Surface-emitting SHG

In terms of the SHG efficiency, one would expect to see a trade-off between the enhancement of the nonlinear d coefficient on resonance and the low off-resonant absorption. From the calculated efficiency, however, it is apparent that influence of the absorption dominates and better performance is typically achieved off resonance. This is true for copropagating SHG, only. For surface-emitting SHG, for example, operation on resonance is favorable [21]. 

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