Abstract

We report the results of studies of laser-generated ripple patterns on intermediate gap semiconductors (e.g., ZnS, ZnSe) and dielectrics of various indices of refraction. The experiment has been carried out at normal incidence using mainly a CO₂ TEA laser which produced TEM₀₀ pulses of 150-ns duration. Preliminary results of irradiation with 1.06 µm, 15-ns pulses have also been produced. The results confirmed the formation of coherent structures on the front or rear surface of a damaged material. In particular, for a variety of transparent dielectrics, we carefully determined the ripple spacing (X/n) through microscopic observation and by diffraction pattern measurements. The ripple spacing and direction are in gross agreement with prior observations by other workers. Similar measurements on front and rear surfaces of ZnS and ZnSe revealed the presence of domains of regularly spaced ripple formations and fine structure superimposed parallel to the main pattern. Such fine structures are also present in the damaged dielectric samples although to a much less extent. Furthermore, a wrong orientation (parallel to the applied electric field) of the induced gratings was sometimes observed. The observed ripple spacings and orientation for ZnSe and ZnS cannot be completely explained with existing models.

© 1985 Optical Society of America