Reflection properties of oriented thin CdS films formed by laser ablation

Oriented thin (≈2 μm) films, CdS, prepared by laser ablation were characterized by the dependence of external and internal reflection on both the angle of incidence and the polarization of laser light. The samples exhibit perpendicular and parallel orientation of the crystallographic axis with respect to the surface of the glass substrate. The experiments were performed at 300 K using low intensity (<1 W/cm²) cw emissions at 476.5, 514.5 and 632.8 nm of argon and He–Ne lasers respectively. For blue and green light, the results are very well described by the theoretical models based on Fresnel reflection. In contrast to the external features, the internal reflectance exhibits dichroism and birefringence of the samples at 514.5 nm, revealing the sensitivity of the internal reflection technique to the optical anisotropy of the films. Considering multiple-beam interference, the model of Fresnel also describes satisfactorily the results for red light. However, a rather sensitive dependence on the incoming He–Ne laser intensity was observed. In fact, by increasing the intensity of 64 mW/cm² by about one order of magnitude, only the external reflectance shows good agreement with the theory, whereas the internal reflection properties are obviously influenced by additional effects, such as non-linear change of the optical constants, which are not included in Fresnel reflection considerations.