Ultrafast pump-probe magneto-optical spectroscopy is used to study coherent spin dynamics in ferromagnetic semiconductor Ga 1−x Mn x As systems at excitation photon energies E ph both above and below the band gap E g of GaAs. Above E g , the temporal Kerr rotation signal is found to be strongly dependent on pump photon polarization. This polarization dependence, persisting to room temperature, is attributed to spins of electrons photoexcited to the conduction band, and disappears for E ph Ͻ E g . Below the Curie temperature T C of the Ga 1−x Mn x As samples, the temporal Kerr rotation acquires an additional oscillatory component with a period of the order of 100 ps, attributed to the precession of the ferromagnetically coupled Mn spins. This precession is observed for excitation both above and below E g , regardless of the pump polarization states. The detailed characteristics of this ferromagnetic precession are discussed in terms of the Landau-Lifshitz-Gilbert model. In discussing the observed results, special attention is given to the process of the magnetization precession due to excitation of the pump, to its dependence on the pump intensity, and ambient temperature, and to the relationship between the damping of the magnetization precession and the defects characteristic of ferromagnetic GaMnAs.

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We report the results of coherent acoustic phonon spectroscopy analysis of band-edge optical modification of GaAs irradiated with 400 keV Ne++ for doses between 1011–1013 cm−2. We relate this optical modification to the structural damage density as predicted by simulation and verified by ion channeling analysis. Crystal damage is observed to cause optical modification that reduces the amplitude of the optoacoustic signal. The depth-dependent nature of the optoacoustic measurement allows us to determine optical damage cross-sections along the ion track, which are found to vary as a function of position along the track. Unexpectedly, we find that this optical modification is primarily dependent on the structural damage density and insensitive to the specific defect configuration along the ion track, suggesting that a simple model of defect density along the track is sufficient to characterize the observed optical changes. The extent of optical modification is strongly probe frequency-dependent as the frequency is detuned from the GaAs band edge. As determined from the experimental measurements, the spatial extent of optical modification exceeds the spatial extent of the structural disorder by an order of magnitude.

Single-crystal CVD diamond specimens were implanted with 1-MeV He+ ions at fluences ranging from 1014 to 1016 cm−2 and analyzed using coherent acoustic phonon spectroscopy. The coherent acoustic phonon response varies greatly with implantation fluence and provides depth-dependent information about the implantation defect-induced modification of diamond's optical characteristics. The results indicate an increase in the real and imaginary refractive index, as well as a sign reversal of the photoelastic coefficients at higher levels of implantation damage. These studies provide insight into the application of ion implantation to the fabrication of diamond-based photonic devices.

Erbium (Er)-doped ZnO thin films were grown on fused silica (SiO 2 ) substrates by pulsed electron-beam deposition (PED) and analysed by Rutherford backscattering spectrometry (RBS), ultraviolet-visible absorption, and photoluminescence (PL). Subsequent annealing at 700 • C produces remarkable effects on the optical properties of Er-doped films. Under 325 nm excitation, a dramatic increase of deep-level emission from 450 to 680 nm was observed from annealed Er-doped ZnO films. Under 488 nm excitation, the PL spectrum of annealed Er-doped ZnO films revealed sharp and well-resolved Stark-splitting peaks in both the green emission of 4 S 3/2 → 4 I 15/2 transition and the red emission of 4 F 9/2 → 4 I 15/2 transition of Er 3+ ions, which suggests that the Er ions have been incorporated inside the crystalline ZnO grains after thermal annealing.