| Ultrafast measurement of dilute magnetic semiconductors has been intense over the last decade due to applications in spintronics. This thesis describes the use of optical measurements, both spontaneous scattering and impulsive stimulated scattering, to study two dilute magnetic semiconductors.;In the (Cd,Mn)Te system, two sets of experiments are presented here. In this system, Mn acts as a column 2 alloy, allowing the growth of high quality magnetic semiconductors. Using a spatial light modulator to create shaped pulses, we demonstrate coherent control of entangled bound electrons in this material system. First, we demonstrate the capabilities of such a system by coherently controlling the charge density modes in a GaAs quantum well. Then, the same technique is applied to a CdMnTe quantum well with electrons bound to unintentional donors. A pair of pulses is constructed to provide ideal destruction of the signal from a single bound electron spin flip, leaving the signal for the double spin flip. Additional data demonstrates the linear nature of the pump-probe signal of the single and double spin flip.;The second set of experiments presented here in (Cd,Mn)Te involve studying the decay of the collective spin flip wave in a 2DEG formed in a high quality CdMnTe quantum well. The collective spin wave mode is observed in pump-probe measurement data. Pump-probe measurements demonstrate the effects of spin polarization, heating, and carrier population on the lifetime of the spin wave. A decrease in spin polarization due to lower Mn concentration or lower magnetic field decreases the lifetime of the spin flip wave. The temperature of the sample is measured by fitting the frequency of the spin flip wave to the Brillouin function. The spin wave lifetime rapidly decreases with small amounts of laser heating. Additionally, multiple temperature zones due to laser heating are observed with sufficient laser pump power. Carriers injected with the laser energy above the absorption edge decrease the lifetime.;The semiconductor system (Ga,Mn)As has been one of the most studied dilute magnetic semiconductors due to the advanced state of GaAs growth and fabrication technology. In this system, ferromagnetic behavior between the Mn atoms is mediated by hole carriers. As a substitutional alloy replacing Ga, Mn acts as an acceptor, creating the holes necessary for ferromagnetism. However, Mn is not an ideal acceptor, and at low temperatures holes become bound to the Mn acceptors. In heavily doped, ferromagnetic GaMnAs, paramagnetic regions persist containing holes bound to Mn acceptors. Previously, transitions between bound hole states were studied using inelastic scattering. In this work, the selection rules observed are determined to be the result of the relative spin populations of the Zeeman split spin states. A second set of pump-probe experiments performed on thin GaMnAs layers show that the highly interface-dependent magnon modes depend strongly on the As source used during growth. |
