The third-order nonlinear properties of new composite materials obtained by embedding a new type π-conjugated copolymer [4,4-diazobenzene-2,5-thiophene](PDABTh) in porous silicon(PS) are measured by means of the reflection Z-scan technique under 532 nm.The picosecond measurements show a significant increase of nonlinear refractive index of composite materials respect to the porous silicon.The special π-electron structure of PDABTh may contribute to these relatively large nonlinear optical proper...