Broadband and reversible optical limiting via optical trapping in saturated colloidal vapors: an experimental study of dynamic response and intensity limiting threshold.

Robust, broadband optical limiting is essential for protecting photonic and imaging systems from high-intensity laser damage. Prior approaches in light-induced colloidal phase transitions and resulting liquid aggregate as optical limiting mechanisms required high trapping power to trigger transition due to high osmotic resistance. This study present a dynamically tunable and reversible optical limiting mechanism based on light-induced colloidal phase transitions at the liquid-vapor phase boundary. Aqueous samples of Pluronic-coated 187nm polystyrene (PS) nanoparticle colloids, polyethylene glycol (PEG) as polymer depletant, and KCl salt to modulate Debye length are prepared at the phase boundary. At this point, sample osmotic compressibility diverges and osmotic resistance to trapping is null. Phase transitions are triggered using continuous-wave 1064nm or 532nm Nd:YAG optical trapping lasers to locally increase osmotic pressure. At varying depletant concentrations and trapping wavelengths, this study determines the power threshold to trigger aggregation and dynamic response of saturation and relaxation. In conclusion, characterization of the optical trapping response reveals the potential for robust, reversible, broadband optical limiting.