Beam modulation caused by the plasma scalds in the multilayer dielectric films.

The near-field phase modulation (NFPM) caused by the plasma scalds is investigated with a newly proposed mixed overcoat layer model. Based on the NFPM, the far-field intensity modulation (FFIM) is calculated and discussed with the scalar diffraction theory. The results indicate that both the NFPM and FFIM are sensitive to the scalding depth. A feature curve is developed to analyze the NFPM for arbitrary scalding depth. The modulation can be ignored when the scalding depth is less than the first feature point in the feature curve. Even though the diffraction intensity in the Fresnel region can be enhanced dozens of times, the FFIM in the Fraunhofer region can recover gradually if the scalding depth is below a critical value. The preliminary experimental results are consistent with the theoretical prediction. (C) 2015 Optical Society of America