Role of two-photon states in nonlinear optical dye chromophores

摘要

The critical role of two-photon $pi@-electron excited states in third order optical processes in squaraine dyes is described. The discussion is based on recently completed femtosecond measurements of the excited state absorption spectrum of a typical centrosymmetric squaraine. The new experimental data agree well with the earlier theoretical description and quantum many-electron calculations reported for the dye chromophores.