Picosecond pump-probe interferometric measurement of optical nonlinearity in semiconductor-doped fibers

Refractive and absorptive optical nonlinearity can be distinguished using a pump-probe interferometric technique with picosecond time resolution. The method is applied to both resonant and nonresonant nonlinearities in optical fibers and reveals marked differences between the relaxation behavior of the refractive and absorptive nonlinearity in certain cases. A monomode fiber doped with CdS(x)Se(1-x) semiconductor nanocrystals exhibits a large optically induced phase shift with ~10-psec relaxation time, which is many orders faster than the relaxation of the absorptive nonlinearity under identical conditions.