Picosecond degenerate four-wave mixing study of nonlinear optical properties of the poly-N-vinyl carbazole: 2,4,7-trinitrofluorenone composite polymer photoconductor

Resonant third-order nonlinear optical susceptibility χ⁽¹³⁾ of poly-N-vinyl carbazole: 2,4,7-trinitrofluorenone composite polymer photoconductor has been measured at 602 nm for various compositions by picosecond degenerate four-wave mixing. The origin of effective third-order nonlinearity of this system is attributed to the charge-transfer excitation which creates thermalized correlated electron-hole pairs. The optical nonlinearity of this polymeric system is characterized by a long relaxation time of hundreds of picoseconds. A progressive enhancement of the signal intensity and hence effective χ₍₃₎ accompanied by an increase in the decay rate of the degenerate four-wave mixing signal has been observed with an increase in the mole fraction of trinitrofluorenone.