An investigation of optical limiting on liquid crystals cored fibers.

摘要

A detailed analysis of optical limiting studies with picosecond and nanosecond laser pulses propagating within liquid crystal cored fibers are presented with theoretical models that explicate linear, two-photon, intermediate, excited-state absorptions and thermal/density effects. Specific expressions for the nonlinear transmission, optical limiting performance, laser induced changes of molecular level populations are obtained for laser pulses in both picosecond and nanosecond regimes. The theoretical simulations and experimental results provide a function to characterize the limiting effectiveness of L34 and other nonlinear fiber core liquid crystals. The optical characteristics induced by two-photon, intermediate state and excited-state absorptions are thoroughly examined for picosecond and nanosecond laser pulses, which propagate through the isotropic liquid crystals cored fibers, i.e., ILC and L34 cored fibers. In the picosecond regime, the optical limiting performance is contributed from all the nonlinear absorptions only, whereas there are significant limiting contributions from thermal/density effects detected in the nanosecond regime.; In practice, the compact millimeter-thick optical fiber arrays with liquid crystals guiding cores are developed to transmit high quality image of scenery, and provide human eyes and sensors with protection against agile laser pulses in visible spectrum. The feasibility of using these liquid crystals cored fiber arrays to limit the picosecond and nanosecond lasers pulses is demonstrated. The results show that they are capable of reducing the transmission to below the eye/sensor damage level.