Conical structures produced by excimer laser irradiation of polymers

The development of conical structures on the surface of excimer laser ablated polymers, is studied. It is demonstrated that this phenomenon has a lower threshold and an upper limit fluence which values depend on the material. The lower value is equivalent of the ablation threshold of the sample, below which the etch does not occur. In accordance with our assumption the upper limit corresponds to the ablation threshold of the particulate impurities which are responsible for the formation of cones, because these impurities remove from the surface of the polymers with the other ablating fragments when the fluence exceeds the upper limit. The dependence of the apex angles of the cones on the fluence and the number of pulses is investigated. A simple etching model based on the diffraction and interference theories is proposed to explain the formation of the conical structure.