ИСТИНА

Photonic crystals (PC) are periodic structures with a period of about the wavelength of a visible light. The simplest PC is an array periodically alternating dielectric layers of two types. At the Laue geometry (when the light propagates through the PC along the layers) the effects of the dynamical diffraction theory were observed, e.g. pendellösung effect and Borrmann effect. It was theoretically predicted that the femtosecond laser pulse at Laue geometry in 1d PC undergoes two consequent splitting: spatial and temporal. The spatial splitting is caused by the dynamical diffraction on the PC lattice and the temporal splitting can be explained as the formation of two spatial modes called borrmann and antiborrmann in a crystal and each of these modes is localized in layers of its own type. Therefore these modes have different group velocities depending on the refraction indices of two layers and these modes will split in time. The polarization dependence of the DIPS effect is crucial: splitting time value is 1.64 times higher for P-polarization than S. The theoretical estimation and numerical calculation for this ratio is of 1.4, i.e. the experimental result of polarization dependence is greater than theory predicts. This mismatching can be explained as material birefringence of annealed porous silicon.