Optical control of third-harmonic generation in azo-doped polymethylmethacrylate thin films

The possibility of controlling third-harmonic generation in polymethylmetha crylate doped with disperse red 1 via exposition by frequency-doubled and f undamental radiation of a Nd:YAG laser is demonstrated. It was possible to change the third-harmonic efficiency up to four times depending on pumping intensity. The change was completely reversible after 15 min of dark relaxa tion in the case of pumping the sample with the second harmonic. This effec t is attributed to the reversible change of third-order susceptibility due to trans-to-cis isomerization of azo-bond molecules. (C) 2000 American Inst itute of Physics. [S0003-6951(00)02840-0].