  The PhD thesis is devoted to the study of second harmonic generation of
narrow beams in photonic crystals. The basic idea is that if both frequencies,
the fundamental and second harmonics are in the region of self-collimation,
then the second harmonics of narrow beams can be very efficient. The beams do
not spread diffractively during propagation and interaction. The phase matching
is ensured for all components of the interacting beams. This allows to enhance
the nonlinear interaction efficiency several times. The thesis rewises the
theory of self-collimation of narrow beams in photonic crystals, and presents
the theory of second harmonics in photonic crystals. Calculations in photonic
crystals of different configurations are presented, and the recommendations to
experimental realisations are given.
