Third-order optical nonlinearities of alpha,omega-dithienylpolyenes and oligo(thienylvinylene)

alpha,omega-Dithienylpolyenes and oligo(thienylvinylene) are interesting third-order nonlinear optical materials for a variety of device applications. To better understand the third-order nonlinear response of these materials, the third-order susceptibilities (chi((3))) and nonlinear absorption behaviors of two alpha,omega-dithienylpolyenes with different conjugation length and two oligo(thienylvinylene) with different substituents on the thiophene rings have been studied using degenerate four wave mixing (DFWM) and nonlinear transmission techniques at 532 nm. The chi((3)) values of 1 x 10(-3) mol/l solutions are all of the order of 10(-13) esu. The chi((3)) values increase with the increase of the linear absorption coefficient. In addition, these compounds exhibit reverse saturable absorption for nanosecond laser pulses. The strength of reverse saturable absorption varies when the conjugation length and substituents change. Moreover, the nonlinear absorption characteristics of these compounds in the picosecond regime differ from those in the nanosecond regime. The different nonlinear absorption behavior is due to the relative contributions from excited singlet-singlet and triplet-triplet absorption. The strong reverse saturable absorption characteristics of two of the compounds suggest that they could be potential candidates for optical limiting applications in the nanosecond regime. (C) 2002 Elsevier Science B.V. All rights reserved.