Poly(indenofluorene) shows a strong degenerate four-wave mixing (DFWM) response when it is excited with 100-fs pulses at 800 nm. The DFWM signal scales with the 1.5 power of the input intensity, which we interpret as being due to absorption saturation phenomena. The saturation was studied by open-aperture Z scan in dilute solutions of poly(indenofluorene) in chloroform. The changes in the absorption coefficient α are described by the formula <i>α</i> = <i>α</i><sub>0</sub>/[1 + (<i>I</i>/<i>I</i><sub>sat</sub>)<sup>1/2</sup>], where <i>I</i><sub>sat</sub> is the saturation intensity, which is found to be of the order of 100>MW/cm<sup>2</sup>.
© 1998 Optical Society of America
Marek Samoc, Anna Samoc, Barry Luther-Davies, Helge Reisch, and Ullrich Scherf, "Saturable absorption in poly(indenofluorene): a picket-fence polymer," Opt. Lett. 23, 1295-1297 (1998)