Ultrafast dynamics of carriers and nonlinear refractive index in bulk polycrystalline diamond.

The free-carrier dynamics and nonlinear refractive index in bulk polycrystalline diamond are investigated using a femtosecond ultraviolet-pump-optical-probe technique with a phase object. Normalized transmittances under open-aperture and closed-aperture conditions are simultaneously measured to determine the dynamics of nonlinear absorption and refraction in the sample. In the dynamics of nonlinear absorption, three processes are clearly observed: nondegenerate two-photon absorption, fast and slower decay components of the free-carrier dynamics. The lifetimes of the free carriers are precisely measured. In the dynamics of nonlinear refraction, we obtain the nonlinear refractive coefficient and find that the results obtained under the femtosecond regime differ from those of other semiconducting materials previously measured under the picosecond regime. [ABSTRACT FROM AUTHOR]