Although polymethyl methacrylate (PMMA) is essentially transparent to light of 308 or 351 nm, it can be made sensitive to photoablation and etching by excimer laser pulses (20 ns half-width) of those wavelengths by the introduction of an organic dopant. The dopant (trade name=Tinuvin*) is actually a quencher of the first electronic excited state of PMMA and is therefore used commercially to stabilize the polymer against photodegradation. Laser etching of Tinuvin-doped PMMA can be shown to be a photochemical process in which the Tinuvin decomposes by the absorption of two or more photons and causes the ablation of the surrounding polymer.*[2-(2′-hydroxy-3′,5′-diisopentyl-phenyl) benzotriazole]. © 1988 Springer-Verlag.