Wavelength Dependence of the Complex Third-Order Nonlinear Optical Susceptibility of Poly(3-hexylthiophene) Studied by Femtosecond Z‑Scan in Solution and Thin Film

• Published in: Journal of physical chemistry. C Vol. 117; no. 49; pp. 26197 - 26203
• Main Authors: Szeremeta, Janusz, Kolkowski, Radoslaw, Nyk, Marcin, Samoc, Marek
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 12-12-2013
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Physics; Red shift; Stacking sequence; Multi-photon processes; Negative refraction; Spectral line shift; Z scan; Nonlinear optical susceptibility; Thin films; Thiophene derivative polymer; Three-photon spectra; Two-photon processes; Non linear effect; Cross sections
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp4051484

Comprehensive studies of the third-order susceptibility of regioregular poly(3-hexylthiophene) in the wavelength range from 530 to 1600 nm for both thin film (with stacked chains interactions) and dilute solution (no chains interactions) were performed with the Z-scan technique. Negative nonlinear refraction was observed in the whole wavelength range of the measurements. The nonlinear absorption exhibits regions of two-photon and three-photon absorption, and on approaching the linear absorption region, a saturable absorption process is seen. It was found that for thin film the effective multiphoton absorption cross-sections σ2 and σ3 are 1.5 and 3 times bigger than for solution, respectively. Influence of the elongated conjugation length in the stacked polythiophene chains in thin film on the red shift of the multiphoton absorption cross-section spectra in comparison with those for polythiophene in solution is discussed.