低折射率材料非线性光学响应的微扰描述之外
Beyond the perturbative description of the nonlinear optical response of low-index materials
摘要：
我们表明，在非线性光学的标准近似违反的情况下，涉及一个小的线性折射率值。因此，传统的强度相关的折射率方程，$n(I) = n_0 + n_2 I$，变得不适用于ε-接近零和低折射率的介质，即使在只有三阶效应的存在。对于铟锡氧化物的特殊情况下，我们发现，$χ^{(3)}$，$χ^{(5)}$和$χ^{(7)}$的贡献，折射日食的线性项，因此，非线性响应可以不再被解释为在这些材料的扰动。虽然响应是非微扰的，我们没有发现证据表明，材料的极化的幂级数展开发散。
英文摘要：
We show that standard approximations in nonlinear optics are violated for situations involving a small value of the linear refractive index. Consequently, the conventional equation for the intensity-dependent refractive index, $n(I) = n_0 + n_2 I$, becomes inapplicable in epsilon-near-zero and low-index media, even in the presence of only third-order effects. For the particular case of indium tin oxide, we find that the $χ^{(3)}$, $χ^{(5)}$ and $χ^{(7)}$ contributions to refraction eclipse the linear term; thus, the nonlinear response can no longer be interpreted as a perturbation in these materials. Although the response is non-perturbative, we find no evidence that the power series expansion of the material polarization diverges.
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