Ultrashort dephasing-time measurements in Nile Blue polymer films

Optical dephasing measurements using degenerate four-wave mixing (DFWM) were performed on thin dye-polymer films at room temperature. Incoherent light centered at 575 nm was used as a source for ultrafast measurements on the blue side of the inhomogeneous distribution of the oxazine dye Nile Blue. Under these conditions, a new form of interference was observed as a sinusoidal variation of the DFWM signal versus delay time. A measured interference period of 1.96+/-0.07 fs corresponds to the optical cycle time of the light source. Numerical solutions for the DFWM intensity confirm the oscillation effect and estimate a measured dephasing time of 2-3 fs.