Influence of Tm⁺³ concentration on the non-linear optical effects of the BiB₃O₆: TT^m3+ glass nanoparticle-doped polymer

It is shown that BiB₃O₆ : Tm³⁺ glass nanoparticles incorporated into polymethylmethacrylate (PMMA) and polycarbonate (PC) polymer matrices show good second-order susceptibilities under bicolour coherent laser treatment. It is found that only during incorporation into highly polarized PC matrices could one observe an enhancement of the second-order susceptibilities with increasing laser treated power densities. The main increase is observed for all samples at power densities equal to about 0.4 GW cm^-2. After passing this value there is a saturation of the output susceptibilities and even an abrupt decrease. The most striking feature is the achievement of second-order susceptibilities equal to about 5 pm V^-1 for samples containing 4% nanoparticle (NP) content in the PC matrix. A further increase in the NP concentration to 6% leads to a decrease in susceptibility to 15%. In the case of PMMA matrices these changes do not exceed the background. The same situation is present for the pure BIBO and low-doped Tm materials. The effect is maximal for a low concentration of Tm - about 0.75%. In the case of bulk glasses the intensity dependences of the second-harmonic generation unambiguously show that the achieved maximal values of second-order susceptibilities do not exceed 3 pm V^-1 for 0.5% Tm concentration.