The energy transfer to a metallic sample and the resulting thermal coupling depend strongly on the experimental conditions: incident fluence and intensity, pulse duration, pressure and nature of the surrounding gas. In order to optimize laser-material processing such as surface treatment (ablation, control of roughness, changes of the hardness, residual stresses or surface compounds) the expansion of the produced plasma in front of the surface must be studied. The purpose of this paper is to present an experimental study concerning the characterization of different plasma regimes using an interferometric method and a fast image converter camera. The samples (Ti alloy) have been irradiated from 5 J/cm2 to 130 J/cm2 using a 248 nm laser radiation. The experiments have been performed in various ambient gases (nitrogen, argon, air, and helium) under different ambient pressures (10-3 to 105 Pa). Time-evolved structures (spherical blast wave, LSC, LSD) have been shown depending on the experimental conditions.