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28 May 2012

Volume 100, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 222402 (2012); http://dx.doi.org/10.1063/1.3700809 (4 pages)

Felix Balhorn, Simon Jeni, Wolfgang Hansen, Detlef Heitmann, and Stefan Mendach
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Metamaterial near-field sensor for deep-subwavelength thickness measurements and sensitive refractometry in the terahertz frequency range

Benjamin Reinhard, Klemens M. Schmitt, Viktoria Wollrab, Jens Neu, René Beigang, and Marco Rahm

Appl. Phys. Lett. 100, 221101 (2012); http://dx.doi.org/10.1063/1.4722801 (4 pages) | Cited 3 times

Online Publication Date: 29 May 2012

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We present a metamaterial-based terahertz (THz) sensor for thickness measurements of subwavelength-thin materials and refractometry of liquids and liquid mixtures. The sensor operates in reflection geometry and exploits the frequency shift of a sharp Fano resonance minimum in the presence of dielectric materials. We obtained a minimum thickness resolution of 12.5 nm (1/16 000 times the wavelength of the THz radiation) and a refractive index sensitivity of 0.43 THz per refractive index unit. We support the experimental results by an analytical model that describes the dependence of the resonance frequency on the sample material thickness and the refractive index.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.60.Hv Refractometers and reflectometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Near infrared two-photon self-confinement in photopolymers for light induced self-written waveguides fabrication

Alberto Barsella, Honorat Dorkenoo, and Loïc Mager

Appl. Phys. Lett. 100, 221102 (2012); http://dx.doi.org/10.1063/1.4722925 (3 pages) | Cited 1 time

Online Publication Date: 29 May 2012

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We present the fabrication of single mode light induced self-written waveguides using two-photon absorption in photopolymers. The measurements are compared to the finite element method simulation of the propagation and demonstrate that two-photon process leads to the confinement of light.
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42.70.Jk Polymers and organics
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers

Cherenkov high-order harmonic generation by multistep cascading in χ(2) nonlinear photonic crystal

Ning An, Huaijin Ren, Yuanlin Zheng, Xuewei Deng, and Xianfeng Chen

Appl. Phys. Lett. 100, 221103 (2012); http://dx.doi.org/10.1063/1.4722931 (4 pages) | Cited 2 times

Online Publication Date: 29 May 2012

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We propose a scheme for efficient Cherenkov high-order harmonic generation. Second to fifth order harmonic wave are observed in a single periodically poled ferroelectric crystal in our experiment. The noncollinear high-order harmonic generation is produced via enhanced Cherenkov second harmonic cascaded with successive multistep sum-frequency generation with simultaneously longitudinal phase-matching. The emission angle and power dependencies are analyzed in detail experimentally, which coincide with theoretical predictions.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
41.60.Bq Cherenkov radiation

Transistor laser optical and electrical linearity enhancement with collector current feedback

H. W. Then, F. Tan, M. Feng, and N. Holonyak, Jr.

Appl. Phys. Lett. 100, 221104 (2012); http://dx.doi.org/10.1063/1.4723874 (3 pages)

Online Publication Date: 29 May 2012

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The three-port quantum well (QW) transistor laser (TL) is shown to provide a unique solution for generating ultra-linear electro-optical signals. With a simple collector current feedback loop, the 3rd order intermodulation distortion in the electrical and optical output signals of the transistor laser can be suppressed by as much 18.2 dB and 8.4 dB, respectively. These results show that the TL can be used for direct electro-optical feedback linearization, because of the base QW carrier-photon interaction, without incurring signal losses at multiple stages of auxiliary external electro-optical conversion circuitry.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.20.Jq Electro-optical effects

Temperature dependent distinct coupling and dispersions of heavy- and light-hole excitonic polaritons in ZnO

C. C. Zheng, S. J. Xu, J. Q. Ning, Y. N. Chen, F. Zhang, and C. M. Che

Appl. Phys. Lett. 100, 221105 (2012); http://dx.doi.org/10.1063/1.4722933 (4 pages) | Cited 3 times

Online Publication Date: 30 May 2012

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Distinct coupling behavior of heavy- and light-hole excitonic polaritons in ZnO was unveiled by investigating the optical reflectance spectra of a high quality ZnO single crystal as a function of temperature both experimentally and theoretically. A resonance like coupling region was found at a temperature of around 50 K at which several relevant physical quantities such as the transverse exciton transition energy, polarizability, and damping parameters of the two kinds of excitonic polaritons were revealed to overturn. Calculated dispersions correctly reflect the nature of coupled photon and exciton and reproduce the spectral structures of the interacting polaritons.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Fy Semiconductors
71.35.-y Excitons and related phenomena
71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds

Spatio-temporal mapping of ablated species in ultrafast laser-produced graphite plasmas

K. F. Al-Shboul, S. S. Harilal, and A. Hassanein

Appl. Phys. Lett. 100, 221106 (2012); http://dx.doi.org/10.1063/1.4722939 (4 pages) | Cited 6 times

Online Publication Date: 30 May 2012

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We studied the spatial and temporal distributions of ionic, neutral, and molecular species generated by femtosecond laser produced plasma under varying ambient nitrogen gas pressures. Plasmas were generated by irradiating planar graphite targets using 40 fs pulses of 800 nm radiation from a Ti:Sapphire laser. The results show that in the presence of an ambient gas, the molecular species spatial extension and lifetime are directly correlated to the evolution of excited ions. The present studies also provide valuable insights into the evolution history of various species and their excitation during ultrafast laser ablation.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Nature of optical transitions involving cation vacancies and complexes in AlN and AlGaN

A. Sedhain, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 100, 221107 (2012); http://dx.doi.org/10.1063/1.4723693 (4 pages)

Online Publication Date: 30 May 2012

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Photoluminescence spectroscopy was employed to probe the nature of optical transitions involving Al vacancy (VAl) and vacancy-oxygen complex (VAl-ON) in AlN. An emission line near 2 eV due to the recombination between the 2− charge state of (VAl-ON)2−/1−, and the valence band was directly observed under a below bandgap excitation scheme. This photoluminescence (PL) band was further resolved into two emission lines at 1.9 and 2.1 eV, due to the anisotropic binding energies of VAl-ON complex caused by two different bonding configurations–the substitutional ON sits along c-axis or sits on one of the three equivalent tetrahedral positions. Moreover, under an above bandgap excitation scheme, a donor-acceptor pair like transition involving shallow donors and (VAl-ON)2−/1− deep acceptors, which is the “yellow-luminescence” band counterpart in AlN, was also seen to split into two emission lines at 3.884 and 4.026 eV for the same physical reason. Together with previous results, a more complete picture for the optical transitions involving cation vacancy related deep centers in AlGaN alloy system has been constructed.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
61.72.jd Vacancies
71.20.Ps Other inorganic compounds

Enhanced optical limiting in nanosized mixed zinc ferrites

Panit Chantharasupawong, Reji Philip, Tamio Endo, and Jayan Thomas

Appl. Phys. Lett. 100, 221108 (2012); http://dx.doi.org/10.1063/1.4724194 (4 pages) | Cited 3 times

Online Publication Date: 30 May 2012

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Optical limiting performance of zinc ferrite, nickel zinc ferrite, and copper zinc ferrite nanoparticles is investigated at 532 nm using 5 nanosecond laser pulses. Enhanced optical limiting is observed in the mixed zinc ferrites, which is attributed to the relative longevity of self-trapped charge transfer states. Samples exhibit absorption saturation followed by a rapid onset of optical limiting as the input fluence is increased. This is advantageous in applications where detector sensitivity should be retained at the maximum value until the input fluence approaches the detector damage regime. The Z-scan results are compared to those measured in C60.
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42.79.-e Optical elements, devices, and systems
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Mechanism of electron acceleration by chirped laser pulse

X. Y. Wu, P. X. Wang, and S. Kawata

Appl. Phys. Lett. 100, 221109 (2012); http://dx.doi.org/10.1063/1.4723847 (4 pages) | Cited 2 times

Online Publication Date: 31 May 2012

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We studied the mechanism of electron acceleration by a chirped laser pulse. We found that, because of the chirp effect, a region exists where the laser wave phase experienced by the electron varies slowly, so that the electron can be accelerated for a long time. The mechanism of chirped laser acceleration is different to that of the capture and acceleration scenario, although both of them have a main acceleration stage in which the electrons are trapped for long periods.
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41.75.Fr Electron and positron beams
42.62.-b Laser applications
42.60.Fc Modulation, tuning, and mode locking

Photonic crystal tunable slow light device integrated with multi-heaters

Norihiro Ishikura, Ryo Hosoi, Ryo Hayakawa, Takemasa Tamanuki, Mizuki Shinkawa, and Toshihiko Baba

Appl. Phys. Lett. 100, 221110 (2012); http://dx.doi.org/10.1063/1.4724191 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2012

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We fabricated photonic crystal slow light waveguides integrated with multi-heaters, using CMOS-compatible process. By optimizing heating powers and adjusting the index distribution, a clear delay peak was observed, which suggests that the fabrication errors were compensated for completely. When a linear index chirp was added to this condition, the delay was tuned by 54 ps. When a quadratic chirp was added, arbitrary group delay dispersion was generated at wavelengths around 1550 nm within a 3 nm bandwidth. The continuously tunable range was from −32 to 54 ps/nm/mm. Using this as a dispersion compensator, we compressed pre-chirped pico-second pulses.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer

Surface plasmon polariton-controlled tunable quantum-dot emission

R. J. Moerland, H. T. Rekola, G. Sharma, A.-P. Eskelinen, A. I. Väkeväinen, and P. Törmä

Appl. Phys. Lett. 100, 221111 (2012); http://dx.doi.org/10.1063/1.4724327 (4 pages) | Cited 2 times

Online Publication Date: 1 June 2012

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The unique properties of surface plasmon polaritons, such as strong field confinement and local field enhancement effects, make them ideal candidates to enhance and shape the emission of luminescent nanoparticles. Of these nanoparticles, quantum dots are highly versatile, suitable for vastly different applications due to their size and material tunability. In many cases however, the emission wavelength of the quantum dots is fixed after manufacturing, allowing no control over the in situ emission properties. Here, we show fully optical, in situ tunability of the emission wavelength of quantum dots, with shifts of over 30 nm, employing surface plasmon polaritons to control the emission wavelength.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.22.Lp Collective excitations
73.21.La Quantum dots
78.55.-m Photoluminescence, properties and materials
78.67.Hc Quantum dots
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