Two-photon Absorption Study With Coupled Mode Formalism

Optical limiting devices employ two photon absorption in materials for sensor and eye protection. To be able to reduce the intensity threshold for protection, cavity structures can be considered. However, design of structures by solving full solution to nonlinear Maxwell equations in the cavity is tedious and obscures the relationships between controllable parameters and the limiter performance. In this article, we extend the coupled mode formalism to include two photon absorption and derive simpler equations connecting these design parameters and the optical performance. The analytical solution enables the identification of material parameters and threshold intensity required to meet the preferred limiter performance. We demonstrate that our solution is highly accurate by comparing it with a full solution to Maxwell Equations in a HgCdTe-based cavity, designed to reject 10.6 μm wavelength light. Equally importantly, we note that the design acts as a near-perfect reflector when the incident intensity is larger than a certain low threshold intensity and thus does not reach the limiter damage threshold.