image is analyzed when there are two symmetrical distributed super-Gaussian defects around the beam center for example. The results show that double defects will form five modulation peaks. The second and fourth peaks are the results of two single defects. Another three peaks are in the center of the beam, which do not appear in the case of single defect. The linear modulation peak is generated by the interaction of diffraction fringes from double defects and finally forms the first peak. The second and third strong peaks are caused by the interference between the second and fourth peaks, respectively. The characteristics of these three peaks are affected by the center spacing and size. The existence of these new strong modulation regions will pose a potential damage threat to the optical components at this position, so they need to be avoided when designing the arrangement of the components.