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4 Aug 2008

Volume 93, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 93, 051101 (2008); http://dx.doi.org/10.1063/1.2965797 (3 pages)

Mariano A. Zimmler, Jiming Bao, Federico Capasso, Sven Müller, and Carsten Ronning
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Laser action in nanowires: Observation of the transition from amplified spontaneous emission to laser oscillation

Mariano A. Zimmler, Jiming Bao, Federico Capasso, Sven Müller, and Carsten Ronning

Appl. Phys. Lett. 93, 051101 (2008); http://dx.doi.org/10.1063/1.2965797 (3 pages) | Cited 64 times

Online Publication Date: 4 August 2008

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Direct evidence of the transition from amplified spontaneous emission to laser action in optically pumped zinc oxide (ZnO) nanowires, at room temperature, is presented. The optical power evolves from a superlinear to a linear regime as the pump power exceeds threshold, concomitant with a transition to directional emission along the nanowire and the emergence of well defined cavity Fabry–Pérot modes around a wavelength of ≈ 385 nm, the intensity of which exceeds the spontaneous emission background by orders of magnitude. The laser oscillation threshold is found to be strongly dependent on nanowire diameter, with no laser oscillation observed for diameters smaller than ∼ 150 nm. Finally, we use an alternative “head on” detection geometry to measure the output power of a single nanowire laser.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Room temperature polariton lasing in a GaN/AlGaN multiple quantum well microcavity

Gabriel Christmann, Raphaël Butté, Eric Feltin, Jean-François Carlin, and Nicolas Grandjean

Appl. Phys. Lett. 93, 051102 (2008); http://dx.doi.org/10.1063/1.2966369 (3 pages) | Cited 67 times

Online Publication Date: 4 August 2008

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The authors report room temperature polariton lasing at λ ∼ 345 nm in a hybrid AlInN/AlGaN multiple quantum well microcavity (MQW-MC) containing a GaN/AlGaN MQW active region, i.e., the achievement under nonresonant optical excitation of coherent light emission of a macroscopic population of polaritons occupying the lowest energy state of the lower polariton branch. This was made possible by taking advantage of the efficient relaxation of polaritons in a MQW-MC exhibiting a large vacuum Rabi splitting ΩVRS = 56 meV.
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78.67.De Quantum wells
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.21.Fg Quantum wells

Extreme-ultraviolet frequency comb generation by polarization-gated surface-enhanced optical fields

Jian Wu, Hongxing Qi, and Heping Zeng

Appl. Phys. Lett. 93, 051103 (2008); http://dx.doi.org/10.1063/1.2967732 (3 pages) | Cited 3 times

Online Publication Date: 4 August 2008

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We show that two synchronized counter-propagating femtosecond pulses could be controlled by adjusting their relative delay to excite surface-enhanced optical fields of time-gated linear polarization in contrast with intrinsic elliptic polarization excited by the conventional one-pulse incidence scheme. Such surface-enhanced optical fields can be used to generate efficient high harmonics and thus extreme-ultraviolet frequency combs. The energy conversion efficiency as well as the frequency span of the generated extreme-ultraviolet frequency combs can be significantly increased with controllable emission probabilities along different directions relative to the surface.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Temperature-stable operation of a quantum dot semiconductor disk laser

T. D. Germann, A. Strittmatter, J. Pohl, U. W. Pohl, D. Bimberg, J. Rautiainen, M. Guina, and O. G. Okhotnikov

Appl. Phys. Lett. 93, 051104 (2008); http://dx.doi.org/10.1063/1.2968137 (3 pages) | Cited 15 times

Online Publication Date: 5 August 2008

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We demonstrate temperature-independent output characteristics of an optically pumped semiconductor disk laser (SDL) based on quantum dots (QDs) grown in the Stranski-Krastanow regime. The gain structure consists of a stack of 7×3 QD layers, each threefold group being located at an optical antinode position. The SDL emits at 1210 nm independent of the pump power density. Threshold and differential efficiency do not dependent on heat sink temperature. Continuous-wave operation close to 300 mW output power is achieved using the ground-state transition of the InGaAs QDs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Terahertz conductivity of thin metal films

N. Laman and D. Grischkowsky

Appl. Phys. Lett. 93, 051105 (2008); http://dx.doi.org/10.1063/1.2968308 (3 pages) | Cited 13 times

Online Publication Date: 5 August 2008

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The conductivities of thin Al, Au, and Ag films were measured via their transmission at terahertz frequencies. The conductivities of all the films, particularly the thinner films and Al films, were much smaller than their bulk dc values. This reduced conductivity can be quantitatively understood in terms of an increased scattering rate from defects. The transmission is consistent with a frequency independent conductivity, implying a very fast electron scattering time.
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73.61.At Metal and metallic alloys

Enhancement of surface plasmon-mediated radiative energy transfer through a corrugated metal cathode in organic light-emitting devices

Jing Feng, Takayuki Okamoto, Ryo Naraoka, and Satoshi Kawata

Appl. Phys. Lett. 93, 051106 (2008); http://dx.doi.org/10.1063/1.2968309 (3 pages) | Cited 15 times

Online Publication Date: 5 August 2008

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We report enhanced top emission from organic light-emitting devices by surface plasmon-mediated radiative energy transfer. A dye-doped dielectric acceptor layer was deposited onto the surface of a one-dimensionally corrugated silver cathode and was excited by the electroluminescence of a donor layer, which is located at the other side of the cathode. Ten times enhancement in emission intensity from the acceptor was observed compared to flat devices; this is due to the enhanced radiative energy transfer from the donor to the acceptor by the coupled surface plasmons on the opposite interfaces of the silver cathode.
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85.60.Jb Light-emitting devices
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.45.Fk Electrodes

Laser microfabrication and rotation of ship-in-a-bottle optical rotators

Shigeki Matsuo, Satoshi Kiyama, Yoshinori Shichijo, Takuro Tomita, Shuichi Hashimoto, Yoichiroh Hosokawa, and Hiroshi Masuhara

Appl. Phys. Lett. 93, 051107 (2008); http://dx.doi.org/10.1063/1.2967872 (3 pages) | Cited 8 times

Online Publication Date: 5 August 2008

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We have fabricated optical rotators inside a silica substrate and rotated them by a laser trapping technique. The fabrication method used was femtosecond laser-assisted etching, i.e., modification of the host material by irradiation with femtosecond laser pulses along a predesigned pattern, followed by selective chemical etching. The rotators, which consist of the same material as the substrate, can move inside the microcavity but cannot get out. The rotation speed was proportional to the trapping laser power, and the maximum achieved was about 100 rpm. Such rotators will be applicable to micro-total-analysis systems and microfluidics.
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81.65.Cf Surface cleaning, etching, patterning
33.55.+b Optical activity and dichroism
81.16.Ta Atom manipulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Amplification of transition-Cherenkov terahertz radiation of femtosecond filament in air

Yi Liu, Aurélien Houard, Bernard Prade, André Mysyrowicz, Abdourahmane Diaw, and Vladimir T. Tikhonchuk

Appl. Phys. Lett. 93, 051108 (2008); http://dx.doi.org/10.1063/1.2965612 (3 pages) | Cited 5 times

Online Publication Date: 5 August 2008

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The transition-Cherenkov terahertz radiation from a femtosecond laser filament in air is enhanced by three orders of magnitude in the presence of a longitudinal static electric field, while the radiation pattern and the polarization remain the same. An amplified longitudinal electron current inside the filament is responsible for this amplified terahertz emission.
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52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Control of the gated spectra with narrow bandwidth from a supercontinuum using ultrafast optical Kerr gate of bismuth glass

Wenjiang Tan, Hui Liu, Jinhai Si, and Xun Hou

Appl. Phys. Lett. 93, 051109 (2008); http://dx.doi.org/10.1063/1.2968202 (3 pages) | Cited 8 times

Online Publication Date: 6 August 2008

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Supercontinuum generation and its application have become one of the attractive research fields in ultrafast optics. We have acquired a series of narrow bandwidth and symmetric gated spectra continuously from the chirped supercontinuum generated in a sapphire plate with a femtosecond laser, using an ultrafast optical Kerr gate (OKG) with Bi2O3–B2O3–SiO2 oxide glass as the Kerr material. Experimental results show that the gated spectra obtained using OKG of the glass have more superiorities comparing with CS2.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Ce Glasses, quartz
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

40 GHz small-signal cross-gain modulation in 1.3 μm quantum dot semiconductor optical amplifiers

C. Meuer, J. Kim, M. Laemmlin, S. Liebich, D. Bimberg, A. Capua, G. Eisenstein, R. Bonk, T. Vallaitis, J. Leuthold, A. R. Kovsh, and I. L. Krestnikov

Appl. Phys. Lett. 93, 051110 (2008); http://dx.doi.org/10.1063/1.2969060 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2008

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Small-signal cross-gain modulation of quantum dot based semiconductor optical amplifiers (QD SOAs), having a dot-in-a-well structure, is presented, demonstrating superiority for ultrahigh bit rate wavelength conversion. Optimization of the QD SOA high speed characteristics via bias current and optical pump power is presented and a small-signal 3 dB bandwidth exceeding 40 GHz is demonstrated. The p-doped samples investigated here enable small-signal wavelength conversion within a range of 30 nm, limited mainly by the gain bandwidth.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots
42.65.-k Nonlinear optics

An experimental study of the interactions of self-trapped white light beams in a photopolymer

Kailash Kasala and Kalaichelvi Saravanamuttu

Appl. Phys. Lett. 93, 051111 (2008); http://dx.doi.org/10.1063/1.2957994 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2008

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Interactions of two parallel-propagating and mutually incoherent white light beams were examined in a photopolymerizable organosiloxane. The beams fused when separated by a distance corresponding to the width of each beam but at separation distances⪢beam width, formed two self-trapped beams that repelled each other. At separation distances<beam width, they suffered filamentation but ultimately fused into a single self-trapped beam.
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42.70.Jk Polymers and organics
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Photoinduced microchannels inside silicon by femtosecond pulses

Tao Chen, Jinhai Si, Xun Hou, Shingo Kanehira, Kiyotaka Miura, and Kazuyuki Hirao

Appl. Phys. Lett. 93, 051112 (2008); http://dx.doi.org/10.1063/1.2969401 (3 pages) | Cited 9 times

Online Publication Date: 7 August 2008

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We reported on the fabrication of microchannels in the interior of silicon wafers using a femtosecond laser of 800 nm wavelength, which was in the absorption region of silicon. The scanning electron micrographs showed that microchannels were induced inside the silicon wafer when the femtosecond laser beam was focused inside the wafer. The aspect ratio of the microchannel cross section decreased with the increase in scan velocity of the laser. The formation of the photoinduced microchannels probably resulted from the microexplosions due to both the linear absorption and avalanche ionization.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Migration enhanced lateral epitaxial overgrowth of AlN and AlGaN for high reliability deep ultraviolet light emitting diodes

R. Jain, W. Sun, J. Yang, M. Shatalov, X. Hu, A. Sattu, A. Lunev, J. Deng, I. Shturm, Y. Bilenko, R. Gaska, and M. S. Shur

Appl. Phys. Lett. 93, 051113 (2008); http://dx.doi.org/10.1063/1.2969402 (3 pages) | Cited 9 times

Online Publication Date: 7 August 2008

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We report on the growth of low-defect thick films of AlN and AlGaN on trenched AlGaN/sapphire templates using migration enhanced lateral epitaxial overgrowth. Incoherent coalescence-related defects were alleviated by controlling the tilt angle of growth fronts and by allowing Al adatoms sufficient residence time to incorporate at the most energetically favorable lattice sites. Deep ultraviolet light emitting diode structures (310 nm) deposited over fully coalesced thick AlN films exhibited cw output power of 1.6 mW at 50 mA current with extrapolated lifetime in excess of 5000 hours. The results demonstrate substantial improvement in the device lifetime, primarily due to the reduced density of growth defects.
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85.60.Jb Light-emitting devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors

Light amplification by stimulated Raman scattering in AlGaAs-based photonic-crystal line-defect waveguides

Hisaya Oda, Kuon Inoue, Akio Yamanaka, Naoki Ikeda, Yoshimasa Sugimoto, and Kiyoshi Asakawa

Appl. Phys. Lett. 93, 051114 (2008); http://dx.doi.org/10.1063/1.2965110 (3 pages) | Cited 14 times

Online Publication Date: 7 August 2008

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The authors performed an amplification experiment of optical signal around 1550 nm by stimulated Raman scattering in a photonic-crystal slab waveguide (WG) of single-line defect. They adopted an air-bridge type AlGaAs-based WG sample to avoid two-photon absorption. Short light pulses of 5 ps in duration operated at 20 MHz and a cw laser were employed for pump (excitation) and probe (signal) lights, respectively. As a result, amplification of a net gain of ∼ 3 dB (maximum) is achieved with pulse pump energy of 22 pJ for a sample of 1.0 mm in length.
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42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.82.Et Waveguides, couplers, and arrays
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Spectral optimization of phosphor-conversion light-emitting diodes for ultimate color rendering

A. Žukauskas, R. Vaicekauskas, F. Ivanauskas, H. Vaitkevičius, and M. S. Shur

Appl. Phys. Lett. 93, 051115 (2008); http://dx.doi.org/10.1063/1.2966150 (3 pages) | Cited 14 times

Online Publication Date: 8 August 2008

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We apply an optimization scheme based on rendering of all colors of the enhanced Munsell palette to phosphor-conversion (PC) light-emitting diodes (LEDs). This approach yields combinations of peak wavelengths and bandwidths for white PC LEDs with partial and complete conversion that enable lighting with better quality than that obtained using designs based on the standard color-rendering assessment procedure.
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85.60.Jb Light-emitting devices

Ultrafast spin noise spectroscopy

Sebastian Starosielec and Daniel Hägele

Appl. Phys. Lett. 93, 051116 (2008); http://dx.doi.org/10.1063/1.2969041 (3 pages) | Cited 6 times

Online Publication Date: 8 August 2008

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We propose an extension of optical spin noise spectroscopy that expands the so far accessible frequency range from a few gigahertz to several terahertz employing pairs of ultrafast femtosecond-laser pulses. The method is suitable for probing noise signals with very high bandwidths and signals centered at zero frequency. A time-resolved version of noise spectroscopy for detecting noise after a pump event follows naturally from the scheme. The analytical description of ultrafast spin noise spectroscopy along with numerical simulations proves the method a powerful spectroscopic tool.
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78.47.D- Time resolved spectroscopy (>1 psec)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Transmission measurement of the photonic band gap of GaN photonic crystal slabs

J. Caro, E. M. Roeling, B. Rong, Hoang M. Nguyen, E. W. J. M. van der Drift, S. Rogge, F. Karouta, R. W. van der Heijden, and H. W. M. Salemink

Appl. Phys. Lett. 93, 051117 (2008); http://dx.doi.org/10.1063/1.2967744 (3 pages) | Cited 1 time

Online Publication Date: 8 August 2008

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A high-contrast-ratio (30 dB) photonic band gap in the near-infrared transmission of hole-type GaN two-dimensional photonic crystals (PhCs) is reported. These crystals are deeply etched in a 650 nm thick GaN layer grown on sapphire. A comparison of the measured spectrum with finite difference time domain simulations gives quantitative agreement for the dielectric band and qualitative agreement for the air band. The particular behavior of the air band arises from the relatively low index contrast between the GaN layer and the sapphire substrate. Our results call for extension of the operation of GaN PhCs to the visible range.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning
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