Nonlinear properties and kinetics of some donor-acceptor optical limiting molecules

The nonlinear optical properties of four novel azulene-type donor-acceptor compounds have been measured by means of the two-dimensional Z-scan technique. These compounds exhibit considerable nonlinear refraction and one shows strong nonlinear saturated absorption at 527 nm. The transient spectra and kinetics, after excitation of the charge-transfer absorption band, have been studied by means of a picosecond transient absorption spectroscopy, allowing us to measure absorbance changes as small as Delta A=0.005 and time resolution of 1.5 ps. Several compounds exhibited quite strong reversed saturable absorption in a wide region of the visible spectrum. The reversed saturable absorption induced an increase in the effective absorption of the material at high power, which suggests that, it maybe useful as an optical limiting medium.