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6 Oct 2008

Volume 93, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 93, 141901 (2008); http://dx.doi.org/10.1063/1.2990662 (3 pages)

J. H. Han, K. B. Kim, S. Yi, J. M. Park, S. W. Sohn, T. E. Kim, D. H. Kim, J. Das, and J. Eckert
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Ionic liquid as additive to increase sensitivity, resolution, and diffraction efficiency of photopolymerizable hologram material

Hechun Lin, Peter W. Oliveira, and Michael Veith

Appl. Phys. Lett. 93, 141101 (2008); http://dx.doi.org/10.1063/1.2995851 (3 pages) | Cited 5 times

Online Publication Date: 6 October 2008

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Ionic liquid was used as additive in photosensitive photopolymerizable materials. Ionic liquid as additive in photopolymerizable hologram material increases the sensitivity, the resolution, and the refractive index modulation of the material efficiently, which present strong diffusion after stopping the exposure due to the diffusion-controlled polymerization in ionic liquid. The diffraction efficiency was raised up to the theoretical maximum of 34% in the thin hologram.
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42.40.Eq Holographic optical elements; holographic gratings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.35.-x Polymers: properties; reactions; polymerization
42.70.Jk Polymers and organics
42.70.Ln Holographic recording materials; optical storage media

Enhanced high-gain harmonic generation for x-ray free-electron laser

Qika Jia

Appl. Phys. Lett. 93, 141102 (2008); http://dx.doi.org/10.1063/1.2993179 (3 pages) | Cited 8 times

Online Publication Date: 7 October 2008

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The harmonic generation free-electron laser (HG-FEL) is capable of producing temporally and spatially coherent pulses in the vacuum ultraviolet and shorter wavelength regions. In this letter an easy-to-implement scheme that significantly enhances the performance of HG-FEL and extends its short-wavelength range is proposed. By adding a short phase-reversed modulator after the dispersive section, the electron energy spread is reduced and simultaneously the electron microbunching is enhanced. Three-dimensional simulations demonstrate the energy spread reduction and the bunching enhancement and show that more powerful higher harmonic radiation can be obtained.
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41.60.Cr Free-electron lasers
42.55.Vc X- and γ-ray lasers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Intersubband linewidths in quantum cascade laser designs

A. Wittmann, Y. Bonetti, J. Faist, E. Gini, and M. Giovannini

Appl. Phys. Lett. 93, 141103 (2008); http://dx.doi.org/10.1063/1.2993212 (3 pages) | Cited 24 times

Online Publication Date: 7 October 2008

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We present a model to a priori calculate the temperature and field dependent intersubband linewidth of the optical transition in quantum cascade laser designs. Besides intra- and intersubband lifetime broadening, it comprises interface roughness scattering based on the approach of Tsujino et al. [Appl. Phys. Lett. 86, 062113 (2005) ]. We verified our model with experimental data of quantum cascade lasers having different linewidths. Excellent agreement with the experiment was found for the two-phonon resonance design. Linewidths are slightly overestimated in the bound-to-continuum design. Differential gain and threshold current density are in excellent agreement for the two-phonon resonance design. Although the slope efficiency is somewhat underestimated at low temperatures, there is still reasonable agreement with the experiment.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Beryllium acceptor binding energy in AlN

A. Sedhain, T. M. Al Tahtamouni, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 93, 141104 (2008); http://dx.doi.org/10.1063/1.2996977 (3 pages) | Cited 1 time

Online Publication Date: 7 October 2008

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The acceptor binding energy of an alternative dopant, Be, in AlN epilayers has been probed by time-resolved photoluminescence (PL) spectroscopy. The binding energy of excitons bound to Be acceptors in AlN is determined to be about 33 meV, which implies that the Be acceptor binding energy in AlN is about 0.33 eV in accordance with Haynes’ rule. The measured PL decay lifetimes of the acceptor-bound exciton transitions in Be- and Mg-doped AlN (93 and 119 ps, respectively) also indicate that the binding energy of Be acceptor is smaller than that of the most common acceptor dopant in AlN, namely, Mg. The smaller activation energy of Be in AlN has the potential to partly address the critical p-type doping issue in AlN- and Al-rich AlGaN by increasing the room temperature free hole concentration by ∼ 103 compared to the case of Mg doping.
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71.55.Eq III-V semiconductors
71.35.-y Excitons and related phenomena
61.72.uj III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Coherent trapping of x-ray photons in crystal cavities in the picosecond regime

S.-Y. Chen, H.-H. Wu, Y.-Y. Chang, Y.-R. Lee, W.-H. Sun, S.-L. Chang, Yu. P. Stetsko, M.-T. Tang, M. Yabashi, and T. Ishikawa

Appl. Phys. Lett. 93, 141105 (2008); http://dx.doi.org/10.1063/1.2996275 (3 pages) | Cited 1 time

Online Publication Date: 7 October 2008

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We report on the trapping of 14 keV photons in periods of 1.11–1.67 ps by the 12 4 0 backdiffraction in two- and multiplate silicon single-crystal cavities of a few hundred micrometer size. The formation of standing waves inside the cavities ensures better coherence for the x rays. We anticipate that the transmitted x rays through this type of cavities can be used as a quasicoherent x-ray source for probing the dynamic structures of solids, liquids, and biological substances.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.85.-m X- and γ-ray instruments

Highly efficient low-voltage cathodoluminescence of LaF3:Ln3+ (Ln = Eu3+,Ce3+,Tb3+) spherical particles

Zhen-Ling Wang, H. L. W. Chan, Hiu-Ling Li, and J. H. Hao

Appl. Phys. Lett. 93, 141106 (2008); http://dx.doi.org/10.1063/1.2998582 (3 pages) | Cited 40 times

Online Publication Date: 8 October 2008

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Spherical particles of rare-earth doped LaF3 are synthesized through refluxing in glycerol/water media. The low-voltage cathodoluminescence of LaF3:Eu due to 5D0→7F1 and 5D0→7F2 transitions was found to be sensitive to the site that Eu3+ ions occupied. The luminous efficiency of LaF3:Ce3+, Tb3+ with green emission is improved from 1.53 to 2.02 lm/W compared with LaF3:Tb3+, due to the energy transfer processes from Ce3+ to Tb3+ ions. Our results suggest that the obtained spherical particles of rare-earth doped LaF3 are promising as highly efficient low-voltage cathodoluminescent phosphors, which have received considerably less attention.
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78.60.Hk Cathodoluminescence, ionoluminescence

Fiber laser pumped high average power single-cycle terahertz pulse source

Matthias C. Hoffmann, Ka-Lo Yeh, Harold Y. Hwang, Thomas S. Sosnowski, Bradley S. Prall, János Hebling, and Keith A. Nelson

Appl. Phys. Lett. 93, 141107 (2008); http://dx.doi.org/10.1063/1.2998609 (3 pages) | Cited 13 times

Online Publication Date: 9 October 2008

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Near single-cycle terahertz pulse generation from lithium niobate crystal by optical rectification of pulses from an Yb:fiber laser/amplifier system was investigated. The pump laser supplied 250 fs duration pulses with 14 μJ energy at up to 1 MHz repetition rate. The terahertz pulse energy and average power exceeded 0.25 nJ and 0.25 mW, respectively. The average power was more than ten times higher than corresponding values achieved by using GaP as the nonlinear crystal under similar pumping conditions.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Terahertz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer in a pulse tube cooler

H. Richter, A. D. Semenov, S. G. Pavlov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, K. S. Il’in, M. Siegel, and H.-W. Hübers

Appl. Phys. Lett. 93, 141108 (2008); http://dx.doi.org/10.1063/1.2988896 (3 pages) | Cited 20 times

Online Publication Date: 10 October 2008

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A liquid cryogen-free terahertz heterodyne receiver in a pulse tube cooler has been realized. The receiver operates at 2.5 THz. It is based on a quantum cascade laser (QCL) as local oscillator and a hot electron bolometric mixer. A detailed study of the QCL beam quality yielded a beam propagation factor of 1.1–1.2. The double sideband noise temperature of the system is 2000 K and when corrected for optical losses in the signal path it is ∼ 800 K.
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42.55.Px Semiconductor lasers; laser diodes
42.79.-e Optical elements, devices, and systems
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Terahertz surface plasmon polaritons on a helically grooved wire

A. I. Fernández-Domínguez, C. R. Williams, F. J. García-Vidal, L. Martín-Moreno, S. R. Andrews, and S. A. Maier

Appl. Phys. Lett. 93, 141109 (2008); http://dx.doi.org/10.1063/1.2988897 (3 pages) | Cited 9 times

Online Publication Date: 10 October 2008

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The propagation of tightly confined terahertz surface plasmon polaritons on a helically grooved metal wire has been studied both experimentally and theoretically. The periodic structure of such metawires allows the formation of surface electromagnetic modes with different azimuthal symmetry at wavelengths longer than the pitch. There is good agreement between the experimentally determined band edge frequencies of these modes and numerical calculations for the structure investigated.
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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)
78.68.+m Optical properties of surfaces
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