Angle-dependent laser diffraction in inverse opal photonic crystals

We discuss the experimental data on laser diffraction in photonic crystal films with an inverse opal structure. Inverse opals based on tungsten, manganese and titanium oxides were prepared by replicating colloidal crystals made of 900 nm polystyrene microspheres. We scanned both colloidal crystals and inverse opals with a 532 nm laser beam and recorded symmetrical sixfold diffraction patterns for all samples studied. By using diffraction data we calculated the period of the photonic crystals and examined their crystalline quality; both parameters were found to be in good agreement with the scanning electron microscopy results. Thus, laser diffraction can be considered as a method to visualize the shrinkage of photonic crystal samples that occurs in their transformation from colloidal crystals to inverse opals in a replicating process.