Nanosecond cw Visible-IR All-Optical Switching and Nonlinear Transmission with a Nonlinear Organic Optical Liquid in Bulk and Guided Wave Geometry

Passive all-optical protection against such multiple time-scales and extremely broadband intense light sources is rather challenging due to the fact that an optical limiting mechanism that is efficient in one time scale usually become rather inefficient in another time scale. Nonlinear absorptions such as Two-Photon absorptions [TPA] and Excited State absorption [ESA] that are effective for limiting nanosecond laser pulses simply do not work in the microseconds and longer time scales as a result of the reduction in power/intensity for the same energy flux. In these time scales, a variety of approaches and materials, including dye-doped aligned nematic liquid crystals, have emerged as promising alternatives [1, 2]. In this presentation, we describe another promising organic material that enables all-optical switching in an extremely wide time scales spanning sub-nanoseconds to cw regime a nonlinear neat organic liquid (L34) in bulk or wave-guided [fiber core] structure. In the visible spectrum [400 -700 nm], quantitative z-scan and pump-probe techniques [3, 4] have shown that in the sub-nanosecond time scales, the dominant nonlinear absorption processes are two-photon coupled to excited state absorption processes characterized by an intrinsic two photon absorption coefficient of ~5 cm/GW, and an intensity dependent effective two-photon absorption coefficient that can be over 200 cm/GW. For longer time scales, the transparency of the liquid allows doping with appropriate absorbers to generate efficient thermal/density and nonlinear scattering effects [as well as guided mode extinction in fiber geometry] for all-optical switching