论文标题
天体物理镜头方案：折射光学，衍射光学和菲涅尔尺度
Regimes in astrophysical lensing: refractive optics, diffractive optics, and the Fresnel scale
论文作者
论文摘要
天体物理镜头通常在两个方向上进行了研究：衍射光学和折射光学。衍射光学元件的特征在于Kirchhoff-Fresnel衍射积分的扰动膨胀，而折射光学元件的特征是固定相近似。以前，已经假定菲涅尔量表$ r_f $是将这两个制度分开的相关物理量表。随着Picard-Lefschetz理论的最新引入镜头领域，已经有可能将离散图像的屈光化描述概括为所有波参数，尤其是在所有频率下都可以准确地评估衍射积分。在这项工作中，我们通过与此精确评估进行比较，评估了简单的一维透镜模型的折射率和衍射近似值的有效性。我们发现，与以前的假设相反，这些机制之间的真实分离量表由$ r_f / \sqrtκ$给出，其中$κ$是镜头的收敛性。因此，当镜头很强时，折射光学可以用于任意小尺度。我们还认为，衍射光学器件的强度变化通常很小，这对研究强衍射闪烁（DISS）的研究具有影响。
Astrophysical lensing has typically been studied in two regimes: diffractive optics and refractive optics. Diffractive optics is characterized by a perturbative expansion of the Kirchhoff-Fresnel diffraction integral, while refractive optics is characterized by the stationary phase approximation. Previously, it has been assumed that the Fresnel scale, $R_F$ , is the relevant physical scale that separates these two regimes. With the recent introduction of Picard-Lefschetz theory to the field of lensing, it has become possible to generalize the refractive description of discrete images to all wave parameters, and, in particular, exactly evaluate the diffraction integral at all frequencies. In this work, we assess the regimes of validity of refractive and diffractive approximations for a simple one-dimensional lens model through comparison with this exact evaluation. We find that, contrary to previous assumptions, the true separation scale between these regimes is given by $R_F / \sqrtκ$, where $κ$ is the convergence of the lens. Thus, when the lens is strong, refractive optics can hold for arbitrarily small scales. We also argue that intensity variations in diffractive optics are generically small, which has implications for the study of strong diffractive scintillation (DISS).
