Fast relaxing absorptive nonlinear refraction in superlattices

Two nonlinear optical processes in superlattices are studied. The first involves free-carrier absorption and the second involves direct intersubband absorption. The optical field modulates the energy-dependent effective mass or the distribution of electrons among the subbands, giving rise to nonlinear refraction. These processes have picosecond relaxation times and nonlinearities up to four orders of magnitude larger than the nonlinear refractive effects in bulk crystals with comparable relaxation times.