. (2016) Ultrafast changes of magnetic anisotropy driven by laser-generated coherent and noncoherent phonons in metallic films. Physical Review B, 93 (21 A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. ABSTRACTUltrafast optical excitation of a metal ferromagnetic film results in a modification of the magnetocrystalline anisotropy and induces the magnetization precession. We consider two main contributions to these processes: an effect of non-coherent phonons, which modifies the temperature dependent parameters of the magneto-crystalline anisotropy; and coherent phonons in the form of a strain contributing via inverse magnetostriction. Contrary to the earlier experiments with high symmetry ferromagnetic structures, where these mechanisms could not be separated, we study the magnetization response to femtosecond optical pulses in the low-symmetry magnetostrictive Galfenol film so that it is possible to separate the coherent and non-coherent phonon contributions. By choosing certain experimental geometry and external magnetic field, we can distinguish the contribution from a specific mechanism. Theoretical analysis and numerical calculations are used to support the experimental observations and proposed model.

We report on the photoluminescence characterization of GaAs quantum dots embedded into AlGaAs nanowires. Time integrated and time resolved photoluminescence measurements from both an array and a single quantum dot/nano-wire are reported. The influence of the diameter sizes distribution is evidenced in the optical spectroscopy data together with the presence of various crystalline phases in the AlGaAs nanowires.

We report on the observation of optical activity of quantum wells resulting in the conversion of the light polarization state controlled by the light propagation direction. The polarization conversion is detected in reflection measurements. We show that a pure s-polarized light incident on a quantum well is reflected as an elliptically polarized wave. The signal is drastically enhanced in the vicinity of the light-hole exciton resonance. We show that the polarization conversion is caused by the spin-orbit splitting of the light hole states and the birefringence of the studied structure. The bulk inversion asymmetry constant β h ≈ 0.14 eVÅ is determined for the ground light hole subband in a 10 nm ZnSe/ZnMgSSe quantum well. PACS numbers: 73.21.Fg, 78.20.Ek, 42.25.Ja Studies of polarization-sensitive optical effects allow creating optical devices and give access to fundamental properties of material systems. A very important effect intensively investigated and widely used in practice is a conversion of light polarization state [1,2]. Examples are the rotation of a linear polarization plane and the transformation of a pure linearly or circularly polarized wave into an elliptically polarized light. A possibility for the polarization conversion exists in systems of sufficiently low spatial symmetry. For example, birefringent media effectively rotate light polarization plane and produce light helicity. Basic examples are half-and quarter-wave plates made of birefringent crystals widely used in both laboratories and in industry. Recently, polarization conversion has been observed in metamaterials [2][3][4], twisted photonic crystal fibers [5] and microcavities [6]. While metamaterials convert light polarization due to a special design of building blocks, semiconductor nanostructures are birefringent as-grown. The polarization conversion has been demonstrated in a number of experiments on quantum wells (QWs) [7][8][9][10][11] and quantum dots [12,13]. The low symmetry of QWs can be caused by in-plane deformations [8][9][10] or by microscopic structure of interfaces [14,15], while the birefringence of self-assembled quantum dots appears due to their anisotropic shape [13].

We report on a numerical model of quasi onedimensional and quasi zero-dimensional semiconductor heterostructures. This model is strictly based on experimental structures of cylindrical nanocolumns of AlGaAs grown by molecular-beam epitaxy in the (111) direction. The nanocolumns are of 20-50 nm in diameter and 0.5-1 µm in length and contain a single GaAs quantum dot, of 2 nm in thickness and 15-45 nm in diameter. Since the crystal phase of these nanowires spontaneously switches during the growth from zincblende to wurzite structures we implement a continuum elastic model and 8 band k • p model for polymorph crystal structures. The model is used to compute electromechanical fields, wave-function energies of the confined states and optical transitions. The model compares a pure zincblende structure with a polymorph in which the zincblende disk of GaAs is surrounded by wurtzite barriers and results are compared to experimental photoluminescence excitation spectra. The good agreement found between theory and features in the spectra supports the polyphorm model.