Ultrafast below-resonance Raman rotation of electron spins in GaAs quantum wells

We demonstrate that short optical pulses below the absorption edge of GaAs quantum wells rotate the spin polarization of dopant electrons with negligible excitation of additional carriers. The dopant electrons are partially polarized by a magnetic field perpendicular to the optical axis, and a circularly polarized pump pulse rotates the polarization through an adiabatic Raman process. This rotated spin polarization precesses in the magnetic field out of phase by pi/2 relative to spin-polarized carriers generated by absorption. This technique can be used to manipulate spin polarizations without the complication of optically excited electrons and holes.