Tyndall Windows: Tunable Scattering of Disordered Solid–Liquid Matching Mixtures

We explain and explore sharp optical diffusion modulations of solid–liquid matching mixtures. The technique is based on sole refractive index modulation mismatch of optically matching materials at different states. This enables basic materials such as glass-based mixtures to obtain a sharp window of transparency at a desired condition. Our demonstration indicates over 3 orders of magnitude optical transmission modulation with 0.03 thermally induced modulation of the refractive index mismatch. The narrow full width at half maximum of this diffusion modulation is the result of Tyndall scattering of densely packed irregular particles that is not fully explainable by Mie theory. Such mixtures can be used as tunable phantoms and have applications in optofluidics, rheology, and cytometry.