Volume 94, Issue 23, 08 June 2009
- 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
- organic electronics and photonics
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
We present a route to functionalize chemically and magnetically silicon surfaces by a local passivation, taking advantage of Stranski–Krastanov growth mode of the Au–Si(111) system. Metal-rich Au-silicide nanoparticles, supported on a Si-rich two-dimensional Au-silicide layer, are obtained. Subsequently deposited Co is used to form magnetic nanostructures. The two Au silicides display a different chemical reactivity with Co enabling the fabrication of localized magnetic Co nanodots. These magnetic nanostructures can be aligned along step bunches of a vicinal Si(111) surface. By varying the growth parameters, the particle density can be tuned from to the low .
- LASERS, OPTICS, AND OPTOELECTRONICS
94(2009); http://dx.doi.org/10.1063/1.3141480View Description Hide Description
We present multiphotonimaging based on semiconductor planar waveguide technology which can be used as a transmitter and receiver simultaneously. In particular, silicon on insulator waveguides with diode structures are used to demonstrate resolution three-photon imaging of microparticles by using 1550 nm excitation. Additional theoretical study has been performed to demonstrate the proposed scheme for three-dimensional tomography of micron-sized objects, which could be realized by using multiple transmitter-detector pairs.
94(2009); http://dx.doi.org/10.1063/1.3144270View Description Hide Description
A lateral photovoltaic effect was observed in -plane GaN films grown on -plane sapphire at room temperature. Under various light sources illuminations, contacts along the -axis exhibited about ten times the photovoltage than those along the -axis, which kept linear relationship with the illumination intensity. It was attributed to anisotropic in-plane electrical field induced by the intrinsic spontaneous/piezoelectric polarization, which spatially separated photogenerated carriers to produce the photovoltage.
94(2009); http://dx.doi.org/10.1063/1.3151866View Description Hide Description
ZnO nanostructures attract current interest because they have the potential to implement cavity quantum electrodynamics at room temperature. We report a photoluminescence mapping of ZnOnanobelts both at room temperature and 4.2 K. The multicavity modes were observed all over the belt surface, which were induced by Fabry–Pérot interference. The emission from the belt surface is enhanced at both the ends and the sides of the belt, and is highly linearly polarized in the direction perpendicular to the long axis of the belt. The results are explained using finite-difference time-domain simulations.
94(2009); http://dx.doi.org/10.1063/1.3151920View Description Hide Description
We present a method for measuring the orbital angular momentum (OAM) of optical vortices through extracting the phase values sampled by a multipinhole plate. We demonstrate that the phase of an optical vortex passing through a multipinhole plate can be directly extracted from the Fourier transform of a single diffraction intensity pattern according to a simple algorithm and thus the state or the OAM of the photons can be measured quantitatively.
Dislocation density reduction in GaN by dislocation filtering through a self-assembled monolayer of silica microspheres94(2009); http://dx.doi.org/10.1063/1.3152012View Description Hide Description
We demonstrate the use of self-assembledmonolayers of silica microspheres as selective growth masks for significant threading dislocation density reduction in GaN on sapphire epilayers. During GaN regrowth through the close-packed monolayer, the silica microspheres effectively terminate the propagation of threading dislocations. As a result, the threading dislocation density, measured by large area atomic force microscopy and cathodoluminescence scans, is reduced from to . This nearly two orders of magnitude reduction is attributed to dislocation blocking and bending by the unique interface between GaN and silica microspheres.
Coherent beam combination of two-dimensional high power fiber amplifier array using stochastic parallel gradient descent algorithm94(2009); http://dx.doi.org/10.1063/1.3152282View Description Hide Description
We demonstrate coherent beam combination of two-dimensional high power fiber amplifier array using stochastic parallel gradient descent (SPGD) algorithm. Four polarization-maintained fiber amplifiers are tiled side by side into a laser array with a fill factor of 54% in the near-field. Phase control on the fiber amplifiers are performed by running SPGD algorithm on a digital dignal processor with updating rate of 50 000 Hz/channel. Coherent beam combination of the four fiber amplifiers with a total output power of 60.1 W using SPGD algorithm is demonstrated. Beam quality of the combined beam is computed to be .
94(2009); http://dx.doi.org/10.1063/1.3152290View Description Hide Description
Ablation of LiF crystal by soft x-ray laser (XRL) pulses with wavelength and duration is studied experimentally and theoretically. It is found that a crater appears on a surface of LiF for XRL fluence, exceeding the ablation threshold in one shot, or in each of the three XRL shots. This is substantially below the ablation thresholds obtained with other lasers having longer pulse duration and/or longer wavelength. A mechanism of thermomechanicalablation in large bandgap dielectrics is proposed. The theory explains the low via small attenuation depth, absence of light reflection, and electron heat conductivity.
Excitation and focusing of terahertz surface plasmons using a grating coupler with elliptically curved grooves94(2009); http://dx.doi.org/10.1063/1.3153125View Description Hide Description
Using a diffraction grating with elliptically curved grooves engraved at the top of an aluminum slab, surface plasmons in the terahertz frequency range are efficiently excited with an incoming parallel beam and focused over the metal surface down to the diffraction limit. At 0.5 THz, the lateral confinement of the surface plasmon is 1 mm while its extension in air is 0.74 mm, much smaller than the calculated value for a semi-infinite substrate having the conductivity of bulk aluminum.
94(2009); http://dx.doi.org/10.1063/1.3141485View Description Hide Description
We describe finite-difference time-domain simulations of a two-dimensional photonic crystal implementation of a two-resonator system capable of capturing light pulses from a waveguide. As much as 99.61% of incident pulse energy is captured in simulations. The release of near-perfect Gaussian pulses is also demonstrated.
94(2009); http://dx.doi.org/10.1063/1.3148673View Description Hide Description
We report linewidth properties of active-passive coupled monolithic InGaAssemiconductorring lasers with various length of passive waveguide. It is experimentally confirmed that the linewidth of the lasers is proportional to the square of the ratio of the length of active part of the cavity over the total length of the cavity. The lasers are applicable for communication and sensing devices, which need the narrow linewidth.
Understanding the dispersion of coaxial plasmonic structures through a connection with the planar metal-insulator-metal geometry94(2009); http://dx.doi.org/10.1063/1.3148692View Description Hide Description
We elucidate the dispersion behavior of deep-subwavelength propagating modes in coaxial plasmonicstructures by making an explicit connection with the planar metal-insulator-metal geometry. We provide an intuitive picture that allows for a qualitative understanding and a quantitative prediction of the entiredispersion behavior, which includes the number of modes at every frequency, the modal propagation constants, the propagation losses, and the cutoff frequencies of propagating modes supported by these technologically important structures. We validate our analytical approach by comparing its predictions to first-principles finite-difference frequency-domain simulations.
94(2009); http://dx.doi.org/10.1063/1.3151834View Description Hide Description
We demonstrate that in graphitic nanocarbon materials, combination of ballistic conductivity and strong electron photon coupling opens a unique opportunity to observe transfer of momentum of the electromagnetic radiation to free carriers. The resulting drag of quasiballistically propagating electrons can be employed, in particular, to visualize the temporal profile, polarization, and propagation direction of the laser pulse. In this letter, we report the giant photon drag effect in yarns made of multiwall carbon nanotubes.
94(2009); http://dx.doi.org/10.1063/1.3151864View Description Hide Description
We report a 1.036 GHz gated Geiger mode InGaAsavalanche photodiode with a detection dead time of just 1.93 ns. This is demonstrated by full recovery of the detection efficiency two gate cycles after a detection event, as well as a measured maximum detection rate of 497 MHz. As an application, we measure the second order correlation function of the emission from a diode laser with a single detector that works reliably at high speed owing to the extremely short dead time of the detector. The device is ideal for high bit rate fiber wavelength quantum key distribution and photonic quantum computing.
94(2009); http://dx.doi.org/10.1063/1.3152998View Description Hide Description
We present a principle for the temperature stabilization of photonic crystal(PhC)cavities based on optofluidics. We introduce an analytic method enabling a specific mode of a cavity to be made wavelength insensitive to changes in ambient temperature. Using this analysis, we experimentally demonstrate a PhCcavity with a quality factor of that exhibits a temperature-independent resonance. Temperature-stablecavities constitute a major building block in the development of a large suite of applications from high-sensitivity sensor systems for chemical and biomedical applications to microlasers, optical filters, and switches.
Electromagnetically induced transparency-like effect in a single polydimethylsiloxane-coated silica microtoroid94(2009); http://dx.doi.org/10.1063/1.3149697View Description Hide Description
We study both experimentally and theoretically the coupling between a fiber taper and two whispering-gallery modes, which are simultaneously excited in a single pilydimethyl-siloxane-coated silica microtoroid system. The transmission spectrum of the fiber-coupled two-mode microresonator shows a sharp electromagnetically induced transparency-like window within the resonant absorption region. This line shape results from destructive interference between two optical pathways associated with two distinct coexisting modes in a single resonator. The sharp transparency peak has great potential applications in light modulation and highly sensitive biochemical sensors.
Phase tunable holographic fabrication for three-dimensional photonic crystal templates by using a single optical element94(2009); http://dx.doi.org/10.1063/1.3149705View Description Hide Description
This paper demonstrates a phase tunable holographicfabrication of three-dimensional photoniclattice structures using a single optical element. A top-cut four-side prism is employed to generate five-beam three-dimensional interference patterns. A silica glass slide is inserted into the optical path to adjust the phase of one interfering beam relative to other four beams. The phase control of the interfering laser beam renders the lattice of the interference pattern from a face-center tetragonal symmetry into a high contrast, interconnecting diamondlike symmetry. This method provides a flexible approach to fabricating three-dimensional photonic lattices with improved photonic band structures.
94(2009); http://dx.doi.org/10.1063/1.3152769View Description Hide Description
Photonic crystal(PC) devices require high fabrication accuracy for on demand positioning of resonances. We describe post-fabrication fine-tuning of a PCquantum well infrared photodetector(QWIP) by sidewall-deposition of silicon nitride. The PC resonance was shifted over a bandwidth of . From photoresponse measurements we calculated a tuning coefficient of . The QWIP responsivity did not suffer from nitride absorption while the PC resonance increased by a factor of 1.6. This shows that post-fabrication tuning by dielectric deposition with, e.g., silicon nitride is a feasible method to achieve precise implementations of PC devices.
94(2009); http://dx.doi.org/10.1063/1.3152773View Description Hide Description
Polarity-controlled ZnOthin filmsgrown on different buffer layers were investigated as nonlinear optical materials for second harmonic generation. The effective nonlinear optical coefficient of ZnOgrown on Cr-compound buffer layers showed a higher value than that of ZnOgrown on MgO buffer layers. The correlations among the grain size and surface roughness with the values of were found to be strong. The of the ZnOfilm increased with decrease in the grain size and surface roughness. This relationship could be explained by the increase in reaction interface and the decrease in scattering probability at the surface as decrease in grain size and surface roughness, respectively.
94(2009); http://dx.doi.org/10.1063/1.3152791View Description Hide Description
Polydimethylsiloxane(PDMS) optical microspheres are fabricated and whispering gallery modes with quality factors of in the 1480 nm band are demonstrated. The dependence of the resonance shifts on the input power is investigated in both the transient (blueshift) and the steady-state (redshift) regimes. Moreover, we demonstrate that such high-PDMSoptical resonators can be used as highly sensitive thermal sensors with temperature sensitivity of , which is one order of magnitude higher than conventional silica microsphere resonators. The estimated thermal resolution of the sensor is .
94(2009); http://dx.doi.org/10.1063/1.3148801View Description Hide Description
We have experimentally verified the lasing of a quasiscarred resonance mode (QSRM) in a spiral-shaped InGaAsPmicrocavity laser by pumping the cavity boundary with current injection. To confirm the lasing of a QSRM, a far field pattern is obtained and six laser emission directions are found; one corresponds to the whispering gallery type modes and the other to a QSRM. By observing the spectrum and lasing thresholds, the lasing characteristics of the QSRM are analyzed.