Optical limiting of pentaazadentate complexes in solution for nanosecond pulses

Passive optical limiters are significant for protecting sensors and human e yes from high intensity laser. The selection of materials is still the key point for optical power limiters. The optical limiting performances have be en 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 puls es, in which the reverse saturable absorption from the triplet-->triplet ex cited state is responsible for the optical limiting. The optical limiting t hresholds at T/T-0 = 0.5 are 139 mJ/cm(2), 350 mJ/cm(2) and 420 mJ/cm(2) fo r [(PMC-NO2)Cd]CI, [(PMC-Np)Cd]CI, and [(PMC)Sm]CI, respectively. The lowes t nonlinear transmittance for [(PMC-NO2)Cd]CI is 10%, while the incident ma ximum fluence reaches to 600 mJ/cm(2). The ratios of T-0/T-lim, are estimat ed at 2.3 to 9.0. The limiting thresholds are strongly influenced by the na ture of the substituents on the benzene ring and the heavy atom effect. Ele ctron withdrawing groups of the complexes can enhance the limiting capabili ty, and the heavy atom effect facilitates the decreasing of the limiting th reshold. (C) 2001 Society of Photo-Optical Instrumentation Engineers.