High-efficiency harmonic generation is observed in a semiconducting polymer RR-P3HT [regioregular poly(3-hexylthiophene)], which exhibits a high nonlinear susceptibility [χ ⁽²⁾ > 10⁻⁶ m V⁻¹] under pumping by a pulsed fibre laser. The harmonic generation efficiency in RR-P3HT is comparable or higher than that observed for liquid crystals, which are used in reference experiments to estimate the susceptibility [the quadratic susceptibility of a nematic liquid crystal NLC 1289 is χ ⁽²⁾ ≈ 2 10⁻⁶ m V⁻¹]. No generation is observed in polythiophene with a random structure, RRa-P3HT [regiorandom poly(3-hexylthiophene)], at the same pump power. It is experimentally demonstrated that a necessary condition for generating the second and third harmonics in a polymer, along with a high pump power density, is the presence of a large power density gradient (exceeding 10¹³ W m⁻³). Based on a preliminary theoretical analysis, we can suggest that the quadrupole mechanism, which is a consequence of the regularity of RR-P3HT structure in the thin near-wall layer, may contribute significantly to the nonlinear radiation conversion in semiconducting polymers.

在半导体聚合物 RR-P3HT [区域规则聚（3-己基噻吩）] 中观察到高效谐波产生，其在脉冲光纤泵浦下表现出高非线性磁化率 [ χ ⁽²⁾ > 10 ^-6 m V ^-1 ]激光。RR-P3HT 中的谐波产生效率与观察到的液晶相当或更高，在参考实验中用于估计磁化率 [向列液晶 NLC 1289 的二次磁化率是χ ⁽²⁾ ≈ 2 10 ^-6毫伏^-1]。在相同泵浦功率下，在具有随机结构的聚噻吩 RRa-P3HT [区域随机聚（3-己基噻吩）] 中未观察到生成。实验证明，在聚合物中产生二次和三次谐波以及高泵浦功率密度的必要条件是存在大功率密度梯度（超过10 ¹³ W m ^-3）。基于初步的理论分析，我们可以认为四极机制是近壁薄层中 RR-P3HT 结构规律的结果，可能对半导体聚合物中的非线性辐射转换有显着贡献。