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13 Oct 2008

Volume 93, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 93, 151101 (2008); http://dx.doi.org/10.1063/1.2996271 (3 pages)

Xuefeng Zeng and Hongrui Jiang
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Tunable liquid microlens actuated by infrared light-responsive hydrogel

Xuefeng Zeng and Hongrui Jiang

Appl. Phys. Lett. 93, 151101 (2008); http://dx.doi.org/10.1063/1.2996271 (3 pages) | Cited 19 times

Online Publication Date: 13 October 2008

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We report on liquid-based tunable microlenses actuated by infrared (IR) light. Multiple micropost structures, made of IR light-responsive hydrogel with entrapped gold nanoparticles, are photopatterned around a lens aperture. The volumetric change in the hydrogel, controlled by IR light, regulates the curvature of a liquid-liquid interface forming the microlens at the aperture and its focal length. The focal length of the microlens can be tuned from −17.4 mm to +8.0±0.4 mm in seconds under IR irradiation. This microlens can be integrated into optical systems, for instance, for fiber endoscopy.
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42.79.Bh Lenses, prisms and mirrors

Enhancement of third harmonic generation by a laser-induced plasma

Klaus Hartinger and Randy A. Bartels

Appl. Phys. Lett. 93, 151102 (2008); http://dx.doi.org/10.1063/1.2993222 (3 pages) | Cited 7 times

Online Publication Date: 13 October 2008

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We demonstrate more than two orders of magnitude in enhancement of conversion of an ultrafast probe pulse to the third harmonic that is time delayed with respect to a pump pulse. The enhancement is observed in various atomic and molecular gases over a range of pressures.
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52.38.-r Laser-plasma interactions
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

A monolithic optical sensor based on whispering-gallery modes in polystyrene microspheres

Julie Lutti, Wolfgang Langbein, and Paola Borri

Appl. Phys. Lett. 93, 151103 (2008); http://dx.doi.org/10.1063/1.2998652 (3 pages) | Cited 4 times

Online Publication Date: 13 October 2008

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We experimentally demonstrate a monolithic sensor based on sharp whispering-gallery optical resonances of polystyrene microspheres in water attached onto an optical coupler via a solid separation layer index matched to water. A Q-factor of 0.9×106 is measured on a microsphere of 44 μm diameter with a 650 nm thick separation layer. As a proof of principle of the sensing capabilities, we measure the response to refractive index changes and infer a shot-noise limited precision of 1×10−8 refractive index units.
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42.70.Jk Polymers and organics
42.79.Pw Imaging detectors and sensors

Direct laser writing of three-dimensional photonic structures in Nd:yttrium aluminum garnet laser ceramics

Airán Ródenas, Guangyong Zhou, Daniel Jaque, and Min Gu

Appl. Phys. Lett. 93, 151104 (2008); http://dx.doi.org/10.1063/1.2998258 (3 pages) | Cited 6 times

Online Publication Date: 14 October 2008

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We report on the direct laser writing of a three-dimensional photonic structure in a neodymium doped yttrium aluminum garnet laser ceramic. The fabricated structure consists of a voxel-based face centered cubic lattice showing a stop band centered at 2.4 μm. Confocal luminescence imaging was used to study the submicron low refractive-index voxels constituting the photonic structure, as well as to elucidate how the luminescence properties of the neodymium laser ions are modified by the writing process.
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42.70.Qs Photonic bandgap materials
42.62.-b Laser applications
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Hx Other solid inorganic materials
61.66.Fn Inorganic compounds
42.55.Rz Doped-insulator lasers and other solid state lasers

Visible red random lasing in Y2O3:Eu3+/ZnO polycrystalline thin films by energy transfer from ZnO films to Eu3+

M. K. Chong, A. P. Abiyasa, K. Pita, and S. F. Yu

Appl. Phys. Lett. 93, 151105 (2008); http://dx.doi.org/10.1063/1.2993340 (3 pages) | Cited 17 times

Online Publication Date: 14 October 2008

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Visible red random lasing centered at ∼ 611 nm has been observed in Y2O3:Eu3+/ZnO films at room temperature. Using a 355 nm laser source to excite the ZnO films, ultraviolet (UV) random lasing has been observed. The UV lasing spectrum can be tuned to overlap strongly with the 7F0-5L6 excitation spectrum of Eu3+ ions centered at ∼ 394 nm by controlling the pump power, leading to very efficient radiative energy transfer from the ZnO films to Eu3+ ions. As a result, a red random lasing centered at ∼ 611 nm corresponding to the 5D0-7F2 transition of Eu3+ ions was observed.
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42.55.Rz Doped-insulator lasers and other solid state lasers
33.80.Be Level crossing and optical pumping

Ultrafast phase-resolved pump-probe measurements on a quantum cascade laser

W. Kuehn, W. Parz, P. Gaal, K. Reimann, M. Woerner, T. Elsaesser, T. Müller, J. Darmo, K. Unterrainer, M. Austerer, G. Strasser, L. R. Wilson, J. W. Cockburn, A. B. Krysa, and J. S. Roberts

Appl. Phys. Lett. 93, 151106 (2008); http://dx.doi.org/10.1063/1.2998648 (3 pages) | Cited 3 times

Online Publication Date: 14 October 2008

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The dynamics of optical gain in an InGaAs/AlInAs quantum cascade laser is studied in midinfrared pump-probe measurements. Pump and probe pulses of identical wavelength, polarization, and propagation direction through the laser waveguide are detected separately by electro-optic sampling. For injection currents below the lasing threshold, we observe an absorption decrease in the laser transition with a ≈ 3 ps recovery time. Above threshold, the gain strongly saturates and shows a fast recovery time decreasing with current. Such kinetics is superimposed by oscillations with a frequency of 0.8 THz originating from coherent electron tunneling through the injection barrier.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
84.40.Az Waveguides, transmission lines, striplines
73.40.Gk Tunneling

Direct evidence of trap-mediated excitation in GaN:Er3+ with a two-color experiment

Loic Bodiou and Alain Braud

Appl. Phys. Lett. 93, 151107 (2008); http://dx.doi.org/10.1063/1.2999585 (3 pages)

Online Publication Date: 14 October 2008

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We report a direct confirmation of the generally proposed rare-earth excitation model in GaN. The intermediate step involving the formation of excitons bound to rare-earth ions prior to the rare-earth excitation is demonstrated. Using a two-color experiment, we show that the erbium photoluminescence decay following a pulsed laser excitation is quenched when an additional continuous-wave (cw) laser is applied. As the two beams excite the sample, the cw beam perturbs the intermediate step of the Er excitation mechanism either by photoionization of Er-related trapped carriers or by inducing an Auger effect between the trapped carriers and free carriers.
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78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena

Implementation scheme for quantum controlled phase-flip gate through quantum dot in slow-light photonic crystal waveguide

Jie Gao, F. W. Sun, and Chee Wei Wong

Appl. Phys. Lett. 93, 151108 (2008); http://dx.doi.org/10.1063/1.2999588 (3 pages) | Cited 7 times

Online Publication Date: 14 October 2008

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We propose a scheme to realize controlled phase gate between two single photons through a single quantum dot in a slow-light photonic crystal waveguide. Enhanced Purcell factor and large β-factor lead to high gate fidelity over broadband frequencies compared to cavity-assisted system. The excellent physical integration of this photonic crystal waveguide system provides tremendous potential for large-scale quantum information processing.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
03.67.Lx Quantum computation architectures and implementations

Glass supported ZnSe microring strongly coupled to a single CdSe quantum dot

Johannes Renner, Lukas Worschech, Alfred Forchel, Suddhasatta Mahapatra, and Karl Brunner

Appl. Phys. Lett. 93, 151109 (2008); http://dx.doi.org/10.1063/1.2998403 (3 pages) | Cited 5 times

Online Publication Date: 15 October 2008

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By means of molecular beam epitaxy a single layer of self-assembled CdSe quantum dots (QDs) embedded in a ZnSe/ZnMgSSe heterostructure was grown on a GaAs substrate. Electron beam lithography and etching techniques were then applied to pattern microrings. Afterward the microstructures were glued on a glass support and the GaAs was totally removed. The photoluminescence of such glass supported rings was studied for different temperatures, and tuning of single QD lines into resonance with a cavity photon mode was achieved. Strong coupling was found with a Rabi splitting of 0.7 meV attributed to the strong oscillator strength of CdSe quantum dots.
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81.05.Dz II-VI semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
81.65.Cf Surface cleaning, etching, patterning

Nanomaterial enabled laser transfer for organic light emitting material direct writing

Seung H. Ko, Heng Pan, Sang G. Ryu, Nipun Misra, Costas. P. Grigoropoulos, and Hee K. Park

Appl. Phys. Lett. 93, 151110 (2008); http://dx.doi.org/10.1063/1.3001803 (3 pages) | Cited 15 times

Online Publication Date: 15 October 2008

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Organic light emitting material direct writing is demonstrated based on nanomaterial enabled laser transfer. Through utilization of proper nanoparticle size and type and the laser wavelength choice, a single laser pulse could transfer well-defined and arbitrarily shaped tris-(8-hydroxyquinoline)Al patterns ranging from several microns to millimeter size. The unique properties of nanomaterials allow laser induced forward transfer at low laser energy (0.05 J/cm2) while maintaining good fluorescence. The technique may be well suited for the mass production of temperature sensitive organic light emitting devices.
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85.60.Jb Light-emitting devices

Sixfold symmetry of excitonic transition energies in c-plane for wurtzite GaN

Guo-Dong Hao, Y. H. Chen, and Y. F. Hao

Appl. Phys. Lett. 93, 151111 (2008); http://dx.doi.org/10.1063/1.3001937 (3 pages) | Cited 1 time

Online Publication Date: 15 October 2008

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The optical properties of the strained wurtzite GaN are investigated theoretically within the nearest neighbor tight-binding method. The piezoelectric effect is also taken into account. The empirical rule has been used in the strained band-structure calculation. The results show that the excitonic transition energies are anisotropic in the c-plane in a high electronic concentration system and have a 60° periodicity, which is in agreement with experiment.
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71.35.-y Excitons and related phenomena
71.20.Nr Semiconductor compounds
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.65.-j Piezoelectricity and electromechanical effects
61.50.-f Structure of bulk crystals

Evidence of “crossed” transitions in dots-in-a-well structures through waveguide absorption measurements

G. Visimberga, G. Rainò, A. Salhi, V. Tasco, M. T. Todaro, L. Martiradonna, M. De Giorgi, A. Passaseo, R. Cingolani, and M. De Vittorio

Appl. Phys. Lett. 93, 151112 (2008); http://dx.doi.org/10.1063/1.3000381 (3 pages) | Cited 6 times

Online Publication Date: 16 October 2008

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In-plane absorption measurements were performed at room temperature by means of a waveguide transmission setup on a Stranski–Krastanov InAs dots-in-a-well system emitting at 1.3 μm embedded in a p-i-n structure. The polarization dependence of quantum dot (QD) absorption was exploited to resolve its discrete and continuous spectral components and study them separately under reverse bias application. The quantum confined Stark effect observed in the discrete spectral component gave evidence of an upward built-in QD dipole of about 9.5×10−29 C m. The continuous component was found to originate from electronic transitions involving a QD state and a quantum well state.
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68.65.Fg Quantum wells
68.65.Hb Quantum dots (patterned in quantum wells)
78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects

Laser drilling induced electrical type inversion in vacancy-doped p-type HgCdTe

F. X. Zha, S. M. Zhou, H. L. Ma, F. Yin, B. Zhang, T. X. Li, J. Shao, and X. C. Shen

Appl. Phys. Lett. 93, 151113 (2008); http://dx.doi.org/10.1063/1.3001930 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2008

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Femtosecond laser was used to generate micrometer-sized holes in vacancy-doped p type mercury cadmium telluride (HgCdTe). Characterization by laser beam induced current (LBIC) microscope shows obvious electrical type inversion around each hole. Both the intensity of the LBIC signals and the spatial dimension of the type-inversed regions are well comparable with those of n-on-p HgCdTe photodiodes formed by the conventional ion milling technique. The observation demonstrates the potential of laser drilling to be a new tool in fabricating HgCdTe photodiode arrays.
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72.40.+w Photoconduction and photovoltaic effects
42.62.Cf Industrial applications
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
61.72.jd Vacancies
85.60.Dw Photodiodes; phototransistors; photoresistors

Control of broad-area vertical-cavity surface emitting laser emission by optically induced photonic crystals

Bernd Terhalle, Neal Radwell, Patrick Rose, Cornelia Denz, and Thorsten Ackemann

Appl. Phys. Lett. 93, 151114 (2008); http://dx.doi.org/10.1063/1.2996257 (3 pages) | Cited 7 times

Online Publication Date: 17 October 2008

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We control the emission properties of a broad-area vertical-cavity surface emitting laser by coupling it to an external feedback cavity containing a photorefractive crystal with an optically induced photonic lattice. The periodic modulation of the refractive index serves as a tunable filter and enables the dynamic suppression of unwanted spatial instabilities and modes, as originally suggested by Gomila et al. [Phys. Rev. Lett. 92, 253904 (2004)].
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Ci Filters, zone plates, and polarizers

Distribution of point defects in orientation-patterned GaAs crystals: A cathodoluminescence study

D. Faye, A. Grisard, E. Lallier, B. Gérard, M. Avella, and J. Jimenez

Appl. Phys. Lett. 93, 151115 (2008); http://dx.doi.org/10.1063/1.2999586 (3 pages) | Cited 3 times

Online Publication Date: 17 October 2008

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Toward efficient generation of tunable IR signals by quasi-phase-matched nonlinear optical frequency conversion, orientation-patterned GaAs crystals (OP-GaAs) were grown by hydride vapor phase epitaxy on lithographically prepared templates. The cathodoluminescence technique was used to study these epitaxial thick films, consisting of periodic domains of inverted crystallographic orientation, (001)/(00−1). The distribution of the main defects incorporated during growth is presented. One demonstrates that point defects, such as VGa complexes, can contribute to the optical losses of thick OP-GaAs crystals.
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61.72.jn Color centers
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.66.Fd III-V semiconductors
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Electroluminescence from silicon-rich nitride/silicon superlattice structures

J. Warga, R. Li, S. N. Basu, and L. Dal Negro

Appl. Phys. Lett. 93, 151116 (2008); http://dx.doi.org/10.1063/1.3003867 (3 pages) | Cited 30 times

Online Publication Date: 17 October 2008

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Luminescent silicon-rich nitride/silicon superlattice structures (SRN/Si-SLs) with different silicon concentrations were fabricated by direct magnetron cosputtering deposition. Rapid thermal annealing at 700 °C resulted in the nucleation of small amorphous Si clusters that emit at 800 nm under both optical and electrical excitations. The electrical transport mechanism and the electroluminescence (EL) of SRN/Si-SLs have been investigated. Devices with low turn-on voltage (6 V) have been demonstrated and the EL mechanism has been attributed to bipolar recombination of electron-hole pairs at Si nanoclusters. Our results demonstrate that amorphous Si clusters in SRN/Si-SLs provide a promising route for the fabrication of Si-compatible optical devices.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.60.Fi Electroluminescence
78.55.Ap Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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