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14 Jan 2008

Volume 92, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 022509 (2008); http://dx.doi.org/10.1063/1.2807274 (3 pages)

Sang-Koog Kim, Ki-Suk Lee, Young-Sang Yu, and Youn-Seok Choi
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Physical properties and efficiency of GaNP light emitting diodes

J. Chamings, S. Ahmed, S. J. Sweeney, V. A. Odnoblyudov, and C. W. Tu

Appl. Phys. Lett. 92, 021101 (2008); http://dx.doi.org/10.1063/1.2830696 (3 pages) | Cited 6 times

Online Publication Date: 14 January 2008

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GaNP/GaP is promising for yellow-amber-red light emitting diodes (LEDs). In this study, pressure and temperature dependent electroluminescence and photocurrent measurements on bulk GaP/GaN0.006P0.994/GaP LED structures are presented. Below ∼ 110 K, emission is observed from several localized nitrogen states. At room temperature, the band-edge energy increases weakly with pressure at a rate of +1.6 meV/kbar, substantially lower than the Γ band gap of GaP (+9.5 meV/kbar). Thus, despite the multiplicity of nitrogen levels, the band anticrossing model reasonably describes this system based on an average of the nitrogen states. Furthermore, carrier leakage into the X minima of GaP reduces the efficiency in GaNP-LEDs with increasing pressure.
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85.60.Jb Light-emitting devices

Time-resolved photoluminescence of n-doped SrTiO3

A. Rubano, D. Paparo, M. Radović, A. Sambri, F. Miletto Granozio, U. Scotti di Uccio, and L. Marrucci

Appl. Phys. Lett. 92, 021102 (2008); http://dx.doi.org/10.1063/1.2832666 (3 pages) | Cited 7 times

Online Publication Date: 14 January 2008

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Following the recent surge of interest in n-doped strontium titanate as a possible blue light emitter, a time-resolved photoluminescence analysis was performed on nominally pure, Nb-doped and oxygen-deficient single-crystal SrTiO3 samples. The doping effects on both the electronic states involved in the transition and the decay mechanism are respectively analyzed by comparing the spectral and dynamic features and the yields of the emission. Our time-resolved analysis, besides shedding some light on the basic recombination mechanisms acting in these materials, sets the intrinsic bandwidth limit of the proposed blue light emitting optoelectronic devices made of Ti-based perovskites heterostructures in the gigahertz range.
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78.55.Hx Other solid inorganic materials
78.47.jd Time resolved luminescence

Measurement of semiconductor waveguide optical properties in the midinfrared wavelength range

E. Peter, S. Laurent, C. Sirtori, M. Carras, J. A. Robbo, M. Garcia, and X. Marcadet

Appl. Phys. Lett. 92, 021103 (2008); http://dx.doi.org/10.1063/1.2830829 (3 pages) | Cited 2 times

Online Publication Date: 14 January 2008

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We propose a technique based on Fabry-Pérot fringes to analyze, in a broad wavelength range, the waveguide properties of semiconductor lasers in the midinfrared spectrum. This technique has been applied to strain-balanced Ga0.32In0.68As/Al0.64In0.36As quantum cascade lasers, with a double phonon active region, in order to determine propagation losses and the effective index between 2.5 and 8 μm wavelength. These results are in good agreement with the values obtained using another method.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
07.60.Ly Interferometers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Self-sustained output power pulsations in InGaAs quantum dot ridge-waveguide lasers

S. Mokkapati, H. H. Tan, C. Jagadish, and M. Buda

Appl. Phys. Lett. 92, 021104 (2008); http://dx.doi.org/10.1063/1.2830998 (3 pages) | Cited 2 times

Online Publication Date: 14 January 2008

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Self-sustained pulsations in the output power of metal-organic chemical vapor deposition grown ridge-waveguide lasers with InGaAs quantum dot active region are reported. The characteristics of the output power pulsations (range, frequency, and modulation depth) are presented. The origin of the pulsations is explained in terms of the properties of the quantum dot active region.
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84.40.Az Waveguides, transmission lines, striplines
42.55.Px Semiconductor lasers; laser diodes

A Sn-based metal substrate technology for the fabrication of vertical-structured GaN-based light-emitting diodes

Hon-Yi Kuo, Shui-Jinn Wang, Pei-Ren Wang, Kai-Ming Uang, Tron-Min Chen, and Hon Kuan

Appl. Phys. Lett. 92, 021105 (2008); http://dx.doi.org/10.1063/1.2834373 (3 pages) | Cited 6 times

Online Publication Date: 14 January 2008

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Through the use of tin (Sn) based solder balls and patterned laser lift-off technique, a metal substrate technology was proposed for the fabrication of vertical-structured metal substrate GaN-based light-emitting diodes (VM-LEDs). Advantages including reserving the merits of metallic substrate and simplifying the fabrication processes of vertical-structured GaN-based LEDs were demonstrated. As compared to conventional sapphire substrate GaN-based LEDs, the fabricated VM-LEDs with an emission area of 620×620 μm2 show an increase in light output power about 145.36% at 350 mA with a significant decrease in forward voltage from 4.51 to 3.46 V.
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85.60.Jb Light-emitting devices

Fast photorefractive self-focusing in InP:Fe semiconductor at infrared wavelengths

Delphine Wolfersberger, Naïma Khelfaoui, Cristian Dan, Nicolas Fressengeas, and Hervé Leblond

Appl. Phys. Lett. 92, 021106 (2008); http://dx.doi.org/10.1063/1.2830989 (3 pages) | Cited 5 times

Online Publication Date: 14 January 2008

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Photorefractive beam self-trapping is investigated in InP:Fe and is shown to occur within tens of microseconds after beam switch on. This fast response time is predicted by an analytical theoretical interpretation based on a simple photorefraction model which suggests buildups in a time range consistent with experiments.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

The Christiansen effect in terahertz time-domain spectra of coarse-grained powders

Morten Franz, Bernd M. Fischer, and Markus Walther

Appl. Phys. Lett. 92, 021107 (2008); http://dx.doi.org/10.1063/1.2831910 (3 pages) | Cited 23 times

Online Publication Date: 14 January 2008

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Spectral distortions are commonly observed in terahertz transmission spectra of ground substances immersed in a transparent host medium. This effect originates from scattering due to the index contrast between the grains and diluent. A phenomenological expression quantitatively accounts for the scattering induced attenuation and the phase delay experienced by the electric field transmitted through the sample. Based on the knowledge of the refractive indices of the sample and the host material, we present a procedure to eliminate the scattering contribution from the absorption spectra.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.70.Gq Microwave and radio-frequency interactions
61.43.Gt Powders, porous materials

Photonic crystal nanolaser monolithically integrated with passive waveguide for effective light extraction

Kengo Nozaki, Hideki Watanabe, and Toshihiko Baba

Appl. Phys. Lett. 92, 021108 (2008); http://dx.doi.org/10.1063/1.2831916 (3 pages) | Cited 27 times

Online Publication Date: 14 January 2008

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We recently reported room-temperature continuous-wave operation in a GaInAsP photonic crystal slab nanolaser. In this letter, we demonstrate effective light extraction from the nanolaser monolithically integrated with a passive waveguide by using a GaInAsP butt-joint regrowth technique. Theoretically, the extraction efficiency through the waveguide was calculated to be 80% for the optimum design of the coupling system of the nanolaser and the waveguide. In the experiment, we evaluated a differential quantum efficiency of 4%, which was degraded mainly due to the detection loss of the output light.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
81.05.Ea III-V semiconductors

Very low transparency currents in double quantum well InGaAs semiconductor lasers with δ-doped resonant tunneling

D. Fekete, M. Yasin, A. Rudra, and E. Kapon

Appl. Phys. Lett. 92, 021109 (2008); http://dx.doi.org/10.1063/1.2825465 (3 pages) | Cited 2 times

Online Publication Date: 14 January 2008

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It is demonstrated that n-type δ-doped resonant tunneling double quantum well (QW) lasers operated close to resonance exhibit an extremely low transparency current density of 14 A/cm2 per QW. This suggests that the threshold current is almost identical to that of the best reported single QW device without δ doping and yet the modal gain is almost double. The low transparency current density is mainly due to the enhanced coupling between the QWs.
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71.55.Eq III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes
85.75.Mm Spin polarized resonant tunnel junctions

Active waveguide in Nd3+:MgO:LiNbO3 crystal produced by low-dose carbon ion implantation

Feng Chen, Yang Tan, Daniel Jaque, Lei Wang, Xue-Lin Wang, and Ke-Ming Wang

Appl. Phys. Lett. 92, 021110 (2008); http://dx.doi.org/10.1063/1.2832767 (3 pages) | Cited 9 times

Online Publication Date: 15 January 2008

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We report on Nd3+:MgO:LiNbO3 active planar waveguides produced by 3 MeV carbon ion implantation at dose of 7.5×1014 cm−2. The extraordinary refractive index of the sample surface experiences positive alternations after the implantation and subsequent thermal annealing treatment, constructing enhanced-well confined waveguide structures. The propagation loss of the waveguide is 1–2 dB/cm, which means acceptable quality for further guide-wave applications. The microluminescence spectra of the waveguide show fairly good potentials for laser action at 929 and 1085 nm.
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42.79.Gn Optical waveguides and couplers
81.40.Gh Other heat and thermomechanical treatments
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays

Bright, low voltage europium doped gallium oxide thin film electroluminescent devices

P. Wellenius, A. Suresh, and J. F. Muth

Appl. Phys. Lett. 92, 021111 (2008); http://dx.doi.org/10.1063/1.2824846 (3 pages) | Cited 16 times

Online Publication Date: 15 January 2008

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Europium doped gallium oxide thin film electroluminescent devices with bright, red emission (611 nm) and relatively low threshold voltages of 60 V were produced using pulsed laser deposition. The use of transparent conducting electrodes of amorphous InGaZnO on transparent aluminum titanium oxide/indium tin oxide/7059 Corning glass substrates resulted in a device that is transparent throughout the visible spectrum. At 100 V, with 1 kHz excitation, the luminance was 221 cd/m2. The Sawyer-Tower circuit analysis and time dependent emission measurements suggest that the charge trapping at the aluminum titanium oxide/Ga2O3:Eu interface plays an important role in producing efficient emission.
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85.60.Jb Light-emitting devices
81.15.Fg Pulsed laser ablation deposition

Single-mode octagonal photonic crystal fibers for the middle infrared

Arnon Millo, Lilya Lobachinsky, and Abraham Katzir

Appl. Phys. Lett. 92, 021112 (2008); http://dx.doi.org/10.1063/1.2829885 (3 pages) | Cited 9 times

Online Publication Date: 15 January 2008

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Single-mode optical fibers for the middle infrared are needed for many applications such as infrared fiber lasers, spatial filtering, and interferometry. Index guiding photonic crystal fibers offer many advantages over regular step-index fibers such as a wide spectral range and large core area. In this paper, we report the design and fabrication of single-mode octagonal photonic crystal fibers. These fibers were fabricated from silver halide polycrystalline materials which have high transmission in the middle infrared. The fibers showed a single-mode behavior at 10.6 μm with low losses and a large mode diameter (110 μm).
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42.81.Bm Fabrication, cladding, and splicing
42.81.Dp Propagation, scattering, and losses; solitons
42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design

Luminescence enhancement by Si ring resonator structures on silicon on insulator

Shiyun Lin, Yosuke Kobayashi, Yasuhiko Ishikawa, and Kazumi Wada

Appl. Phys. Lett. 92, 021113 (2008); http://dx.doi.org/10.1063/1.2835051 (3 pages) | Cited 4 times

Online Publication Date: 15 January 2008

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Si ring resonators on silicon on insulator show at least 50 times stronger photoluminescence (PL) with sharp peaks than the surrounding Si slab region at room temperature. The frequencies of the PL peaks are well explained by the resonant frequencies of the rings and the intensities are by the ratio of the quality factors of the PL peaks and the modal volumes of resonances. This suggests that the Purcell effect should be responsible for the enhancement.
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42.79.-e Optical elements, devices, and systems
42.82.-m Integrated optics

The use of combination of nonlinear optical materials to control terahertz pulse generation and detection

M. M. Nazarov, S. A. Makarova, A. P. Shkurinov, and O. G. Okhotnikov

Appl. Phys. Lett. 92, 021114 (2008); http://dx.doi.org/10.1063/1.2831658 (3 pages) | Cited 4 times

Online Publication Date: 16 January 2008

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We suggest composite nonlinear optical media based on the pair of ZnTe and GaP crystals for terahertz pulse detection or generation. The influence of laser wavelength, pulse duration, and media thickness on the terahertz pulse conversion are studied. The optimization of the composite structure performed numerically allowed for essential improvement of the phase-matching condition observed in the experiment.
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81.05.Ea III-V semiconductors
81.05.Dz II-VI semiconductors
42.70.Mp Nonlinear optical crystals
42.65.-k Nonlinear optics
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources

Single-walled carbon nanotubes for high-energy optical pulse formation

Yong-Won Song, Shinji Yamashita, and Shigeo Maruyama

Appl. Phys. Lett. 92, 021115 (2008); http://dx.doi.org/10.1063/1.2834898 (3 pages) | Cited 45 times

Online Publication Date: 16 January 2008

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We passively generate picosecond 6.5 nJ optical pulses directly from a single-stage oscillator using carbon nanotube mode locker. The mode locker immunized to the high optical power induced damage employs the evanescent field interaction of propagating light with the nanotubes. The mode locker endures the intracavity power of up to 27.7 dBm. For the enhanced interaction, vertically aligned nanotubes are synthesized and applied. The output pulses are monitored for 200 h to find that there is no significant degradation of average power and spectral width.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Shaping tight-focusing patterns of linearly polarized beams through elliptic apertures

Taro Ando, Yoshiyuki Ohtake, Takashi Inoue, Haruyasu Itoh, Naoya Matsumoto, and Norihiro Fukuchi

Appl. Phys. Lett. 92, 021116 (2008); http://dx.doi.org/10.1063/1.2834899 (3 pages)

Online Publication Date: 16 January 2008

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We propose elliptic deformation of apertures for shaping focusing patterns of tightly focused linearly polarized beams. Numerical integration of the vectorial Rayleigh-Sommerfeld diffraction formula predicts the formation of symmetric focusing patterns by shrinking the aperture shape in the direction perpendicular to the polarization of the beams. The elliptic deformation is also applied to a focused linearly polarized beam through an annular aperture to demonstrate the formation of smaller symmetric focal spot than that through a simple oval aperture.
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42.25.Ja Polarization

Controlled thermal emission of polarized infrared waves from arrayed plasmon nanocavities

K. Ikeda, H. T. Miyazaki, T. Kasaya, K. Yamamoto, Y. Inoue, K. Fujimura, T. Kanakugi, M. Okada, K. Hatade, and S. Kitagawa

Appl. Phys. Lett. 92, 021117 (2008); http://dx.doi.org/10.1063/1.2834903 (3 pages) | Cited 20 times

Online Publication Date: 16 January 2008

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We have demonstrated thermal emission of linearly polarized and narrow-band midinfrared waves from subwavelength gratings of narrow and deep rectangular cavities engraved on a Au surface. 100-nm-wide and 1000-nm-deep, high-aspect trenches were accurately manufactured by inversion from master molds. Organ pipe resonance of surface plasmons in the cavities exhibits a Lorentzian emission peak centered at 2.5–5.5 μm. The maximum emittance reaches 0.90 and the peak width Δλ/λ is as narrow as 0.13–0.23. This simple emitter is expected to play a key role in the infrared sensing technologies for analyzing our environment.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Stimulated emission and lasing from an Al0.13Ga0.87N/GaN double heterostructure grown on a silicon substrate

F. S. Al-Ajmi, R. M. Kolbas, J. C. Roberts, P. Rajagopal, J. W. Cook, Jr., E. L. Piner, and K. J. Linthicum

Appl. Phys. Lett. 92, 021118 (2008); http://dx.doi.org/10.1063/1.2819614 (3 pages)

Online Publication Date: 17 January 2008

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Stimulated emission and laser action with well developed longitudinal optical modes from an Al0.13Ga0.87N/GaN double heterostructure with a 25 nm GaN active layer grown on a silicon substrate by metal-organic chemical vapor deposition is demonstrated. Lasing was observed from cleaved platelets at room temperature with well resolved Fabry-Pérot modes at a wavelength as short as 368 nm at room temperature. A clear threshold was observed in the plot of the emission intensity versus the pumping power at both 77 K and room temperature. The effective index of refraction during laser operation was measured to be 2.65.
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78.66.Fd III-V semiconductors
78.45.+h Stimulated emission
42.55.Px Semiconductor lasers; laser diodes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

A frequency-selective circulator via mode coupling between surface waveguide and resonators

A. Q. Liu, E. H. Khoo, T. H. Cheng, E. P. Li, and J. Li

Appl. Phys. Lett. 92, 021119 (2008); http://dx.doi.org/10.1063/1.2830838 (3 pages) | Cited 5 times

Online Publication Date: 17 January 2008

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In this letter, a frequency-selective circulator via mode coupling between a circular photonic crystal (CPC) surface waveguide and resonator systems is developed. The curve surface waveguide is formed by reducing the outermost rods radii. It has a transmission efficiency of 95% when the surface concentric distance is reduced by half. The resonator system, which consists of rod(s) are placed at each of the CPC perpendicular axis. Using optimized resonator physical parameters, selected frequencies are dropped at different locations with efficiency of 97%. It is suggested that several circulators can be cascaded to build a large scale frequency-selective multiplexing system.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Long-term stabilized two-beam combination laser amplifier with stimulated Brillouin scattering mirrors

Hong Jin Kong, Jin Woo Yoon, Jae Sung Shin, and Du Hyun Beak

Appl. Phys. Lett. 92, 021120 (2008); http://dx.doi.org/10.1063/1.2831659 (3 pages) | Cited 10 times

Online Publication Date: 17 January 2008

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The beam combination method is the promising technique for constructing a very high energy laser with a high repetition rate over 10 Hz such as a real fusion driver. In our previous works, the phase control technique essential for realizing this system was proposed and demonstrated experimentally. However, these previous works were done without amplifiers. In this work, we employed amplifiers to test the real beam combination system and obtained a well stabilized phase controlling with λ/51 fluctuation by standard deviation during 5000 laser shots (500 s) at 204 mJ total output energy.
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42.65.Es Stimulated Brillouin and Rayleigh scattering
42.79.-e Optical elements, devices, and systems

Paraxial energy transport of a focused Gaussian beam in ruby with nondegenerate two-wave couplinglike mechanism

Feng Gao, Jingjun Xu, Guoquan Zhang, Fang Bo, and Haixu Liu

Appl. Phys. Lett. 92, 021121 (2008); http://dx.doi.org/10.1063/1.2827568 (3 pages) | Cited 5 times

Online Publication Date: 17 January 2008

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Paraxial energy transport of an intensity-modulated and focused Gaussian beam is studied in ruby. Deformations of the temporal profiles are observed under different conditions and explained by the interplay among a nondegenerate two-wave couplinglike mechanism, the population oscillations, and the Fraunhofer diffraction. Experimental evidence is provided for the existence of a nondegenerate two-wave couplinglike mechanism. The self-superluminal can be observed under proper conditions. A group velocity of −83 m/s is achieved with a Gaussian-like-modulated pulse of 30 ms with background illumination. Based on these results, a method to control the group velocity of a single beam in such media is proposed.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Room-temperature intracavity difference-frequency generation in butt-joint diode lasers

B. N. Zvonkov, A. A. Biryukov, A. V. Ershov, S. M. Nekorkin, V. Ya. Aleshkin, V. I. Gavrilenko, A. A. Dubinov, K. V. Maremyanin, S. V. Morozov, A. A. Belyanin, V. V. Kocharovsky, and Vl. V. Kocharovsky

Appl. Phys. Lett. 92, 021122 (2008); http://dx.doi.org/10.1063/1.2835048 (3 pages) | Cited 6 times

Online Publication Date: 17 January 2008

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We observe room-temperature intracavity difference-frequency generation in the mid-infrared range in a butt-joint GaAs/InGaAs/InGaP quantum-well laser diode which supports lasing at two closely spaced wavelengths in the near-infrared range around 1 μm. We employ a special asymmetric waveguide design and a low-doped substrate that minimize midinfrared losses and phase mismatch for the difference-frequency generation process.
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42.55.Px Semiconductor lasers; laser diodes
85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.67.De Quantum wells

Thermal annealing effects on intersubband transitions in (CdS/ZnSe)/BeTe quantum wells

B. S. Li, R. Akimoto, and A. Shen

Appl. Phys. Lett. 92, 021123 (2008); http://dx.doi.org/10.1063/1.2835050 (3 pages) | Cited 2 times

Online Publication Date: 17 January 2008

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The authors report the study of thermal annealing effects on intersubband transition (ISB-T) properties of (CdS/ZnSe)/BeTe quantum wells (QWs). With the increase of annealing temperature, the ISB absorption wavelength shifts to lower energy and absorption intensity gradually decreases. The dependence of linewidths on the annealing temperature is more complicated and shows opposite trends for the QWs with different well thicknesses. Photoinduced ISB-T measurements indicate that the decrease of ISB absorption intensity results from the loss of free carriers in the well layers. The change of structural properties obtained from x-ray diffraction measurements were used to explain the observed change of ISB absorption characteristics.
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78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Tv Optical and dielectric properties related to treatment conditions
68.65.Fg Quantum wells

Simulated [111] Si–SiGe terahertz quantum cascade laser

L. Lever, A. Valavanis, Z. Ikonić, and R. W. Kelsall

Appl. Phys. Lett. 92, 021124 (2008); http://dx.doi.org/10.1063/1.2836023 (3 pages) | Cited 7 times

Online Publication Date: 18 January 2008

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The prospect of developing a silicon laser has long been an elusive goal, mainly due to the indirect band gap and large effective carrier masses. We present a design for a terahertz intersubband laser grown on the [111] crystal plane and simulate performance using a rate equation method including scattering due to alloy disorder, interface roughness, carrier-phonon, and Coulombic interactions. We predict gain greater than 40 cm−1 and a threshold current density of 70 A/cm2.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
68.35.Ct Interface structure and roughness
63.20.kd Phonon-electron interactions

Generation of submicrojoule high harmonics using a long gas jet in a two-color laser field

I Jong Kim, Gae Hwang Lee, Seung Beom Park, Yong Soo Lee, Tae Keun Kim, Chang Hee Nam, Tomas Mocek, and Krzysztof Jakubczak

Appl. Phys. Lett. 92, 021125 (2008); http://dx.doi.org/10.1063/1.2836252 (3 pages) | Cited 34 times

Online Publication Date: 18 January 2008

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We have achieved very efficient high-harmonic generation in a two-color laser field using a long gas jet of He. With the optimization of laser parameters and target conditions, strong harmonics were produced at 2(2n+1)th orders in an orthogonally polarized two-color field. The strongest harmonic at the 38th order (21.6 nm) reached an energy of 0.6 μJ with a 6 mm gas jet, giving a conversion efficiency as high as 2×10−4.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
51.70.+f Optical and dielectric properties
32.80.-t Photoionization and excitation
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