Third-Order Optical Nonlinearities of Squarylium Dyes with Benzothiazole Donor Groups Measured Using the Picosecond Z-Scan Technique

Third-order optical nonlinearities of two squarylium dyes with benzothiazole donor groups(BSQ1 and BSQ2)in chloroform solution are measured by a picosecond Z-scan technique at 532 nm.It is found that the two compounds show the saturation absorption and nonlinear self-focus refraction effect.The molecular second hyperpolarizabilities are calculated to be 7.46×10^(−31) esu and 5.01×10^(−30) esu for BSQ1 and BSQ2,respectively.The large optical nonlinearities of squarylium dyes can be attributed to their rigid and intramolecular charge transfer structure.The difference inγvalues is attributed to the chloro group of benzene rings of BSQ2 and the one−photon resonance effect.It is found that the third-order nonlinear susceptibilities of two squarylium dyes are mainly determined by the real parts ofχ(3),and the large optical nonlinearities of studied squarylium dyes can be attributed to the nonlinear refraction.