Transparent materials can be etched with high quality by laser-induced back side etching at low fluences. The etch rates and the surface topography have been studied to some extent but little is known about the properties of the etched surface. The composition of etched quartz and fused silica samples are studied by RBS, XPS and Raman spectroscopy for different processing parameters and processing modes. With increasing laser fluence the amount of surface contaminations rises and the amorphization of crystalline quartz grows. At certain conditions an amorphized surface layer as thick as only 2 nm has been observed. Hence, a precise material processing characterized by a low damage of the material surface and only a small deposition of contamination layers can be achieved by back side etching but it requires well chosen processing parameters and an appropriate processing mode. (C) 2003 Elsevier B.V. All rights reserved.