| We studied the effect of different auxochromes on the optical nonlinearities of hemicyanine dyes and designed a single-shot pump-probe technique,which provide important references for optimizing the nonlinear optical properties of organic chromophores and designing single-shot pump-probe technique.Two hemicyanine dyes Hemicyaninel and Hemicyanine2 with different auxochromes were successfully synthesized and characterized by carbon and hydrogen NMR spectroscopy.UV-Vis and fluorescence spectra showed that both hemicyanine dyes have similar linear absorption and near-infrared fluorescence characteristics.Broadband nanosecond Z-scan measurements and 532nm picosecond Z-scan measurements showed that both hemicyanine dyes have reversesaturable absorption and Hemicyanine2 is significantly stronger than Hemicyaninel.In nanosecond regime,multi-energy Z-scan measurements and optical limiting experiment demonstrated the reverse-saturable absorption of both hemicyanine dyes derives from onephoton induced excited state absorption and occurs saturation as the light intensity increases.To explain the different in optical nonlinearities of two hemicyanine dyes,we measured the transient dynamics of both using femtosecond transient absorption spectra.Through analyzing and comparing the transient absorption spectra of both hemicyanine dyes,we conclude that:1.Different auxochromes can fine-tuning the overlap degree between the excited state absorption and the ground state absorption;2.In a polar solvent,different auxochromes can significantly influence the lifetime of excited state in hemicyanine dyes.These results demonstrate that auxochrome plays an important role in optimizing the nonlinear optical properties of hemicyanine dyes.In addition,we designed a single-shot pump-probe technique.We measured the two-photon absorption of GaN crystal successfully at a wavelength of 515 nm using this technique,a result that demonstrates the validity of this technique. |
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