Beating photo-degradation in sum-frequency imaging of chiral organic media

• Sum-frequency imaging in optically active materials is re-examined.
• Irreversible photolysis is evidenced for a large panel of conjugated molecules.
• The induced changes in emission properties are found to be permanent in all cases.
• High signal level operating conditions which minimize degradation are established.
• Multi-photon induced luminescence may provide complementary informations.

Sum-frequency generation from chiral bulk media holds the promise of a powerful tool in the investigation of biological as well as artificial materials containing optically active elements. Since this technique is based on a nonlinear optical effect, the high intensities of the illuminating light sources may induce spurious artifacts. Using simple conjugated chromophores, we demonstrate that multi-photon induced irreversible photolysis may be avoided while keeping undiminished levels of sum-frequency signals. In addition we show that the concurrent multi-photon induced luminescence may provide complementary means of imaging samples.