Powerful ultraviolet laser pulse impact on polished metals and semiconductors

Laser treatment for samples of copper, its alloys and gold was carried out with a UV pulse of nanosecond duration. After irradiation at subthreshold values of the energy density (E ∼ 0.2 - 0.8 J/cm²) the noticeable changes in the surface layer were revealed. These are traces of thermoplastic deformation resulting from laser exposure. They appear as uneven rise of the irradiated sample surface area up to 1 μm. The effect is cumulative, because the height of the uplifts increases with increasing number of impact pulses. In addition, the characteristic features of high-temperature plastic deformation were observed in the form of crystallographic slip and grain-boundary slippage. At E ∼ 1 J/cm² or more the optical breakdown occurred with the formation of a crater on the metal surface, that precludes the detection of described effects. The mechanical impulse of a laser plasma, when exposed to a metal surface, prevents the thermomechanical expansion of the material, and therefore, similar effects have not been previously observed. On the surface of materials with a significantly larger elastic limit (single crystals of germanium and silicon, a tungsten carbide) this phenomenon was not observed, because the generated thermomechanical stresses were insufficient to create conditions of plastic deformation.