Electric and magnetic dipole two-photon absorption in semiconductors

Nonlinear spectroscopy of the exciton fine structure in GaAs has allowed us to measure simultaneously both magnetic dipole two-photon absorption and electric dipole one-photon absorption. The splitting of the excitonic ground state into the spin-allowed orthoexciton and the spin-forbidden paraexciton gives the electron-hole exchange energy directly. The peak assignment is proved by nonlinear magnetoabsorption. Utilizing electric dipole two-photon magnetoabsorption within the same experiment, a rich fine structure of the 2P exciton has been observed that has not been previously resolved. © 1996 The American Physical Society.