Volume 91, Issue 17, 22 October 2007
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
We report a plasmonicquantum cascade laserantenna that confines coherent midinfrared radiation well below the diffraction limit. The antenna was fabricated on the facet of a midinfrared quantum cascade laser and consists of a pair of goldnanorods separated by a gap. The antenna near field was characterized by an apertureless near-field scanning optical microscope; field confinement of about 100 and , limited by the gap size, was demonstrated at wavelengths of 7.0 and , respectively. This device may find important applications in midinfrared subwavelength chemical and biological imaging and spectroscopy.
- LASERS, OPTICS, AND OPTOELECTRONICS
Controlling enhanced transmission through metallic gratings with subwavelength slits by anisotropic waveguide resonance91(2007); http://dx.doi.org/10.1063/1.2800802View Description Hide Description
We propose an analytically tractable structure for controlling enhanced transmission through a metallic grating with subwavelength slits by filling the slits with an anisotropicmaterial such as a liquid crystal. As the director rotates, the Fabry-Pérot condition is modified and the transmission peaks shift. Analytical results of a single-mode theory for the propagation constant, transmission efficiency, and the tunable range of peak wavelengths are given, taking the finite conductivity of metal into account. Analytical results are in good agreement with those calculated by the rigorous coupled-wave analysis, indicating that waveguide resonance plays a dominant role and the results are scalable.
Experimental transfer of torque induced by localized polarization of radially polarized vector beams to anisotropic microparticles91(2007); http://dx.doi.org/10.1063/1.2795334View Description Hide Description
Polarization-induced torque of a radially polarized beam is investigated on anisotropic micro-particles. Radially polarized beams possess full cylindrical symmetry; therefore, any line drawn from the beam axis to the circumference contains identical polarization vectors, acting locally as linearly polarized. It is experimentally observed that anisotropic microparticles experience an aligning torque by the localized segment of the radially polarized beam, setting it to rotate around the beam axis. The rotation of the particle thus enables the mapping of the localized electric vector distribution of radially polarized beams.
91(2007); http://dx.doi.org/10.1063/1.2802067View Description Hide Description
The authors demonstrate the coupling effects between the quantum well(QW) and surface plasmon (SP) generated nearby on the -type side in an single-QW light-emitting diode(LED). The QW-SP coupling leads to the enhancement of the electroluminescence(EL) intensity in the LED sample designed for QW-SP coupling and reduced SP energy leakage, when compared to a LED sample of weak QW-SP coupling or significant SP energy loss. In the LED samples of significant QW-SP coupling, the blueshifts of the photoluminescence and ELemission spectra are observed, indicating one of the important features of such a coupling process. The device performance can be improved by using the -type side for SP generation such that the device resistance can be reduced and the QW-SP coupling effect can be enhanced (by further decreasing the distance between the QW and metal) because of the higher carrier concentration in the -type layer.
91(2007); http://dx.doi.org/10.1063/1.2800374View Description Hide Description
By using a rigorous diffraction theory, the localization of light near textured zinc oxide (ZnO)surfaces is theoretically investigated and compared with experimental data obtained from scanning-near-field-optical microscopy. Although random by nature, these surfaces show well-defined geometrical features, which cause the formation of localized light patterns near the surface. Particularly, photon jets are observed to emerge from conical surface structures. Because these structures are of primary importance for applications in photovoltaics, we analyze the “real” surface topography of texturedZnO used in silicon solar cells. With this work, valuable insight is provided into the mechanism of light coupling through randomly textured interfaces.
91(2007); http://dx.doi.org/10.1063/1.2798505View Description Hide Description
The phase lens, also called kinoform, a promising focusing component in an integrated micro-optical system, was produced by femtosecond laserfabrication via two-photon photopolymerization. Kinoforms consisting of two-, four-, eight-level subzones with level thicknesses of 475, 238, and demonstrate diffraction efficiencies of 30%, 54%, and 68%, respectively, which are comparable with the theoretical limit and with those from the commercial phase lenses. In addition, a reflective diffractive micromirror was proposed and realized with the aid of electroless plating. These works show the promising prospect of femtosecond laserfabrication in manufacturing optical micronanodevices and their integrated system with optical quality.
91(2007); http://dx.doi.org/10.1063/1.2799163View Description Hide Description
We show that laser filamentation can be initiated and propagate through strong extended turbulence well above the typical atmospheric values. We suggest that the effect of turbulence on filamentation is characterized by the product of the structure parameter for the refractive index and the length of the turbulence region. Half of the filaments are transmitted for . Moreover, the surviving filaments keep their key spectral properties including correlations inside the white-light continuum.
91(2007); http://dx.doi.org/10.1063/1.2799179View Description Hide Description
The results of studies of one-dimensional Bragg structures (one-dimensional periodic lattice) with localized defects are presented. The defects considered are localized, step changes (shifts) of the lattice phase (corrugation). The influence of the defects on the periodic lattice band-gap parameters has been analyzed. The presence of the defect resulted in the appearance of a pass band, associated with the defect eigenmode, inside the lattice band gap and it was demonstrated that the position of the pass band depended strongly on the parameters of the defect as well as the field structure. The experimental and theoretical results obtained are compared and discussed.
91(2007); http://dx.doi.org/10.1063/1.2801706View Description Hide Description
The lasing properties of an optimized two-dimensional photonic crystalstructure with an organic gain material are investigated. The feedback structure which is fabricated in a thin film of increases both the index contrast from the gain material as well as the optical confinement. By combining first-order and second-order photonic crystalstructures, losses occuring at the edge of the second order structure are dramatically reduced leading to a lower laser threshold and/or to a much smaller footprint of the laser.
91(2007); http://dx.doi.org/10.1063/1.2793175View Description Hide Description
In this letter, the transmission efficiency around waveguide bend on the surface of photonic crystal is investigated. Light is confined to the photonic crystal-air interface by means of surface modes. The transmission efficiency around surface waveguide bend is shown to be very poor. This is due to the phase mismatch of the wave vectors between different sections of the surface waveguide bend. To reduce the phase mismatch between the different waveguide sections, the cell properties at the bend section are modified. As a result, high transmission efficiency of more than 93% around the modified surface waveguide bend structure is achieved.
Temperature dependence of polarized electroluminescence from nonpolar -plane InGaN-based light emitting diodes91(2007); http://dx.doi.org/10.1063/1.2800817View Description Hide Description
An accurate method of estimating polarized light emission was presented for nonpolar -plane InGaN-based blue light emitting diodes, where the unpolarized component caused by unintentional light scattering was eliminated as noise. The polarization ratios of electroluminescence (EL) at 300 and were 0.85 and 0.98, respectively. The energy difference between the highest and the second highest valence bands was estimated to be from the temperature dependence of the spectrally integrated EL intensities under the assumption of Fermi statistics. This value agreed with the one obtained directly from the difference of the EL peak energies between two polarized components, the electric fields perpendicular and parallel to the axis.
91(2007); http://dx.doi.org/10.1063/1.2801983View Description Hide Description
We describe the design and operation of two pneumatically actuated adaptive lenses with refractive power adjustable by diopters. The refractive element in the lenses is a transparent flexible membrane. When vacuum is applied, the membrane is deformed and becomes a diverging meniscus lens. The two lenses have membranes with 18 and diameters and 5 and transition times after sudden changes in pressure. Both lenses can be driven at with 4 diopter variation in the refractive power. The adaptive lenses can be used for longitudinal scanning in three-dimensional imaging and for fast focusing.
91(2007); http://dx.doi.org/10.1063/1.2802043View Description Hide Description
We report on a photon detector aimed at low light detection, which is based on the combination of small sensing volumes and large absorbing regions. Fabricated devices show stable gain values in the range of 1000–10 000 at bias voltages of at at room temperature. Submicron devices show dark current less than and unity gain dark current density values less than . The noise equivalent power (NEP) is measured to be at room temperature without any gating, which is similar to NEP of current avalanche photodetectors in gated operation.
91(2007); http://dx.doi.org/10.1063/1.2802082View Description Hide Description
Stable dual-wavelength operation of InGaAs diode lasers coupled with volume Bragg gratings has been demonstrated for the continuous wave and gain-switching regimes. Spectral narrowing down to has been realized with maximum output power of up to from a broad area stripe laser diode in a single-grating external cavity configuration. Spectral separation from 0.5 has been obtained and an output power of up to was achieved in dual-wavelength operation.
Increase of light extraction from GaN based light emitting diodes incorporating patterned structure by colloidal lithography91(2007); http://dx.doi.org/10.1063/1.2802557View Description Hide Description
The light extraction efficiency of light emitting diodes(LEDs) was enhanced by incorporating nanoscale patterns inside the LED structure. A hole patterned layer and a pillar patterned indium-tin-oxide (ITO) contact layer were fabricated by using colloidallithography with size-tunable polystyrene spheres. It was found that the light output power (at ) of the LEDs with the hole patterned layer and the pillar patterned ITO contact layer were enhanced by 21% and 10%, respectively, compared with the conventional LED due to the increase of the extraction probability of the internally reflected photons through the patterns.
Enhanced photoluminescence from Er-doped AlGaAs wet thermal native oxides by postoxidation implantation91(2007); http://dx.doi.org/10.1063/1.2802560View Description Hide Description
A significant enhancement in the , cw photoluminescence (PL) from Er-doped native oxide films is achieved by incorporating the Er after (relative to before) wet thermal oxidation of the AlGaAs. Postoxidation Er ion implantation ( and ) prevents the formation of nonradiative ErAs complexes, leading to a relatively long fluorescence lifetime (an approximately seven times improvement) with approximately three times enhancement in the PL intensity. The data suggest that Er-doped AlGaAs native oxides formed using postoxidation implantation may be a viable active media for monolithic optoelectronic integration of waveguide amplifiers on GaAs substrates.
91(2007); http://dx.doi.org/10.1063/1.2802576View Description Hide Description
The authors present experimental results of self-referenced spiral interference realized by a hollow spiral phase plate fabricated by electron beam lithography. Comparing with conventional interference systems, the proposed phase element provides a simple and robust approach to obtaining spiral interference fringes in a self-referenced interferometric way. Experimental implementation confirms that the element can be employed as an external tool kit for simple modification of existing optical microscopes to interferometers.
91(2007); http://dx.doi.org/10.1063/1.2803069View Description Hide Description
We demonstrate a high bit-rate optical signal transmission by using long-range surface plasmon polariton (LRSPP) waves in a guided geometry. With a optical communication signal, eye patterns and bit-error-rates were measured to access the quality of the transmission properties of the LRSPP mode. A thin gold strip line embedded in a low loss optical polymer supports a LRSPP mode, which propagates with a loss, and couples to standard single mode fibers at with a coupling loss. A optical signal was transmitted via a long LRSPP waveguide without any distortion of the eye patterns. The experiment also showed error-free transmissions. These results indicate that the LRSPP waveguide is a potential transmission line for optical interconnections overcoming the inherent problems in electric interconnections.
91(2007); http://dx.doi.org/10.1063/1.2804561View Description Hide Description
We report magnetic circular dichroism measurements on thin GaMnAs films with low Mn concentration, which reveal that exchange-induced spin splitting of the band edges occurs only in samples that show ferromagnetic order, and is not observed in paramagnetic samples. These results lead to the conclusion that Mn ions in the configuration provide the only mechanism for exchange interaction between Mn spins and band carriers. We also show that there is a linear relation between the observed exchange-induced splitting of the band edges and the Curie temperature, pointing to a common origin of the band edge splitting and ferromagnetism in GaMnAs.
Lossless all-optical phase gate using a polarization-division Sagnac interferometer applicable to a waveguide-type Kerr medium91(2007); http://dx.doi.org/10.1063/1.2801697View Description Hide Description
We propose an apparatus that realizes direct observation of nonlinear phase shifts induced by cross-phase modulation. The apparatus is based on a polarization-division Sagnac interferometer incorporating Faraday rotators, which, in principle, enables phase robustness, flexibility, and lossless operation. Here, we present the measurement of nonlinear phase shifts in a photonic crystal fiber, demonstrating the advantage of our system in its application to waveguide-type Kerr media. This apparatus is applicable to lossless all-optical phase gates and switches.
Thick film laser induced forward transfer for deposition of thermally and mechanically sensitive materials91(2007); http://dx.doi.org/10.1063/1.2799877View Description Hide Description
Laser forward transfer processes incorporating thin absorbing films can be used to deposit robust organic and inorganic materials but the deposition of more delicate materials has remained elusive due to contamination and stress induced during the transfer process. Here, we present the approach to high resolution patterning of sensitive materials by incorporating a thick filmpolymer absorbing layer that is able to dissipate shock energy through mechanical deformation. Multiple mechanisms for transfer as a function of incident laser energy are observed and we show viable and contamination-free deposition of living mammalian embryonic stem cells.