Saturable Absorption in Solution-Phase and Cavity-Coupled Tungsten Hexacarbonyl

Saturable absorption, in which optical absorption decreases as the incident intensity increases, is commonly utilized in the visible and near-infrared for laser applications. In the mid-infrared, most vibrational transitions are too weak and optical fluences too low to achieve saturable absorption. In this work, we demonstrate saturable absorption in a narrow band centered at 1983 cm(-1) in solution-phase W(CO)(6) with a readily accessible saturation fluence. Furthermore, in a system where coupling between the strongly absorbing vibrational mode of W(CO)(6) and an optical cavity gives rise to two polariton modes (i.e., the strong coupling regime), we demonstrate that saturation of the splitting between polariton peaks leads to a fluence-dependent cavity transmission with a saturation fluence that scales counterintuitively with the cavity length and molecular concentration.