Nonlinear optical waveguide spectroscopy of a conjugated polymer: poly(p-phenylenevinylene)

We have measured intensity-dependent prism coupling of poly(p-phenyleneviny lene) thin films with picosecond laser pulses in the range 750-1600 nm. We developed a refined evaluation method that yields the signs and absolute va lues of the nonlinear refractive index nz and the nonlinear absorption coef ficient alpha(2). Strong two-photon absorption levels were found at 2.8 and 3.1 eV. We observed a resonance at 1.3 eV that behaves as saturable absorp tion, and several additional resonances and sign changes of n(2) at even lo wer photon energies. We demonstrate reversible refractive-index changes Del ta(n) = +0.002 at 910-950 nm on a picosecond time scale. Even larger Delta n appear feasible. (C) 1999 Optical Society of America [S0740-3224(99)03011 -8].