Polarization-resolved Reflection Research Articles

Dichroic reflection of InAs∕GaAs quantum dots

Polarization-resolved reflection measurements are performed on nearly circular InAs∕GaAs quantum dots (QDs) by means of time-resolved differential reflection spectroscopy. We observe linear polarization anisotropy of the differential absorption, revealing the dichroic character of the QD reflection. The observed magnitude of the dichroism is Θ[11¯0]∕Θ[110]=1.07. The polarization has a preferential direction orientated along the [11¯0] crystal axis, which is confirmed by polarization-resolved photoluminescence. We observe that the polarization anisotropy of the reflectivity is strongly dependent on the pump excitation density, decreasing from ρ=0.14 at low excitation to ρ=0.06 at high excitation. The pump power dependence is described by a binomial model taking into account the statistics of carrier capture into a limited number of QDs.

Magnetic field controlled in‐plane optical anisotropy in parabolic (Cd,Mn,Mg)Te quantum wells

In-plane optical anisotropy was measured in polarization-resolved reflectivity experiments on a CdTe-based multiple quantum well sample. Parabolic confining potentials were achieved by introduction of controlled Mg mole fraction. Addition of 6 molar % of Mn across the sample structure allowed us to control the light – heavy hole splitting by giant Zeeman effect. We observed an enhancement of the measured anisotropy when the light- and heavy hole bands were brought together by the magnetic field. A model calculation produced a phenomenological description of the observed behavior. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fine tuning of the dichroic behavior of Bragg reflectors based on anisotropically nanostructured silicon

Electro-chemical etching of heavily doped, (110) oriented, p+ (boron) doped silicon wafers results in porous silicon (PSi) layers which exhibit a strong in-plane anisotropy of the refractive index (birefringence). Single- and multiple layers of anisotropically nanostructured silicon (Si) have been fabricated and studied by polarization-resolved reflection and transmission measurements. Dielectric stacks of birefringent PSi acting as distributed Bragg reflectors have two distinct reflection bands depending on the polarization of the incident linearly polarized light. This effect is caused by a three-dimensional (in plane and in-depth) variation of the refraction index. The possibility of fine tuning the two orthogonally polarized reflection bands and their spectral splitting is demonstrated.

Dichroic behavior of multilayer structures based on anisotropically nanostructured silicon

Multilayer structures of anisotropically nanostructured (birefringent) silicon have been fabricated and studied by polarization-resolved reflection and transmission measurements. We demonstrate that stacks of birefringent porous silicon layers with alternating refractive indices and thicknesses act as dichroic Bragg reflectors or dichroic microcavities with a transmission/reflection dependent on the polarization direction of the incident light. The possibility of separate fine tuning of two orthogonally polarized transmission/reflection bands and their spectral splitting is demonstrated.

Dichroic Bragg reflectors based on birefringent porous silicon

Multilayers of anisotropically nanostructured silicon (Si) have been fabricated and studied by polarization-resolved reflection measurements. Alternating layers having different refractive indices exhibit additionally a strong in-plane anisotropy of their refractive index (birefringence). Therefore, a stack of layers, acting as a distributed Bragg reflector, has two distinct reflection bands, depending on the polarization of the incident linearly polarized light. This effect is governed by a three-dimensional (in-plane and in-depth) variation of the refractive index. These structures can yield optical effects which are difficult to achieve with conventional Bragg reflectors.

Multiple Bragg wave coupling in photonic band-gap crystals

We report angle and polarization resolved reflectivity from strongly photonic fcc crystals consisting of air spheres in titania. For a $30\ifmmode^\circ\else\textdegree\fi{}$ range of angles of incidence, multiple peaks with distinct polarization dependence are observed that clearly reveal avoided crossing behavior. Calculated photonic dispersion curves show that the multiple peaks result from band repulsion of Bloch states due to simultaneous Bragg diffraction by (111) and (200) planes. Our results demonstrate that many-wave coupling leads to substantial deviations from simple Bragg diffraction, with significantly flattened bands, a requirement for the appearance of complete photonic band gaps.

Measurement and simulation of anisotropy in the infrared and Raman spectra of Β-FeSi2single crystals

In this paper we show that the orthorhombic phase of ${\mathrm{FeSi}}_{2}$ (stable at room temperature) displays a sizable anisotropy in the infrared spectra, with minor effects in the Raman data too. This fact is not trivial at all, since the crystal structure corresponds to a moderate distortion of the fluorite symmetry. Our analysis is carried out on small single crystals grown by flux transport, through polarization-resolved far-infrared reflectivity and Raman measurements. Their interpretation has been obtained by means of the simulated spectra with tight-binding molecular dynamics.