Experimental investigations and thermal calculations of laser induced backside wet etching (LIBWE) of fused silica are presented. Fused silica plates having 1 mm thickness were irradiated by an ArF excimer laser in the presence of liquid absorber. The absorbing liquids were naphthalene-methyl-methacrylate solutions with different concentrations (0, 0.21, 0.43, 0.85 and 1.71 mol/dm(3)). The absorption coefficients (alpha) of these solutions at the applied wavelength were determined using a plano-concave microcuvette. It was found that the value of alpha could be varied in the range of 39400-62300 cm(-1) by the change of the naphthalene content. The dependence of the etch rate on both the absorption coefficient of the liquid absorbers and the applied fluence was studied. The etch depths were measured by an atomic force microscope. At 450 mJ/cm(2) laser fluence, the etch rates were found to be between 13.3 and 22.2 nm/pulse depending on the actual absorption coefficient. In the next experiment the laser fluence was varied from 110 to 860 mJ/cm(2) and the etch rate was found to vary between 4.7 and 49.5 nm/pulse when the concentration of the applied solution was constant 0.85 mol/dm(3). The mechanism of the LIBWE can be explained in the first approximation by thermal effects and their consequences. We calculated the maximal depth of melted fused silica layer by numerical solution of the one-dimension heat flow equation taking into account the phase transformations of the liquid reagents and the fused silica target. These calculations proved that the thickness of the melted quartz layer depends linearly on both of the absorption coefficient of the liquid and the laser fluence. Our calculations give an upper estimation of the etch rate. On the basis of our results a possible interpretation of the LIBWE was suggested. (C) 2003 Elsevier B.V. All rights reserved.