The problem of second harmonic generation in uniaxial crystals at angles of synchronism close to 90° is considered at an assumed field approximation. It is shown that this important special case is characterized by a number of distinctive features, which were not discussed earlier and, what is more important, contradict to the common ideas of the physics of the considered process.
second harmonic generation, uniaxial crystal, 90°-synchronism, optimal wave length, optimal focusing