Ultrafast third-order nonlinear optical properties of self-assembled poly[[4,4-bis(4-sulphobutyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl]-1,4-phenylene sodium sa multilayer films

Abstract

An ultrathin multilayer film with well-defined structure containing anionic Poly[[4,4-bis(4-sulphobutyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl]-1,4-phenylene sodium sa (PCPDTPhSO3Na) and cationic poly(diallydimethyl ammonium chloride) (PDDA) was prepared using layer-by-layer assembly technique. The growth of the film was monitored by UV–Vis absorption spectroscopy, showing regularly consecutive adsorption. The ultrafast third-order nonlinear optical (NLO) properties of the multilayer film were investigated via the 4f coherent imaging measurement with phase object with 190 fs laser pulses at both 400 and 532 nm. The results demonstrate that PCPDTPhSO3Na/PDDA film exhibited excellent self-focusing effect (n 2 ∼2.42 × 10−16 m2/W) and reverse saturable absorption properties (β ∼6.34 × 10−10 m/W) at 400 nm. In contrast, self-focusing effect (n 2 ∼1.81 × 10−16 m2/W) and saturable absorption properties (β ∼−8.02 × 10−10 m/W) are observed when the laser wavelength (532 nm) is near-resonant with the absorption peak (470 nm). Our studies indicate that the PCPDTPhSO3Na/PDDA film is a promising candidate for applications in NLO devices.