1. In the lecture, we have derived the expression of second order susceptibility as χ (2) (ω1 + ω2, ω1, ω2) = Ne3a ε0m2D (ω1 + ω2) D (ω1) D (ω2) (a) Based on this result, show Miller’s rule: the quantity χ (2) (ω1 + ω2, ω1, ω2) χ(1) (ω1 + ω2) χ(1) (ω1) χ(1) (ω2) is almost a constant for all noncentrosymmetric crystals. (b) By writing ω3 = ω1 + ω2, show that χ (2) (ω3, ω1, ω2) = χ (2) (ω1, ω3, ω−2) = χ (2) (ω2, ω3, ω−1)