UV laser modifications and etching of polymer films (PMMA) below the ablation threshold

The modification of thin polymethylmethacrylate (PMMA) films by the fifth harmonic (λ=216 nm) of a Nd:YAP laser is studied. This modification manifests itself in essential changes of optical properties, film thickness (bulk etching) and solubility in appropriate developers (crosslinking). The modification kinetics is investigated for films of different thickness, for different laser fluences (below ablation threshold), in air, and in vacuum. The nonreciprocal response not connected with laser heating has been obtained.