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SEM images of elliptical laser ablation features on Si (100) produced with seven laser pulses at peak fluences shown. (a) Feature produced with peak fluence of showing pitted damage ring surrounding undamaged Si and a central damage crater. Arrow indicates outer damage ring. (b) Image of inset from (a) showing detail of pitted damage ring, central damage region and intermediate undamaged region. (c) Feature produced with peak fluence of pulses showing only ring of damage surrounding a relatively undamaged region. (d) Feature produced with peak fluence of pulses showing pitted damage region. (e) Feature produced on atomically clean Si (100) with 7 laser pulses of peak fluence of . Notice the absence of any damage ring feature.
Gaussian fluence spatial profiles superimposed over relevant fluence thresholds. (a) Peak fluence of pulse at center of pulse greater than damage threshold of , resulting in features like those made with peak fluence of shown in Fig. 1(a). (b) Peak fluence of pulse less than damage threshold of but greater than modification threshold, resulting in no material removal at the center of the feature, as in the feature in Fig. 1(c). (c) Peak fluence less than the modification threshold of , but greater than damage threshold of Si (100), resulting in a pitted elliptical damage feature, as shown in the SEM image in Fig. 1(d).
OM images (in Nomarski mode) of grazing incidence feature morphology as a function of number of laser pulses. Features produced with pulse fluence of in air, with number of pulses shown. Scale is the same for all images. The undamaged region fills as the number of pulses increases, eventually filling in completely after 15 pulses.
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