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A new model for the ablation of microstructures with excimer laser radiation is presented. The model is based on an interactive two-step approach. The local distribution of the light over the developing structure is evaluated for each pulse. This distribution is then used to calculate the local etch rate, and hence the change to the structure. Despite the assumptions inherent in the model, in particular assumptions made about the propagation of the light through a developing structure and about the etching behavior of the materials, results from the model agree with actual aspects of ablated structures. The model has been used with some success to predict the wall angles of trench structures ablated using partially coherent illumination from a fly's eye homogenizer. Predictions of the model show good agreement with the experiment results. In particular, the model correctly predicts the variation of the wall angles with incident fluence and also predicts structures with well defined wall angles over depths much greater than the depth of focus of the image.

We describe a general investigation into the scattering of light by human hair. The main features of the intensity distribution produced by light scattered by an individual hair are identified. Qualitative explanations for the features are advanced in terms of the arrangement of the outer structure of the hair and its level of pigmentation. Contrast gloss values are calculated in an attempt to quantify the appearance of hair. These values are found to depend not only on the properties of hair, such as color and condition, but also on the direction and polarization state of the incident light. In assessing the effects of cosmetic treatments on hair, gloss values are shown to be useful where readings from treated hairs are compared with those from a control sample investigated in the same conditions.

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