We present theoretical and experimental investigations of factors that may influence the surface quality of insulators patterned by 157 nm F2 laser ablation. Aspects covered include modelling of beam spatial coherence and diffraction effects for proximity mask exposure, and the role of melt relaxation on surface microstructures. Experimental results for micron-scale patterning of N-BK7 glass and NaCl crystals using proximity masks are presented and discussed within the framework of the modelling.