Optical limiting properties of derivatized carbothiacyanine dyes

The nonlinear optical absorption of a range of dialkyl-carbothiacyanine dyes has been measured using intensity dependent transmission measurements of the absorption cross-section at 532 nm. The ground and effective excited state absorption cross-section for each of the dyes has been determined. It was observed that with increasing bridge conjugation length between the carbothiacyanine end groups, the absorption cross section of ground state decreases slightly while the absorption cross-section of the excited state increases leading to an overall increase in the absorption cross-section ratio by an Order of magnitude from 0.3 to 5.29. The absorption cross-section ratio trades linearly with the difference between the energy of the pump laser and the energy of the ground state absorption. The counter lolls of the dyes also affect the nonlinear absorption significantly. These organic materials exhibit good potential for optical limiting applications.