The scanning etching on Si, GaAs and Zn plates with a frequency doubling Ar+ laser at 257.3 nm is reported. The width of the smallest etched line 1.2μm was obtained. The dependence of the etching depth on the light intensity/scanning rate is given. The diffusion coefficient, free path of the halogen radical and scale of laser focused spot were estimated for the first time by the method of the laser etching technique. A threshold phenomena was observed and explained.