Optical Limiting and the Potential Role of Organic Materials

Abstract

We will present a brief review of past work on passive sensor protection devices including the materials studied (e.g. semiconductors, organics and ink) and some of the requirements of optical limiting devices. The nonlinear mechanisms potentially useful for optical limiting include nonlinear absorption, nonlinear refraction and nonlinear scattering. We present methods for characterizing nonlinear materials using Z-scan and related techniques and describe ways to differentiate the nonlinear mechanisms. We will specifically discuss two-photon absorption and excited-state absorption (referred to as reverse-saturable absorption), as well as bound electronic n2 and excited-state refraction. We also show how to examine organic thin films using a modified Z-scan with enhanced sensitivity called EZ-scan. The organic materials studied include phthalocyanine and polymethine dyes. The potential of organics for real optical systems remains to be seen. For example, the most promising organic limiting materials are effective over somewhat smaller spectral ranges than desired. Mixing of different materials in solution or solid matrices may extend the spectral range, and potentially extend the dynamic range as well.