通过界面处波长尺度光学梯度对临界角附近内反射率的影响探测和分析
Detecting and analysing wavelength-scale optical gradients at an interface by their effects on the internal reflectance near the critical angle
摘要：
光在临界角附近的内反射率对入射角和界面附近外部介质的光学性质非常敏感。亚临界内反射在生物学和医学中的新应用正在被追求。在许多实际情况下，由于表面的不同物理现象，外部介质的折射率可能相对于其体积值而变化。因此，迫切需要了解近临界角反射表面折射率梯度的影响。在这项工作中，我们从理论上研究了临界角附近的反射率与玻璃的界面假设外部介质具有连续的深度依赖的折射率。我们提出的内部反射率作为入射角的函数，表现出在界面处的折射率梯度的影响的图形。我们分析了在实现全内反射之前反射率曲线的行为。我们的研究结果提供了深入了解如何可以认识到存在的折射率梯度在界面上，并揭示了其特征的可行性。
英文摘要：
Light's internal reflectivity near a critical angle is very sensitive to the angle of incidence and the optical properties of the external medium near the interface. Novel applications in biology and medicine of subcritical internal reflection are being pursued. In many practical situations the refractive index of the external medium may vary with respect to its bulk value due to different physical phenomena at surfaces. Thus, there is a pressing need to understand the effects of a refractive-index gradient at a surface for near-critical-angle reflection. In this work we investigate theoretically the reflectivity near the critical angle at an interface with glass assuming the external medium has a continuous depth-dependent refractive index. We present graphs of the internal reflectivity as a function of the angle of incidence, which exhibit the effects of a refractive-index gradient at the interface. We analyse the behaviour of the reflectivity curves before total internal reflection is achieved. Our results provide insight into how one can recognise the existence of a refractive-index gradient at the interface and shed light on the viability of characterising it.
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