Fengqi Guo Institute of Photographic Chemistry (China) Wenfang Sun Univ. of Alabama/Birmingham (United States) Duo-Yuan Wang Institute of Photographic Chemistry (China) Yinglin Song Harbin Institute of Technology (China)
Passive optical limiters are significant for protecting sensors and human eyes from high intensity laser. The selection of materials is still the key point for optical power limiters. The optical limiting performances have been measured for six new pentaazadentate metal complexes with initial linear transmission of 0.90 in a 2 mm cell in chloroform at 532 nm with 8 ns pulses, in which the reverse saturable absorption from the triplet?triplet excited state is responsible for the optical limiting. The optical limiting thresholds at T/T0 = 0.5 are 139 mJ/cm2, 350 mJ/cm2 and 420 mJ/cm2 for [(PMC-NO2)Cd]Cl, [(PMC-Np)Cd]Cl and [(PMC)Sm]Cl, respectively. The lowest nonlinear transmittance for [(PMC-NO2)Cd]Cl is 10%, while the incident maximum fluence reaches to 600 mJ/cm2. The ratios of T0/Tlim are estimated at 2.3 to 9.0. The limiting thresholds are strongly influenced by the nature of the substituents on the benzene ring and the heavy atom effect. Electron withdrawing groups of the complexes can enhance the limiting capability, and the heavy atom effect facilitates the decreasing of the limiting threshold.