Picosecond study of near-band-gap nonlinearities in GaInAsP.

From picosecond pump-probe and forward degenerate four-wave mixing (DFWM) experiments, we obtain the near-band-gap nonlinear absorption and refraction properties of GaInAsP for 1.5micron radiation. Using a mode-locked color center laser, the nonlinear signals are studied in room temperature samples as a function of time wavelength for different pump energies. Nonlinear absorption cross-sections (sigma)(eh) as large as 5.7x10(-15) cm(2) are obtained from the pump-probe results, while effective nonlinear cross-sections (sigma)(eff) as large as 9x10(-16) cm(2) (corresponding to a steady state |x(3)|~4.4x10(-3) e.s.u. for a 20 nsec relaxation time) are measured in the DFWM experiments.