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J. Eur. Opt. Society-Rapid Publ. 22, 21( 2026)
Figure
3. Evolution of R2-C4 indentation( HV0.5): microscopic dark field images( grey scale) and WLI measurements( false color) are compared for selected PJE steps with etching depths of d.( A) Indentation prior to PJE and( B)–( D) after PJE steps # 5 and # 6.
Figure
4. 3D representations of OCT measurements of the R2-C4 indentation( HV0.5):( A) initial state,( B) after PJE step # 3, and( C) after PJE step # 5.
cone-shaped cracks generated by Vickers indentation in fused silica generally exhibit the greatest subsurface depth. OCT-based 3D imaging results confirm this behavior, revealing that cone cracks coincide with the deepest SSD induced by Vickers indentation in fused silica, where the SSD exhibits a ring-like distribution, as illustrated in Figures 4B and 4C. The measured SSD 99. 9 values in the initial state, after PJE # 3, and after PJE # 5 – including the PJE removal depth as determined by OCT – were 32.6 lm, 34.7 lm, and 34.1 lm, respectively. Based on these measurements, the greatest penetration depth of the cone crack at indentation R2-C4 is estimated to be approximately 33.8 lm, representing the average of the three values.
A similar picture is obtained when looking at the R19- C7 indentation. The most extensive etching steps were achieved in row 19( see Fig. 1). Thus, in dark field microscopy presented in Figure 5, the expansion along the cone crack can already be seen after a removal of 27.0 lm. The result is interpreted as preferential and hence anisotropic etching of the morphologically distorted surface, while isotropic etching is assumed for bulk material. The latter takes place in the subsequent steps, where the indentation increases laterally with increasing etching depth. After an etching depth of approx. 83.3 lm, shown in Figure 5, the inner structure of the indentation can no longer be recognized. In applied DF microscopy, scattered or reflected light is directed obliquely onto the sample surface. This highlights scratches and near-surface damage causing them to appear bright.
3.2 Evolution of SSD and the roughness parameter Sv
All 190 Vickers indentations – measured before PJE, as well as after PJE # 3 and PJE # 5 – were recorded using OCT and evaluated with MATLAB Ò. The evaluation procedure involved preprocessing the OCT signals to reduce noise, followed by segmentation of the indentation profiles. Key parameters such as indentation depth and lateral dimensions were then extracted for quantitative analysis and visualization. The final SSD depth given in Figure 6 considering the removal d of the PJE was calculated by
SSD ½ lmŠ ¼ SSD 99: 9 þ d: ð3Þ
As an example of the OCT analysis, Vickers indentation R2-C4 is presented in Figure 7. The color-coded depth maps as top views on the sample indicate the local SSD depths