Time-resolved Kerr (Faraday) rotation experiments allow for the observation of polariton spin beats in both InGaAs and CdMnTe quantum well (QW) microcavities. The existence of these beats is an unambiguous manifestation of the coherent energy exchange between exciton and photon components of polariton states created by a circularly polarized and spectrally wide femtosecond laser pulse. The polariton states are also shown to be split into a linearly polarized doublet. This splitting is responsible for the polarization transfer between linearly and circularly polarized states. In a highest quality sample the resulting spin dynamics could be detected.

Linear dichroism experiments show that exciton-polariton ground states are split into a linearly polarized doublet. At normal incidence and zero detuning this splitting does not exceed 10 mu eV for the upper polariton branch and 3 mu eV for the lower one. For both branches the splitting decreases with positive and negative detuning. (c) 2007 Elsevier Ltd. All rights reserved.

A diluted magnetic semiconductor (DMS) quantum well (QW) microcavity operating in the limit of the strong coupling regime is studied by magnetoptical experiments. The interest of DMS QW relies on the possibility to vary the excitonic, resonance over a wide range of energies by applying an external magnetic field, typically about 30 meV for 5 T in our sample. In particular, the anticrossing between the QW exciton and the cavity mode can be tuned by the external field. We observe the anticrossing and formation of exciton polaritons in magneto-reflectivity experiments. In contrast, magneto-luminescence exhibits purely excitonic character. Under resonant excitation conditions an additional emission line is observed at the energy of the dark exciton. The creation of dark excitons is made possible due to heavy hole-light hole mixing in the QW. The emission at this energy could be due to a combined spin flip of an electron and a bright exciton recombination. (c) 2007 Elsevier Ltd. All rights reserved.

Optically induced nuclear spin polarization is studied via time-resolved magnetooptical Kerr effect in Voigt configuration in n-doped InP. The hyperfine field acting on electrons is detected via a phase shift of the electron spin precession. The dependence of the hyperfine field on external field and the polarization time of the nuclei are discussed within a simple model neglecting nuclear spin diffusion.

Exciton and polariton spin beats are observed in a CdMnTe quantum well embedded in a microcavity using time-resolved Kerr rotation experiments under magnetic field. Photoinduced linear birefiringence phenomenon allows to comprehend the polariton spin beats using linear polarized pumping in Faraday geometry. Exciton spin beats can be detected in the standard configuration with circularly polarized pump pulse and under in-plane magnetic field.

In semiconductors optically enhanced polarization of nuclei is known to be primarily due to photoexcited electrons. We show that holes play a role in this process via the spin-dependent recombination of the carriers. Our results are obtained in n-type InP where spin-dependent recombination leads to the inversion of the nuclear field direction due to the donor spins cooling under optical excitation.