Thin films of a photosensitive material based on polymethyl methacrylate have been fabricated on glass substrates. By illumination with light of a photoresist illuminator (300–450 nm) the material can be etched out in the illuminated areas. Film thicknessdchanges from, e.g., 12 to 4 &mgr;m after 20‐min illumination. Simultaneously the refractive indexndecreases by 2×10−2. Additional annealing treatment causes little further development ofnanddpatterns. Spatial resolution is limited by lithographic technique and is smaller than 1 &mgr;m.