Inverse scattering in an asymptotically flat multilayer domain
We consider a scattering problem for a wave equation $\partial_t^2 u = \frac{1}{\sqrt{g}}\partial_i(\sqrt{g}g^{ij}\partial_j)u$ in a multilayer domain $Ω\subset {\bf R}^{n+1}_x = {\bf R}^n_y \times {\bf R}^1_{x^{n+1}}$ of the form $Ω= \mathcal K \cup Ω_1 \cup \cdots \cup Ω_N$, where $\mathcal K$ is a bounded open set and $Ω_k$ is asymptotically equal to a slab domain ${\bf R}^n \times (c_k,c_k + d_k)$ as $|y| \to \infty$. Assuming that $\partial_x^α\big(g_{ij}(x) - δ_{ij}\big) = O(|x|^{-|α| - δ_0}), \ δ_0 > 1, \forall α$, we show that $Ω$ and $g^{ij}$ are determined by one diagonal component $S_{11}(λ)$, for all energies, of the S-matrix associated with the slab $Ω_1$, provided $Ω_1$ is flat: $Ω_1 \cap \{|y| > R\} = \{|y| > R\} \times (c_1, c_1+d_1)$ for some constants $c_1, d_1, R > 0$, and the metric is Euclidean on $Ω_1\cap \{|y| > R\}$.