Influence of light scattering on the development of laser-induced ridge-cone structures on target surfaces

A new model of light-target interaction, which takes into account multiple interaction of the scattered laser beam with the surface structure of a tar get, is reported. The model is based on calculations of the local intensity of the electromagnetic wave, from which the local amount of ablated materi al can be obtained after each simulated laser pulse. The simulations of the sequence of laser pulses was employed to explain the observed development of the particular surface topography. It is shown that during laser ablatio n a small initial surface roughness is sufficient to initiate further deepe ning of the surface relief. During this preliminary development of the reli ef, the 1(st)- order scattering plays a dominant role. But, as soon as the surface acquired a relatively deep relief, the 2(nd)-order interaction lead s to the appearance of "hot" valleys, where the electromagnetic energy of t he light wave is significantly more concentrated and, therefore, the ablati on is more efficient. As a result of this effect the depth of the valleys i ncreases and the cone structure becomes more and more pronounced.