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熔石英亚表面划痕对入射激光的近场调制是导致光学元件低阈值损伤的主要因素之一.用三维时域有限差分方法研究了连续横向划痕的近场分布,对比了尖锐截面与光滑截面场调制的差异,着重探讨了光场调制与划痕宽深比R的关系.研究表明:酸蚀后的光滑截面有助于减弱近场调制,这类划痕的R>10.0时调制较弱且相互接近,R<5.0时调制显著增强.当R取1—3时,亚表面的调制达最大值,最大电场幅值为入射波幅值的4.3倍.当R取1.0—3.5时,缺陷附近有80%以上取样点的最大电场幅值超过入射波幅值的2倍.随着深度的增大,强场区具有明显的“趋肤效应”:位于划痕正下方的强场区首先往左右两侧移动,然后移向抛物口界面以及水平界面,同时衍生出的多条增强线诱导整个亚表面层的光场增强.
Near-field modulation of the sub-surface scratches on the incident laser is one of the main factors leading to the low threshold damage of optical components. The three-dimensional finite difference time domain method is used to study the near-field distribution of continuous transverse scratches, The relationship between the modulation of light field and the width-to-depth ratio of scratches is emphatically discussed. The results show that the smooth section after acid etching helps to attenuate the near-field modulation. When R> 10.0, the modulation of these scratches Weak and close to each other, R <5.0 modulation was significantly enhanced.When R take 1-3, sub-surface modulation up to the maximum amplitude of 4.3 times the amplitude of the incident wave.When R take 1.0-3.5, More than 80% of the sampling points near the defect have a maximum electric field amplitude more than twice the amplitude of the incident wave. With increasing depth, the strong field region has obvious “skin effect”: the strong electric field just below the scratches The field first moves to the left and right, and then moves to the parabolic interface and the horizontal interface. At the same time, the derived multiple enhanced lines induce the enhancement of the light field of the entire subsurface layer.