Nonlinear optical properties of a new chromophore

Strong two-photon-absorption (TPA) based nonlinear optical properties of a new chromophore, N, N-diphenyl-7-[2-(4-pyridinyl) ethenyl]-9,9-di-n-decyl-fluoren-2-amine (AF-50) has been experimentally studied. Under excitation with 10-Hz, ∼8-ns, and ∼800-nm laser pulses, the TPA cross section and the TPA-induced frequency-upconverted emission spectra are measured for AF-50 solutions in various solvents. The most attractive feature of this chromophore is its remarkably high value of the molecular TPA cross section (∼78 × 10^-20 cm²/GW in benzene solution). Based on this feature, superior optical power limiting and stabilization performance has been demonstrated in a 1-cm-long AF-50 solution sample with concentration of d₀ = 0.045 M/L. The nonlinear transmission of the measured sample decreased from ∼0.93 to ∼0.3 when the input-beam intensity increased from ∼10 MW/cm² to ∼360 MW/cm²; the relative intensity fluctuation of the output laser pulses was reduced to one third of that of the input laser beam.