ИСТИНА

In the present work it is analytically shown that the appearance of SH signal in the bulk of isotropic chiral medium can be related with the non-locality or frequency dispersion of quadratic medium response in case of certain restrictions on spatial and temporal polarization distributions of the fundamental pulse. The research were carried out within negligible pump depletion approximation, parabolic approximation of diffraction theory and frequency dispersion was taken into account up to the second order. In the case of spatial non-locality of medium quadratic response to generate the SH pulse it is necessary for the fundamental beam to be in homogeneously polarised in its cross-sections. The polarization distribution in the SH signal is, however, not so inhomogeneous as that in the fundamental pulse. It was also analytically shown that in the case of spatially local, but frequency-dependent quadratic response of the medium the effective second harmonic generation can be achieved by using the fundamental pulse that is heterogeneously polarized in both space and time. The example of such pulse can be a sequence of two pulses that are homogeneously polarized in time but have different polarisation states and the time delay between them should not exceed the length of each pulse. As in the case of the media with non-local quadratic response the polarization state of the signal pulse at doubled frequency is more homogeneous in space and time compared to the fundamental pulse.