Defect edge steepness dependence of multiple nonlinear hot-image formation from a single phase defect.

ABSTRACT

Nonlinear hot image is one of the key elements that limit the output performance of high-power laser systems. In most hot-image researches, only one hot image peak is observed in the conjugate position for a single defect. Generally, multiple hot image peaks occur for multiple defects or cascaded nonlinear media. However, a new phenomenon is found by numerical simulation in our work one defect can also afford two hot-image peaks near the conjugate position when considering the defect edge steepness. The super-Gaussian defect model is employed to mimic the defect edge steepness. When the super-Gaussian order is higher than one, there could be two hot image peaks under certain conditions. The formation of the double hot image peaks is primarily due to the co-effect of the hard-edge diffraction and the self-focusing effect. The influence of different factors, including the super-Gaussian order, defect size, modulation depth, and Kerr medium thickness, on the double hot image peaks intensity and location is systematically investigated. The results show that with the increase in the super-Gaussian order, the intensity of the double hot image peaks increases gradually. The defect size has a great influence on the position of the two hot image peaks. The modulation depth and thickness of the Kerr medium influence the intensity of the two hot image peaks; however, they have less impact on the peak location. Importantly, the defect edge steepness and size dependences of multiple nonlinear hot-image formation from a single-phase defect are further discussed in this paper. The two hot image peaks are fatal to optical components in high-power laser systems; in particular, the hot image peak behind the conjugate position is totally unexpected for a single defect. This research provides insights into basic physical images and hot-image formation laws. It also provides important guidance for optical defect specification evaluation and optical component layout design, as well as for beam quality control, in high-power laser systems.