Optical limiting in polar macromolecules in the nanosecond time range

The optical limiting by resonant two-photon absorption in polar media, such as some conjugated organic compounds with large polarizable π-electron system and biopolymers, is studied in terms of a three-level mixed-parity molecular system upon nanosecond laser irradiation. The two-photon absorption of polar medium is calculated and its effect on the transmitted laser intensity is analyzed. The numerical results indicate the dependence of the optical limiting efficiency on the magnitude of the permanent dipole moments of the electronic molecular states involved in nonlinear optical interaction between the laser electro-magnetic field and polar macromolecules.