In the case when Λ=0.2Λ=0.2 and N=30N=30, the distribution of the second-harmonic amplitude in the layered structure is shown in Fig. 7 for different normalized fundamental frequencies. Note that RG7388 the amplitude exhibits stepwise variation across the interfaces and remains constant in each layer, since the layers are linearly elastic. For Ω/π=0.1Ω/π=0.1 and 0.3, both the fundamental and the double frequencies are in the first pass band. As a consequence, the second-harmonic amplitude increases cumulatively with distance for the region 0<x/h<300<x/h<30 in which the nonlinear interfaces lie. For Ω/π=0.4Ω/π=0.4, the fundamental component can propagate through the structure and generate the second-harmonic component at 30 interfaces, but the second-harmonic field has a standing-wave nature and does not propagate away to infinity since the double frequency is in the first stop band. For Ω/π=0.5Ω/π=0.5 and 0.6, the fundamental and the double frequencies are in the first and the second pass bands, respectively, but due to the dispersive nature the second-harmonic amplitude oscillates with certain wavelengths mainly governed by ΔK(Ω). For Ω/π=0.8Ω/π=0.8, estrogen frequencies are in the first and the second stop bands, respectively, so the fundamental component decays for x/h>0x/h>0, which only accompanies the second-harmonic generation in a localized nature. For Ω/π=1.1Ω/π=1.1, both frequencies are in the pass bands and the cumulative nature of second-harmonic generation is recovered due to the approximate phase matching near Ω=πΩ=π.
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