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1 Feb 2010

Volume 96, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 053107 (2010); http://dx.doi.org/10.1063/1.3280078 (3 pages)

Desalegne Teweldebrhan, Vivek Goyal, Muhammad Rahman, and Alexander A. Balandin
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Wavelength-stable cyan and green light emitting diodes on nonpolar m-plane GaN bulk substrates

Theeradetch Detchprohm, Mingwei Zhu, Yufeng Li, Liang Zhao, Shi You, Christian Wetzel, Edward A. Preble, Tanya Paskova, and Drew Hanser

Appl. Phys. Lett. 96, 051101 (2010); http://dx.doi.org/10.1063/1.3299257 (3 pages) | Cited 9 times

Online Publication Date: 1 February 2010

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We report the development of 480 nm cyan and 520 nm green light emitting diodes (LEDs) with a highly stable emission wavelength. The shift is less than 3 nm when the drive current density is changed from 0.1 to 38 A/cm2. LEDs have been obtained in GaInN-based homoepitaxy on nonpolar m-plane GaN bulk substrates. For increasing emission wavelength we find a large number of additional dislocations generated within the quantum wells (2×108 to ∼ 1010 cm2) and a decrease in the electroluminescence efficiency. This suggests that the strain induced generation of defects plays a significant role in the performance limitations.
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85.60.Jb Light-emitting devices

Enormously high-peak-power optical pulse generation from a single-transverse-mode GaInN blue-violet laser diode

Masaru Kuramoto, Tomoyuki Oki, Tomoya Sugahara, Shunsuke Kono, Masao Ikeda, and Hiroyuki Yokoyama

Appl. Phys. Lett. 96, 051102 (2010); http://dx.doi.org/10.1063/1.3299261 (3 pages) | Cited 9 times

Online Publication Date: 1 February 2010

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We have demonstrated extraordinary optical pulse generation with a peak-power of 55 W and pulse duration of 15 ps by intense electrical pulse excitation of a 401 nm GaInN laser diode (LD). Electrical pulse excitation of a GaInN LD which contained a thicker electron blocking layer gave rise to abnormal behavior with a several nanosecond-long delay and apparent Q-switching under intense excitation. Operation of this LD under such excitation was found to produce highly intense optical pulses even in semiconductor lasers with a single-transverse-mode.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Binary liquid crystal alignments based on photoalignment in azo dye-doped liquid crystals and their application

Andy Ying-Guey Fuh, Ju-Chin Chen, San-Yi Huang, and Ko-Ting Cheng

Appl. Phys. Lett. 96, 051103 (2010); http://dx.doi.org/10.1063/1.3299268 (3 pages) | Cited 9 times

Online Publication Date: 1 February 2010

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This work demonstrates the feasibility of binary liquid crystal (LC) alignments, in which two forms of LC alignment are in a single pixel or a specific area using a surface-treated alignment layer and a photoalignment film of the adsorption of azo dyes onto the polymer surface in azo dye-doped liquid crystals. Binary LC alignments that involve two of common LC alignments, which are homogeneous, homeotropic, hybrid, and twisted nematic alignments, are initially demonstrated. Then, a binary LC alignment that comprises hybrid and homeotropic alignments is adopted to fabricate a viewing-angle-dependent liquid crystal display, which displays two images by changing viewing angles.
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42.79.Kr Display devices, liquid-crystal devices
61.30.-v Liquid crystals
42.70.Df Liquid crystals
68.47.Mn Polymer surfaces

Multimode resonances in metallically confined square-resonator microlasers

Kai-Jun Che, Yue-De Yang, and Yong-Zhen Huang

Appl. Phys. Lett. 96, 051104 (2010); http://dx.doi.org/10.1063/1.3302406 (3 pages) | Cited 6 times

Online Publication Date: 1 February 2010

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Directional emission InP/AlGaInAs square-resonator microlasers with a side length of 20 μm are fabricated by standard photolithography and inductively coupled-plasma etching technique. Multimode resonances with about seven distinct mode peaks in a free-spectral range are observed from 1460 to 1560 nm with the free-spectral range of 12.1 nm near the wavelength of 1510 nm, and the mode refractive index versus the photon energy E (eV) as 3.07152+0.18304E are obtained by fitting the laser spectra with an analytical mode wavelength formula derived by light ray method. In addition, mode field pattern is simulated for cold cavity by two dimensional finite-difference time-domain technique.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
02.70.Bf Finite-difference methods
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.16.Nd Micro- and nanolithography
81.05.Ea III-V semiconductors

Subwavelength plastic wire terahertz time-domain spectroscopy

Borwen You, Ja-Yu Lu, Tze-An Liu, Jin-Long Peng, and Ci-Ling Pan

Appl. Phys. Lett. 96, 051105 (2010); http://dx.doi.org/10.1063/1.3279154 (3 pages) | Cited 3 times

Online Publication Date: 1 February 2010

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This work demonstrates the feasibility of a terahertz time-domain spectrometer based on a subwavelength-diameter plastic wire (SPW) for sensing applications. The dispersion property of the SPW is experimentally and theoretically studied. The SPW exhibits a low and controllable waveguide dispersion, which can be engineered by changing the core diameter, the core index, and the cladding index of the wire. Two white powders, tryptophan and polyethylene, deposited on the bottom of the wire can be successfully distinguished based on the waveguide dispersion of SPW. The SPW would be a promising candidate for combination with biochips for sensing minute molecules.
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87.64.K- Spectroscopy
87.15.M- Spectra of biomolecules
84.40.Az Waveguides, transmission lines, striplines

Optical gain improvement in type-II InGaN/GaNSb/GaN quantum well structures composed of InGaN/and GaNSb layers

Seoung-Hwan Park, Doyeol Ahn, Bun-Hei Koo, and Jae-Eung Oh

Appl. Phys. Lett. 96, 051106 (2010); http://dx.doi.org/10.1063/1.3300840 (3 pages) | Cited 8 times

Online Publication Date: 2 February 2010

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Optical gain characteristics of type-II InGaN/GaNSb quantum well (QW) structure are investigated by using the multiband effective mass theory. These results are compared with those of conventional InGaN/GaN QW structures. The transition wavelength rapidly increases with increasing the Sb composition in GaNSb layer while it is less sensitive to the In composition in InGaN layer. Hence, longer wavelength QW structures with a relatively lower In composition can be easily obtained by controlling Sb composition, compared to the conventional type-I InGaN/GaN QW structures. The optical gain and the differential gain (dg/dn) of a type-II QW structure are shown to be much larger than that of a conventional QW structure in an investigated range of carrier densities. This is due to the reduction in the effective well width, in addition to the increase in the optical matrix element.
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78.67.De Quantum wells
78.66.Fd III-V semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

The impact of piezoelectric polarization and nonradiative recombination on the performance of (0001) face GaN/InGaN photovoltaic devices

J. J. Wierer, A. J. Fischer, and D. D. Koleske

Appl. Phys. Lett. 96, 051107 (2010); http://dx.doi.org/10.1063/1.3301262 (3 pages) | Cited 17 times

Online Publication Date: 2 February 2010

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The impact of piezoelectric polarization and nonradiative recombination on the short-circuit current densities (Jsc) of (0001) face GaN/InGaN photovoltaic devices is demonstrated. P-i-n diodes consisting of 170 nm thick intrinsic In0.09Ga0.91N layers sandwiched by GaN layers exhibit low Jsc ∼ 40 μA/cm2. The piezoelectric polarization at the GaN/InGaN heterointerfaces creates drift currents opposite in direction needed for efficient carrier collection. Also, nonradiative recombination centers produce short carrier lifetimes, limiting Jsc. Alternative structures with intrinsic InGaN layers sandwiched by n-type InGaN or graded InyGa1−yN (y = 0–0.09) layer and a p-type In0.015Ga0.985N layer have favorable potentials, longer carrier lifetimes, and improve Jsc to ∼ 0.40 mA/cm2.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.22.Ej Polarization and depolarization
77.55.H- Piezoelectric and electrostrictive films
81.05.Ea III-V semiconductors

Hollow-core resonator based on out-of-plane two-dimensional photonic band-gap crystal cladding at microwave frequencies

Georges Humbert, Jean-Michel Le Floch, David Mouneyrac, Denis Férachou, Michel Aubourg, Michael E. Tobar, Dominique Cros, and Jean-Marc Blondy

Appl. Phys. Lett. 96, 051108 (2010); http://dx.doi.org/10.1063/1.3303857 (3 pages) | Cited 2 times

Online Publication Date: 2 February 2010

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We report on the demonstration of a resonator based on electromagnetic field confinement in a hollow-core by implementing an out-of-plane two-dimensional (2D) photonic band-gap (PBG) crystal cladding. In contrast with in-plane 2D PBG crystal devices, the PBG crystal studied here is perpendicular to the propagation axis. A resonator was constructed with silica rods to prove the concept at frequencies around 30 GHz. We show that the technique has the potential to reach quality factors (Q) of 5×105.
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42.79.-e Optical elements, devices, and systems
42.81.Bm Fabrication, cladding, and splicing
42.70.Qs Photonic bandgap materials

Improved crystal quality and performance of GaN-based light-emitting diodes by decreasing the slanted angle of patterned sapphire

Ji-Hao Cheng, YewChung Sermon Wu, Wei-Chih Liao, and Bo-Wen Lin

Appl. Phys. Lett. 96, 051109 (2010); http://dx.doi.org/10.1063/1.3304004 (3 pages) | Cited 14 times

Online Publication Date: 2 February 2010

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Periodic triangle pyramidal array patterned sapphire substrates (PSSs) with various slanted angles were fabricated by wet etching. It was found beside normal wurtzite GaN, zinc blende GaN was found on the sidewall surfaces of PSS. The crystal quality and performance of PSS-LEDs improved with decrease in slanted angle from 57.4° to 31.6°. This is because most of the growth of GaN was initiated from c-planes. As the growth time increased, GaN epilayers on the bottom c-plane covered these pyramids by lateral growth causing the threading dislocation to bend toward the pyramids.
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85.60.Jb Light-emitting devices
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Lk Linear defects: dislocations, disclinations

Second-harmonic generation from a single wurtzite GaAs nanoneedle

Roger Chen, Shanna Crankshaw, Thai Tran, Linus C. Chuang, Michael Moewe, and Connie Chang-Hasnain

Appl. Phys. Lett. 96, 051110 (2010); http://dx.doi.org/10.1063/1.3304118 (3 pages) | Cited 6 times

Online Publication Date: 2 February 2010

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We report and characterize second-harmonic generation from a single wurtzite GaAs nanoneedle. The wurtzite crystal structure of the nanoneedle relaxes the strict nonlinear selection rules of normal zincblende GaAs while maintaining its strong nonlinear optical coefficients. The ability to grow GaAs nanoneedles without catalysts on (111) Si makes them particularly attractive as nonlinear optoelectronic media compatible with complementary metal-oxide-semiconductor technology.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.46.-w Structure of nanoscale materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Ultrafast saturable absorption devices incorporating efficiently electrosprayed carbon nanotubes

Suho Chu, Won-Suk Han, Il-Doo Kim, Young-Geun Han, Kwanil Lee, Sang Bae Lee, and Yong-Won Song

Appl. Phys. Lett. 96, 051111 (2010); http://dx.doi.org/10.1063/1.3295699 (3 pages) | Cited 4 times

Online Publication Date: 3 February 2010

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We demonstrate saturable absorption operation of single-walled carbon nanotubes (CNTs) deposited by an efficient electrospray process that provides target-localized deposition with a homogeneous dispersion of the nanomaterials. An improvement in deposition efficiency of 95% is achieved. CNT dispersion/deposition conditions are optimized for suppressed CNT agglomeration, thereby maximizing the nonlinear absorption of CNTs. An ultrafast saturable absorber is formed with side-polished fiber as a substrate for evanescent field interaction of propagated light with CNTs. A resultant fiber mode-locked laser is realized. The laser has output with an estimated pulse duration and repetition rate of 190.9 fs and 3.95 MHz, respectively.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Room temperature operation of photonic-crystal distributed-feedback quantum cascade lasers with single longitudinal and lateral mode performance

Quan-Yong Lu, Wan-Hong Guo, Wei Zhang, Li-Jun Wang, Jun-Qi Liu, Lu Li, Feng-Qi Liu, and Zhan-Guo Wang

Appl. Phys. Lett. 96, 051112 (2010); http://dx.doi.org/10.1063/1.3295704 (3 pages) | Cited 9 times

Online Publication Date: 3 February 2010

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We demonstrate room temperature operation of photonic-crystal distributed-feedback quantum cascade lasers emitting at 4.7 μm. A rectangular photonic crystal lattice perpendicular to the cleaved facet was defined using holographic lithography. The anticrossing of the index- and Bragg-guided dispersions of rectangular lattice forms the band-edge mode with extended mode volume and reduced group velocity. Utilizing this coupling mechanism, single mode operation with a near-diffractive-limited divergence angle of 12° is obtained for 33 μm wide devices in a temperature range of 85–300 K. The reduced threshold current densities and improved heat dissipation management contribute to the realization of devices’ room temperature operation.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.40.-i Holography

Effect of Mg doping in the barrier of InGaN/GaN multiple quantum well on optical power of light-emitting diodes

Sang-Heon Han, Chu-Young Cho, Sang-Jun Lee, Tae-Young Park, Tae-Hun Kim, Seung Hyun Park, Sang Won Kang, Je Won Kim, Yong Chun Kim, and Seong-Ju Park

Appl. Phys. Lett. 96, 051113 (2010); http://dx.doi.org/10.1063/1.3302458 (3 pages) | Cited 8 times

Online Publication Date: 3 February 2010

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We report on Mg doping in the barrier layers of InGaN/GaN multiple quantum wells (MQWs) and its effect on the properties of light-emitting diodes (LEDs). Mg doping in the barriers of MQWs enhances photoluminescence intensity, thermal stability, and internal quantum efficiency of LEDs. The light output power of LEDs with Mg-doped MQW barriers is higher by 19% and 27% at 20 and 200 mA, respectively, than that of LEDs with undoped MQW barriers. The improvement in output power is attributed to the enhanced hole injection to well layers in MQWs with Mg-doped barriers.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors

A microtip self-written on a vertical-cavity surface-emitting laser by photopolymerization

V. Bardinal, B. Reig, T. Camps, E. Daran, J. B. Doucet, C. Turck, J. P. Malval, D. J. Lougnot, and O. Soppera

Appl. Phys. Lett. 96, 051114 (2010); http://dx.doi.org/10.1063/1.3303980 (3 pages) | Cited 5 times

Online Publication Date: 3 February 2010

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We present the integration of a self-aligned microtip on a vertical-cavity surface-emitting laser (VCSEL) by near infrared photopolymerization. This one-step fabrication process is triggered by the laser source itself. It is based on the use of photopolymers sensitive at the lasing wavelength and can be applied to VCSEL devices after their process fabrication. We have characterized the fabricated microtips and shown that they focus laser light at few micrometers from the device. The applications of this simple method may concern VCSEL beam shaping as well as the fabrication of microprobes for near-field optical microscopy.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
82.35.-x Polymers: properties; reactions; polymerization
42.70.Jk Polymers and organics

How many surface plasmons are locally excited on the ridges of metallic lamellar gratings?

B. Wang and P. Lalanne

Appl. Phys. Lett. 96, 051115 (2010); http://dx.doi.org/10.1063/1.3304021 (3 pages) | Cited 10 times

Online Publication Date: 3 February 2010

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In contrast to earlier classical studies that analyze the surface Bloch modes supported by metallic gratings composed of slits as collective surface-plasmon-polaritons (SPPs) resonances (or poles) of the entire periodic problem, we study the normalized rate of SPPs that are locally launched on every individual ridge of metallic lamellar gratings. With this “microscopic” description at the unit-cell level, we further explain how these individual SPPs constructively interfere to build up the classical collective resonances. The approach, which combines analytical treatments and fully-vectorial computations, shines new light on an important and classical phenomenon of grating diffraction.
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42.79.Dj Gratings

Microscopic simulation of nonequilibrium features in quantum-well pumped semiconductor disk lasers

Eckhard Kühn, Stephan W. Koch, Angela Thränhardt, Jörg Hader, and Jerome V. Moloney

Appl. Phys. Lett. 96, 051116 (2010); http://dx.doi.org/10.1063/1.3294628 (3 pages) | Cited 1 time

Online Publication Date: 3 February 2010

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A microscopically motivated nonequilibrium theory is applied to study the power characteristics of an in-well pumped vertical external cavity surface emitting Laser for varying pump energies. Dynamic simulations yield steady state nonequilibrium carrier distributions resulting in gain reduction due to kinetic hole burning. Pauli blocking effects become prominent for more resonant pumping and increased pump powers. The reduced pump absorption results in a sublinear input-output power characteristics even for the optimized case where heating of the active mirror plays no role.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.79.Bh Lenses, prisms and mirrors
42.60.By Design of specific laser systems

Quantitative phase imaging with broadband fields

Zhuo Wang and Gabriel Popescu

Appl. Phys. Lett. 96, 051117 (2010); http://dx.doi.org/10.1063/1.3304787 (3 pages) | Cited 13 times

Online Publication Date: 3 February 2010

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Recently, Wolf has shown that the phase measurement associated with fields that are not monochromatic, which is relevant for all x-ray structure investigations, must be properly defined via a cross-spectral density function under full spatial coherence conditions; otherwise, the problem is meaningless and has no solution [ E. Wolf, Phys. Rev. Lett. 103, 075501 (2009) ]. We propose an experimental realization for retrieving the phase across the entire field of an image. The demonstration is performed using broadband optical fields, but can be extended to other electromagnetic radiation, including x-rays.
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61.05.cf X-ray scattering (including small-angle scattering)

rf linewidth reduction in a quantum dot passively mode-locked laser subject to external optical feedback

C.-Y. Lin, F. Grillot, N. A. Naderi, Y. Li, and L. F. Lester

Appl. Phys. Lett. 96, 051118 (2010); http://dx.doi.org/10.1063/1.3299714 (3 pages) | Cited 11 times

Online Publication Date: 4 February 2010

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The effect of external optical feedback on an InAs/GaAs quantum dot passively mode-locked laser is investigated. The rf linewidth narrows from 8 KHz in the free-running situation to a value as low as 350 Hz under relatively low feedback. The rf linewidth characterization under resonant feedback at a multiple of the laser cavity length validates the prediction of a previous numerical simulation. It is also confirmed that the integrated rms timing jitter varies as the square root of the rf linewidth. The results are promising for the development of compact, monolithic semiconductor mode-locked lasers as low noise optoelectronic oscillators.
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42.55.Px Semiconductor lasers; laser diodes
05.45.Xt Synchronization; coupled oscillators

Surface plasmon excitation in silver nanowires directly deposited on a laser diode chip

Zhe Ma, Xining Zhang, Xin Guo, Qing Yang, Yaoguang Ma, and Limin Tong

Appl. Phys. Lett. 96, 051119 (2010); http://dx.doi.org/10.1063/1.3294626 (3 pages) | Cited 6 times

Online Publication Date: 4 February 2010

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We demonstrate surface plasmon (SP) excitation in silver nanowires directly deposited on the emission facet of a laser diode (LD) chip. Evident light output from the silver nanowires is observed. The output is linear-polarized and is strongly dependent on the nanowire orientation. SP excitation at the central part of a silver nanowire is also observed. The possibility of direct SP excitation on an LD chip may open opportunities for realizing plasmonic and photonic circuits or components with high compactness.
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73.22.Lp Collective excitations
42.55.Px Semiconductor lasers; laser diodes
81.07.Gf Nanowires
78.66.Bz Metals and metallic alloys

Dual wavelength emission from a terahertz quantum cascade laser

Joshua R. Freeman, Julien Madéo, Anthony Brewer, Sukhdeep Dhillon, Owen P. Marshall, Nathan Jukam, Dimitri Oustinov, Jerome Tignon, Harvey E. Beere, and David A. Ritchie

Appl. Phys. Lett. 96, 051120 (2010); http://dx.doi.org/10.1063/1.3304783 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2010

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We describe a heterogeneous terahertz (THz) quantum cascade laser that is composed of two different active region designs. This device emits simultaneously at around 2.5 and 2.9 THz with certain frequency tunability by applied current. We also investigate the spectral gain in the structure by THz time-domain spectroscopy and correlate the gain spectral bandwidth with the alignment and wavelength emission behavior of the two stack device.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Space charge limited electron emission from a Cu surface under ultrashort pulsed laser irradiation

W. Wendelen, D. Autrique, and A. Bogaerts

Appl. Phys. Lett. 96, 051121 (2010); http://dx.doi.org/10.1063/1.3292581 (3 pages) | Cited 4 times

Online Publication Date: 5 February 2010

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In this theoretical study, the electron emission from a copper surface under ultrashort pulsed laser irradiation is investigated using a one-dimensional particle in cell model. Thermionic emission as well as multiphoton photoelectron emission were taken into account. The emitted electrons create a negative space charge above the target; consequently the generated electric field reduces the electron emission by several orders of magnitude. The simulations indicate that the space charge effect should be considered when investigating electron emission related phenomena in materials under ultrashort pulsed laser irradiation of metals.
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79.40.+z Thermionic emission
79.20.Ds Laser-beam impact phenomena
77.22.Jp Dielectric breakdown and space-charge effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Graphene mode-lockers for fiber lasers functioned with evanescent field interaction

Yong-Won Song, Sung-Yeon Jang, Won-Suk Han, and Mi-Kyung Bae

Appl. Phys. Lett. 96, 051122 (2010); http://dx.doi.org/10.1063/1.3309669 (3 pages) | Cited 46 times

Online Publication Date: 5 February 2010

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Employing graphene as an intracavity passive power modulating element, we demonstrate the efficient laser pulsation in high pulse-energy regime with evanescent field interaction between the propagating light and graphene layer. Graphene is prepared by the solution based reduction of graphene oxide, and dispersed homogeneously into the water for spray onto an all-fiber substrate, side-polished fiber. With the intracavity power up to 21.41 dBm, we ensure the robust high-energy operation without any thermal damage of graphene. Resultant output pulses have center wavelength, spectral width, and repetition rate of 1561.6 nm, 1.96 nm, and 6.99 MHz, respectively.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Demonstration of an air-slot mode-gap confined photonic crystal slab nanocavity with ultrasmall mode volumes

Jie Gao, James F. McMillan, Ming-Chung Wu, Jiangjun Zheng, Solomon Assefa, and Chee Wei Wong

Appl. Phys. Lett. 96, 051123 (2010); http://dx.doi.org/10.1063/1.3298642 (3 pages) | Cited 15 times

Online Publication Date: 5 February 2010

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We demonstrate experimentally an air-slot mode-gap photonic crystal cavity with quality factor of 104 and modal volume of 0.02 cubic wavelengths, based on the design of an air-slot in a width-modulated line-defect in a photonic crystal slab. The origin of the high Q air-slot cavity mode is the mode-gap effect from the slotted PhCWG mode with negative dispersion. The high Q cavities with ultrasmall mode volume are important for applications such as cavity quantum electrodynamics, nonlinear optics, and optical sensing.
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42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Enhanced optical power and low forward voltage of GaN-based light-emitting diodes with Ga-doped ZnO transparent conducting layer

Tae-Young Park, Yong-Seok Choi, Jang-Won Kang, Jae-Ho Jeong, Seong-Ju Park, Dong Min Jeon, Je Won Kim, and Yong Chun Kim

Appl. Phys. Lett. 96, 051124 (2010); http://dx.doi.org/10.1063/1.3298644 (3 pages) | Cited 17 times

Online Publication Date: 5 February 2010

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Ga-doped ZnO (ZnO:Ga) films were grown by metalorganic chemical vapor deposition as transparent conducting layers for GaN light-emitting diodes (LEDs). The forward voltage of LEDs with ZnO:Ga was 3.3 V at 20 mA. The low forward voltage was attributed to the removal of a resistive ZnGa2O4 phase, decreased resistivity of ZnO:Ga films, and increased hole concentration in p-GaN by thermal annealing process. The light output power of LEDs with ZnO:Ga was increased by 25% at 20 mA compared to that of LEDs with Sn-doped indium oxide due to the enhanced transmittance and the increased hole concentration in p-GaN.
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85.60.Jb Light-emitting devices
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Ea III-V semiconductors

Gyrotropic photonic crystal waveguide switches

Z. Wu, Miguel Levy, V. J. Fratello, and A. M. Merzlikin

Appl. Phys. Lett. 96, 051125 (2010); http://dx.doi.org/10.1063/1.3309715 (3 pages) | Cited 3 times

Online Publication Date: 5 February 2010

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Functional photonic crystals fabricated in iron garnet films are shown to provide magnetically-controllable optical switching. Transverse-electric and transverse-magnetic stop band separation in conjunction with optical gyrotropy are utilized to selectively block and transmit near-infrared light in waveguide geometries. Geometrical birefringence allows the simultaneous low- and high-birefringence in different modes necessary to create band gap separation and effective magneto-optic gyrotropy in a single device.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Gn Optical waveguides and couplers
85.70.Sq Magnetooptical devices
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