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7 Mar 2011

Volume 98, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 98, 104101 (2011); http://dx.doi.org/10.1063/1.3560505 (3 pages)

Zhongchang Wang, Susumu Tsukimoto, Rong Sun, Mitsuhiro Saito, and Yuichi Ikuhara
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Vertical subwavelength mode confinement in terahertz and mid-infrared quantum cascade lasers

E. Strupiechonski, D. Grassani, D. Fowler, F. H. Julien, S. P. Khanna, L. Li, E. H. Linfield, A. G. Davies, A. B. Krysa, and R. Colombelli

Appl. Phys. Lett. 98, 101101 (2011); http://dx.doi.org/10.1063/1.3560980 (3 pages) | Cited 4 times

Online Publication Date: 7 March 2011

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We exploit the modal confinement properties of metal-metal ridge waveguides to investigate the effect of reducing the thickness of the active laser cores in both terahertz and mid-infrared quantum cascade lasers. Devices with active regions over 55 times thinner than the free-space emission wavelength are demonstrated. They show only a modest increase in threshold current density compared with conventional-thickness devices. The limited increase in threshold is possibly due to a parasitic current channel in addition to the radiative current channel. These structures could be useful for the development of ultra-low volume lasers.
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42.50.Pq Cavity quantum electrodynamics; micromasers
42.60.By Design of specific laser systems
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
42.55.Px Semiconductor lasers; laser diodes

Gain enhancement in a terahertz quantum cascade laser with parylene antireflection coatings

R. Rungsawang, N. Jukam, J. Maysonnave, P. Cavalié, J. Madéo, D. Oustinov, S. S. Dhillon, J. Tignon, P. Gellie, C. Sirtori, S. Barbieri, H. E. Beere, and D. A. Ritchie

Appl. Phys. Lett. 98, 101102 (2011); http://dx.doi.org/10.1063/1.3562002 (3 pages) | Cited 3 times

Online Publication Date: 7 March 2011

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We study the effect of parylene antireflection coatings on the gain of a 2.8 THz quantum cascade laser using terahertz time-domain spectroscopy. With antireflection coatings the threshold current increases as the mirror losses are increased, and the gain clamps at 16 cm−1, compared to 10 cm−1 for an uncoated device. These values are consistent with a drop in reflectivity from 0.320 to 0.053 as a consequence of the coating deposition. Further improvements could reveal the bare cavity gain and permit the quantum cascade laser to be used as an efficient terahertz amplifier.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Wc Optical coatings
42.79.Bh Lenses, prisms and mirrors
42.70.Jk Polymers and organics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Reaction-controlled diffraction grating of photopolymer for use of phase stable holographic optical element

Yong-Cheol Jeong, Bokyung Jung, Jihye Lee, and Jung-Ki Park

Appl. Phys. Lett. 98, 101103 (2011); http://dx.doi.org/10.1063/1.3562032 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2011

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Herein we propose control of polymerization kinetics to prevent inherent scattering problem of holographic photopolymer system that is caused by a phase separation between matrix and photopolymerized grating polymers. To elucidate this, in this letter, phase stability of the photopolymer system was studied with molecular dynamic simulation of Flory–Huggins theory and was investigated in the respect of polymerization kinetics. It was controlled with the variables of monomer conversion and degree of polymerization by varying both reaction time and rates. In addition, volume grating fixing effect of post ultraviolet treatment on photopolymer was examined.
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42.70.Jk Polymers and organics
82.35.-x Polymers: properties; reactions; polymerization
42.40.Eq Holographic optical elements; holographic gratings

Pencil lead plasma for generating multimicrojoule high-order harmonics with a broad spectrum

Y. Pertot, L. B. Elouga Bom, V. R. Bhardwaj, and T. Ozaki

Appl. Phys. Lett. 98, 101104 (2011); http://dx.doi.org/10.1063/1.3558999 (3 pages) | Cited 6 times

Online Publication Date: 9 March 2011

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Using the plasma harmonic method, we show the generation of efficient and intense high-order harmonics from plasma of pencil lead. We demonstrate multimicrojoule energy in each harmonic order for the 11th to the 17th order of a Ti:sapphire laser. By analyzing the target morphology and the plasma composition, we conclude that these intense harmonics are generated from nanoparticles of graphitic carbon.
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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
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Modeling the lasing spectra of InAs/InP Quantum dash lasers

M. Z. M. Khan, T. K. Ng, U. Schwingenschlogl, P. Bhattacharya, and B. S. Ooi

Appl. Phys. Lett. 98, 101105 (2011); http://dx.doi.org/10.1063/1.3560052 (3 pages) | Cited 1 time

Online Publication Date: 9 March 2011

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We report a theoretical model for InAs/InP quantum-dash (Qdash) lasers incorporating a coupled set of rate equations taking into account the inhomogeneous broadening due to Qdash size fluctuation, the homogeneous broadening due to optical gain of a single Qdash, and the longitudinal cavity modes. The role of cavity length on the Qdash lasing characteristics, particularly the redshift in the peak lasing wavelength, is analyzed and compared with the experimental results by attributing it to the active region inhomogeneity.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Biaxial tensile strain effects on photoluminescence of different orientated Ge wafers

H.-S. Lan, S.-T. Chan, T.-H. Cheng, C.-Y. Chen, S.-R. Jan, and C. W. Liu

Appl. Phys. Lett. 98, 101106 (2011); http://dx.doi.org/10.1063/1.3562589 (3 pages) | Cited 5 times

Online Publication Date: 9 March 2011

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The enhanced photoluminescence of direct transition is observed on (100), (110), and (111) Ge under biaxial tensile strain. The enhancement is caused by the increase in electron population in the Γ valley. The shrinkage of energy difference between the lowest L valleys and the Γ valley is responsible to the population increase on (100) and (110) Ge. For (111) Ge, the energy difference increases under biaxial tensile strain but the strain decreases energy difference between the electron quasi-Fermi level and the Γ valley due to the small density of state of the lowest L valleys, and thus enhances direct recombination.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High-speed nanometer-resolved imaging vibrometer and velocimeter

Ata Mahjoubfar, Keisuke Goda, Ali Ayazi, Ali Fard, Sang Hyup Kim, and Bahram Jalali

Appl. Phys. Lett. 98, 101107 (2011); http://dx.doi.org/10.1063/1.3563707 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2011

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Conventional laser vibrometers are incapable of performing multidimensional vibrometry at high speeds because they build on single-point measurements and rely on beam scanning, significantly limiting their utility and precision. Here we introduce a laser vibrometer that performs high-speed multidimensional imaging-based vibration and velocity measurements with nanometer-scale axial resolution without the need for beam scanning. As a proof-of-concept, we demonstrate real-time microscopic imaging of acoustic vibrations with 1 nm axial resolution, 1200 image pixels, and 30 ps dwell time at 36.7 MHz scan rate.
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07.10.-h Mechanical instruments and equipment
06.60.Jn High-speed techniques (microsecond to femtosecond)
06.30.Gv Velocity, acceleration, and rotation

Ultrafast cross saturation dynamics in inhomogeneously broadened InAs/InP quantum dash optical amplifiers

A. Capua, G. Eisenstein, and J. P. Reithmaier

Appl. Phys. Lett. 98, 101108 (2011); http://dx.doi.org/10.1063/1.3564901 (3 pages) | Cited 2 times

Online Publication Date: 10 March 2011

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We describe multiwavelength pump probe characterization of an inhomogeneously broadened semiconductor nanostructure gain medium. An InAs/InP quantum-dash optical amplifier is perturbed by a 100 fs pulse and the response is measured at wavelengths outside the homogeneously broadened spectral region. Energy dependent carrier cross relaxation as well as capture and escape processes are investigated and quantified.
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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

Experimental cross-polarization detection of coupling far-field light to highly confined plasmonic gap modes via nanoantennas

J. Wen, P. Banzer, A. Kriesch, D. Ploss, B. Schmauss, and U. Peschel

Appl. Phys. Lett. 98, 101109 (2011); http://dx.doi.org/10.1063/1.3564904 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2011

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We experimentally demonstrate the coupling of far-field light to highly confined plasmonic gap modes via connected nanoantennas. The excitation of plasmonic gap modes is shown to depend on the polarization, position, and wavelength of the incident beam. Far-field measurements performed in crossed polarization allow for the detection of extremely weak signals re-emitted from gap waveguides and can increase the signal-to-noise ratio dramatically.
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73.22.Lp Collective excitations
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)

Theoretical study of polarization-doped GaN-based light-emitting diodes

L. Zhang, K. Ding, N. X. Liu, T. B. Wei, X. L. Ji, P. Ma, J. C. Yan, J. X. Wang, Y. P. Zeng, and J. M. Li

Appl. Phys. Lett. 98, 101110 (2011); http://dx.doi.org/10.1063/1.3565173 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2011

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Insufficient hole injection is a major impediment to the luminescence efficiency of III-nitride light-emitting diodes (LEDs). In our previous work by Zhang et al. [Appl. Phys. Lett. 97, 062103 (2010)] , high-density mobile three-dimensional hole gas is obtained in Mg-doped Al composition graded AlGaN layer with Al composition linearly decreasing from a certain value to 0. In this paper, it is revealed by a theoretical study that the hole injection efficiency in blue-light GaN-based LEDs can be greatly enhanced by using this polarization-doped method. An increase in the electroluminescence intensity and the internal quantum efficiency in polarization-doped GaN-based LEDs is observed, in comparison with a conventional LED.
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85.60.Jb Light-emitting devices
85.30.Kk Junction diodes

Multiple Bragg diffraction in magnetophotonic crystals

Seungmin Baek, Alexander V. Baryshev, and Mitsuteru Inoue

Appl. Phys. Lett. 98, 101111 (2011); http://dx.doi.org/10.1063/1.3560256 (3 pages) | Cited 1 time

Online Publication Date: 11 March 2011

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We demonstrate properties of magnetophotonic crystals (MPCs) with quasi-two-dimensional structure. Crystals were bismuth-substituted yttrium iron garnet/silicon dioxide (Bi:YIG/SiO2) multilayers sputtered on top of one-dimensional structured substrates. Parameters of these MPCs were such that two spectrally neighboring stop bands overlapped in their spectra. For MPCs in this multiple Bragg diffraction regime, we observed a strong dispersion of their magneto-optical responses—an enhancement of the polarization rotation and an alteration of the rotation sign.
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42.79.Dj Gratings
42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Ls Magneto-optical effects
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