Ultrabroadband Optical Limiting via Reversible Polystyrene Nanoparticle Clouding: Phase Diagram for Laser Intensity and Concentration Thresholds

Optical limiting is a critical mechanism in photonic systems, protecting sensitive optical devices by attenuating high-intensity light to prevent damage through decreased light transmission. This study investigates ultra-broadband optical limiting via reversible clouding of polystyrene nanoparticles (196nm, 108nm, 52nm in diameter) in an aqueous medium, induced near the phase separation boundary by optical trapping. Polystyrene particles can exist as a homogeneous one-phase solution where they are uniformly suspended, but near the phase separation boundary, they transition into a heterogenous two-phase system that blocks incoming light. The boundary corresponds to the concentration conditions where particles shift from one-phase to two-phase. Optical trapping via focused electromagnetic radiation locally increases the particle density, driving the system into the two-phase region.

This clouding effectively reduces light transmission and is also reversible, with particles dispersing into the one-phase system when optical trapping is removed or if the light intensity is below the threshold. This study aims to construct a phase diagram mapping sufficient laser intensity for the optical trap and the polystyrene mass fraction concentration for effective optical limiting.