Abstract

Recently, the source of the optical nonlinearities near the band edge in bulk GaAs has been the subject of much study. At high density, it is well known that phase- space filling and screening dominate. At moderate densities, excitation-induced dephasing (EID) becomes a major source of nonlinearity.¹ The role of the biexciton has also been suggested by recent data.² We find, however, that below exciton densities of about 3 × 10¹⁴ cm⁻³ a well-defined transition from behavior dominated by EID to a completely different nonlinear response characterized by induced absorption, spin- dependent interactions, and an excitation- induced line narrowing (EIN) is observed. The data suggest a multiphoton nonlinear response and may indicate collective effects.

© 1995 Optical Society of America