Compact strain-sensitive flexible photonic crystals for sensors

A promising fabrication route to produce absorbing flexible photonic crystals is presented, which exploits self-assembly during the shear processing of multi-shelled polymer spheres. When absorbing material is incorporated in the interstitial space surrounding high-refractive-index spheres, a dramatic enhancement in the transmission edge on the short-wavelength side of the band gap is observed. This effect originates from the shifting optical field spatial distribution as the incident wavelength is tuned around the band gap, and results in a contrast up to 100 times better than similar but nonabsorbing photonic crystals. An order-of-magnitude improvement in strain sensitivity is shown, suggesting the use of these thin films in photonic sensors

Fabrication of micromirrors with pyramidal shape using anisotropic etching of silicon

Gold micro-mirrors have been formed in silicon in an inverted pyramidal shape. The pyramidal structures are created in the (100) surface of a silicon wafer by anisotropic etching in potassium hydroxide. High quality micro-mirrors are then formed by sputtering gold onto the smooth silicon (111) faces of the pyramids. These mirrors show great promise as high quality optical devices suitable for integration into MOEMS systems

Anisotropic nanostructures directly written by fs pulses in wide-bandgap materials

The use of lasers to directly pattern optoelectronic devices primarily utilizes direct irradiation by UV light. We present here an alternative route using multi-photon absorption within a spherical focus in 3D space, thus allowing complex embedded structures to be directly written. In wide-bandgap materials such as chalcogenide, fluoride and silica glasses, our observations suggest free electrons are produced within the focus of a high-power infrared ultrashort pulse. The anisotropic interaction of this plasma with the incident pulse produces micron-sized DBR gratings of a 150nm pitch. An amplified Ti:S laser with 250kHz repetition rate, 150fs pulse duration, and wavelength tuned from 800-850nml is used to write embedded diffraction gratings and arrays of dots. The laser beam is focussed with a 50x objective into transparent polished samples, with pulse energies ranging from 0.1-1.1pJ (Fig.la). During the writing process broadband sub-bandgap UV light is emitted from a micron-sized spot at the sample focus. The written structures are permanent, typically with large refractive index changes on the order of Delta.n = +0.01 depending on the material

Spin filtering and magnetoresistance in ballistic tunnel junctions

We theoretically investigate magnetoresistance (MR) effects in connection with spin filtering in quantum-coherent transport through tunnel junctions based on non-magnetic/semimagnetic heterostructures. We find that spin filtering in conjunction with the suppression/enhancement of the spin-dependent Fermi seas in semimagnetic contacts gives rise to (i) spin-split kinks in the MR of single barriers and (ii) a robust beating pattern in the MR of double barriers with a semimagnetic well. We believe these are unique signatures for quantum filtering.Comment: Added references + corrected typo

Surface enhanced Raman scattering using metal modified microstructured optical fibre substrates

We report the fabrication of metallic metamaterials using microstructured optical fibres as templates. The resulting fibres serve as excellent substrates for surface enhanced Raman spectroscopy and represent an exciting platform for in-fibre plasmonic devices

Polariton condensation and lasing in optical microcavities - the decoherence driven crossover

We explore the behaviour of a system which consists of a photon mode dipole coupled to a medium of two-level oscillators in a microcavity in the presence of decoherence. We consider two types of decoherence processes which are analogous to magnetic and non-magnetic impurities in superconductors. We study different phases of this system as the decoherence strength and the excitation density is changed. For a low decoherence we obtain a polariton condensate with comparable excitonic and photonic parts at low densities and a BCS-like state with bigger photon component due to the fermionic phase space filling effect at high densities. In both cases there is a large gap in the density of states. As the decoherence is increased the gap is broadened and suppressed, resulting in a gapless condensate and finally a suppression of the coherence in a low density regime and a laser at high density limit. A crossover between these regimes is studied in a self-consistent way analogous to the Abrikosov and Gor'kov theory of gapless superconductivity.Comment: 17 pages, 8 figures, submitted to PR

Exciton Spin Dynamics in Semiconductor Quantum Wells

In this paper we will review Exciton Spin Dynamics in Semiconductor Quantum Wells. The spin properties of excitons in nanostructures are determined by their fine structure. We will mainly focus in this review on GaAs and InGaAs quantum wells which are model systems.Comment: 55 pages, 27 figure

Ultrafast long-range energy transport via light-matter coupling in organic semiconductor films

The formation of exciton-polaritons allows the transport of energy over hundreds of nanometres at velocities up to 10^6 m s^-1 in organic semiconductors films in the absence of external cavity structures