The photoinduced magneto-optical Kerr effect during the excitation by picosecond laser pulses is investigated in $\text{CdTe}/{\text{Cd}}_{0.78}{\text{Mg}}_{0.22}\text{Te}$ quantum wells in the spectral range of heavy-hole exciton and trion transitions. Using polarization pulse shaping we were able to generate circularly polarized laser fields with an independent control of temporal and spectral resolution. Changing the frequency and temporal position of the circularly polarized field we show that “off-resonant” optical transitions have a considerable influence on the ultrafast dynamics of the magneto-optical Kerr effect. An excitation of a heavy-hole-exciton with an off-resonant circularly polarized field results in a spin polarization of the electrons in the excited state. Such an “off-resonantly” excited spin population is present only during the action of the laser pulse, but quantum interference of off-resonant and “on-resonant” components leads to beats of the spin population of the excited state and similar beats of the magneto-optical signal with frequency and amplitude determined by the shape of the pump pulse.

• Received 18 March 2009

DOI:https://doi.org/10.1103/PhysRevB.80.235326