We show that the magnetization of a thin ferromagnetic (Ga,Mn)As layer can be modulated by picosecond acoustic pulses. In this approach a picosecond strain pulse injected into the structure induces a tilt of the magnetization vector $\mathbf{M}$, followed by the precession of $\mathbf{M}$ around its equilibrium orientation. This effect can be understood in terms of changes in magnetocrystalline anisotropy induced by the pulse. A model where only one anisotropy constant is affected by the strain pulse provides a good description of the observed time-dependent response.

We present the first experimental investigation of ultrafast optical switching in a three-dimensional photonic crystal made of a Si-opal composite. Ultrafast (30 fs) changes in reflectivity around the photonic stop band up to 1% were measured for moderate pump power $(70\mu \mathrm{J}/{\mathrm{c}\mathrm{m}}^2)$. Short-lived photoexcited carriers in silicon induce changes in the dielectric constant of Si and diminish the constructive interference inside the photonic crystal. The results are analyzed within a model based on a two-band mixing formalism.

The bias voltage applied to a weakly coupled $n$-doped GaAs/AlAs superlattice increases the amplitude of the coherent hypersound oscillations generated by a femtosecond optical pulse. This bias-induced amplitude increase and experimentally observed spectral narrowing of the superlattice phonon mode with a frequency 441 GHz provides the evidence for hypersound amplification by stimulated emission of phonons in a system where the inversion of the electron populations for phonon-assisted transitions exists.

Using the photoluminescence of the trion feature as a monitor, we study experimentally the spin relaxation of the hole in self-assembled CdSe/ZnSe quantum dots. We observe two kinds of depolarization. The first one is due to an imperfect spin imprint of the circular photon polarization. The second transient depolarization is caused by the hole spin-flip in the Kramers degenerate trion doublet. At low temperature, the spin relaxation exhibits a slow component with a time constant longer than 10 ns. A considerable speedup takes place at higher temperature, reaching the sub nanosecond range at about 70 K. The activation energy is consistent with LO phonons.

The elastic coupling between the $a\mathrm{\text{−}}{\mathrm{SiO}}_2$ spheres composing opal films brings forth three-dimensional periodic structures which besides a photonic stop band are predicted to also exhibit complete phononic band gaps. The influence of elastic crystal vibrations on the photonic band structure has been studied by injection of coherent hypersonic wave packets generated in a metal transducer by subpicosecond laser pulses. These studies show that light with energies close to the photonic band gap can be efficiently modulated by hypersonic waves.