Backward second-harmonic generation. Part (c) of Fig. 2.1.1 implies that second-harmonic generation is radiated in the forward but is not appreciably radiated in the backward direction. Verify that this conclusion is in fact correct by deriving the coupled amplitude equation for a secondharmonic field propagating in the backward direction, and show that the amplitude of this wave can never become appreciable. (Note that a more rigorous calculation that reaches the same conclusion is presented in Section 2.11.)
