Third-order nonlinear optical properties of thin films of poly(p-phenylene benzobisthiazole) and its molecular composites with polyamides

The nonresonant third-order nonlinear optical properties of thin films of poly(p-phenylene benzobisthiazole) (PBZT) and PBZT/nylon 66 and PBZT/poly(trimethylhexamethylene terephthalmide) (PTMHT) molecular composites have been investigated using picosecond third-harmonic generation at 1.9 μm. The measured χ(3)(−3ω,ω,ω,ω) for the pure PBZT was (1.37±0.27)×10−11 esu. The χ(3) of PBZT/nylon composites showed a linear dependence on composition. In contrast, the χ(3) of PBZT/PTMHT molecular composites significantly deviated from this linear dependence, showing enhanced values. No in-plane anisotropy in any of the films was detected. The optical damage threshold of PBZT was measured to be ≳50 GW/cm2 for 30 ps pulses at 1.9 μm.