Femtosecond measurements of the nonlinear optical response of telecommunication fiber materials

Summary form only given. A simple and reliable means of determining the nonlinearities of optical fiber materials is needed. The ability to measure fiber precursor materials without the difficulty of pulling a fiber would be especially valuable. We present data on the nonlinear response of fused silica and four mixed silicate/germanate glasses used in telecommunication fibers. The response functions were measured by spectrally resolved two-beam coupling (SRTBC). SRTBC uses a standard pump-probe setup, with the addition of a monochromator to spectrally resolve the probe pulse after the nonlinear interaction. Combined with ultrashort pulses, this simple experiment provides both excellent sensitivity and femtosecond time-resolution, as exemplified by our measurement of fused silica, one of the least nonlinear optical materials. The data were obtained with 17-fs pulses directly from a mode-locked Ti:sapphire laser producing 450 mW output power at /spl sim/800 nm. The intensity at the sample was /spl sim/20 GW/cm/sup 2/. The electronic and nuclear contributions to the optical nonlinearity are clearly resolved. The SRTBC signal is derivative-like, so the nonlinear phase shift due to the electronic Kerr nonlinearity appears as a bimodal signal.