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25 Apr 2005

Volume 86, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 86, 173508 (2005); http://dx.doi.org/10.1063/1.1914966 (3 pages)

A. M. Clark, N. A. Miller, A. Williams, S. T. Ruggiero, G. C. Hilton, L. R. Vale, J. A. Beall, K. D. Irwin, and J. N. Ullom
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Ultralow-power all-optical switching

Marin Soljačić, Elefterios Lidorikis, J. D. Joannopoulos, and Lene Vestergaard Hau

Appl. Phys. Lett. 86, 171101 (2005); http://dx.doi.org/10.1063/1.1900956 (3 pages) | Cited 32 times

Online Publication Date: 18 April 2005

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Using analytical modeling and detailed numerical simulations, we investigate properties of hybrid systems of photonic crystal microcavities which incorporate a highly nonlinear ultraSlow light medium. We demonstrate that such systems, while being miniature in size (order wavelength), and integrable, could enable ultrafast nonlinear all-optical switching at ultralow (even single photon) energy levels.
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42.70.Qs Photonic bandgap materials
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Optical observation of donor-bound excitons in hydrogen-implanted ZnO

J.-K. Lee, M. Nastasi, D. W. Hamby, and D. A. Lucca

Appl. Phys. Lett. 86, 171102 (2005); http://dx.doi.org/10.1063/1.1906330 (3 pages) | Cited 10 times

Online Publication Date: 18 April 2005

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The optical and structural properties of H or He implanted ZnO were investigated using low temperature photoluminescence (PL) and infrared spectroscopy (IR). H implantation is shown to influence the relative luminescence intensities of the donor bound excitons, enhancing the 3.361 eV peak, and changing the overall intensity of the PL spectrum. PL from He implanted ZnO is used to demonstrate that implantation damage is partially responsible for the variations observed in the PL of H implanted ZnO. IR spectra show that the increase in the relative intensity of the 3.361 eV peak coincides with an appearance of the H vibrational mode in the ZnO lattice. Our results indicate that the implanted H forms O–H bonds at Zn vacancies, and that it is these defect complexes which give rise to the shallow donors participating in the observed bound-exciton luminescence at 3.361 eV.
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Unidirectional beam emission from strained InGaAsP multiple-quantum-well quasistadium laser diodes

Takehiro Fukushima, Tomoko Tanaka, and Takahisa Harayama

Appl. Phys. Lett. 86, 171103 (2005); http://dx.doi.org/10.1063/1.1920430 (3 pages) | Cited 2 times

Online Publication Date: 19 April 2005

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We present unidirectional emission from strained InGaAsP multiple-quantum-well quasistadium laser diodes, whose resonators consist of two confocal end mirrors and two long, straight, sidewall mirrors. Far-field patterns exhibit highly directional emission at a 20° angle from the cavity axis. This angle corresponds to a unidirectional ring trajectory inside the resonator. We also report that the unidirectional emission can be explained by the phase locking of two resonator modes with different symmetry classes based on the extended Fox-Li mode calculation method.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.79.Bh Lenses, prisms and mirrors

An approach to the design of highly selective resonant-cavity-enhanced photodetectors

A. Ramam, G. K. Chowdhury, and S. J. Chua

Appl. Phys. Lett. 86, 171104 (2005); http://dx.doi.org/10.1063/1.1914964 (3 pages) | Cited 2 times

Online Publication Date: 19 April 2005

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The information capacity of a communication system employing a wavelength-division multiplexing scheme can be increased by reducing the free spectral range between different signals, reducing the full width at half maximum (FWHM), and detecting these closely spaced channels. After critically analyzing the design parameters of existing resonant-cavity-enhanced (RCE) p–i–n photodetectors, we have determined that more closely spaced channels can be detected either by increasing the length of a RCE p–i–n detector or by reducing the stop-band width of the bottom mirror. A masking procedure is described to determine the maximum cavity length attainable for any bottom distributed Bragg reflector (DBR) materials so that photodetector filters and detects only one wavelength, being insensitive to all other wavelengths. The optimized cavity length of single wavelength selective RCE detector operating at 1.3 μm using 42 ½ pairs of InAlGaAs/InP as a bottom DBR is 7.5 μm and its theoretical FWHM is 2.5 nm.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
42.15.Eq Optical system design
42.82.Bq Design and performance testing of integrated-optical systems
42.79.Bh Lenses, prisms and mirrors
42.79.Ci Filters, zone plates, and polarizers
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Self-stabilized and dispersion-compensated passively mode-locked Yb:Yttrium aluminum garnet laser

A. Agnesi, A. Guandalini, and G. Reali

Appl. Phys. Lett. 86, 171105 (2005); http://dx.doi.org/10.1063/1.1914965 (3 pages) | Cited 1 time

Online Publication Date: 19 April 2005

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Self-stabilized passive mode-locking of a diode-pumped Yb:yttrium aluminum garnet laser with a semiconductor saturable absorber was achieved using an off-phase-matching second-harmonic crystal. According to the numerical model, such a condition is accomplished by self-defocusing in the nonlinear crystal in the presence of positive intracavity dispersion. Robust mode locking with Fourier-limited 1.0-ps pulses was obtained, whereas mode locking, unassisted by the nonlinear crystal, yielded 2.2-ps pulses, with the laser operating near the edge of the stability region in order to minimize the saturation energy of the semiconductor device.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Fc Modulation, tuning, and mode locking
42.55.Xi Diode-pumped lasers
42.70.Hj Laser materials

Line-defect–waveguide laser integrated with a point defect in a two-dimensional photonic crystal slab

Atsushi Sugitatsu, Takashi Asano, and Susumu Noda

Appl. Phys. Lett. 86, 171106 (2005); http://dx.doi.org/10.1063/1.1920429 (3 pages) | Cited 10 times

Online Publication Date: 20 April 2005

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We realize an active two-dimensional (2D) photonic crystal laser with a combination of line defects and point defects. Based on a line-defect–waveguide laser in a 2D photonic crystal slab, we observe laser emission from the point defect at the waveguide mode-edge frequency when there is a frequency mismatch with the point-defect mode. This phenomenon is due to the wide-field distribution at the waveguide mode edge and its distortion by the adjacent point defect. Numerical calculations estimate the emission efficiency and are in good agreement with experimental results.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.70.Hj Laser materials
61.72.J- Point defects and defect clusters

Decomposition of KH2PO4 crystals during laser-induced breakdown

R. A. Negres, S. O. Kucheyev, P. DeMange, C. Bostedt, T. van Buuren, A. J. Nelson, and S. G. Demos

Appl. Phys. Lett. 86, 171107 (2005); http://dx.doi.org/10.1063/1.1921349 (3 pages) | Cited 10 times

Online Publication Date: 20 April 2005

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The structure of KH2PO4 single crystals (so-called KDP) irradiated with ∼ 3 ns, 355 nm laser pulses with fluences above the laser-induced breakdown threshold is studied by a combination of Raman scattering, photoluminescence, and soft x-ray absorption spectroscopies. We compare spectra from the as-grown material, surface and bulk laser-induced damage sites, as well as from KPO3 references. Results show that irradiation with fluences above the laser-induced breakdown threshold leads to decomposition of KDP at surface damage sites but not at bulk damage sites. New spectroscopic features are attributed to dehydration products. For the laser irradiation conditions used in this study, the decomposed near-surface layer absorbs photons at ∼ 3.4 eV (364 nm). These results may explain the recently reported fact that surface laser damage sites in KDP crystals tend to grow with subsequent exposure to high-power laser pulses, while bulk damage sites do not.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
61.66.Fn Inorganic compounds
79.20.Ds Laser-beam impact phenomena
78.30.Hv Other nonmetallic inorganics
78.70.Dm X-ray absorption spectra
78.55.Hx Other solid inorganic materials
42.70.Qs Photonic bandgap materials

Enhanced electrophosphorescence via highly efficient energy transfer from conjugated polymer

Tae-Ho Kim, Dong-Hee Yoo, Jong Hyeok Park, O Ok Park, Jae-Woong Yu, and Jai Kyeong Kim

Appl. Phys. Lett. 86, 171108 (2005); http://dx.doi.org/10.1063/1.1921356 (3 pages) | Cited 19 times

Online Publication Date: 20 April 2005

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We have demonstrated that efficient green electrophosphorescence is obtained via cascade energy transfer from poly(N-vinylcarbazole) (PVK) and host fluorescent polymer to the phosphorescent iridium complex. Efficient energy transfers from PVK to fluorescent polymer and then from this host polymer to iridium complex, fac-tris[2-(2-pyridinyl-kN)[5-(2,5-dimethylphenyl)phenyl]-kC]-iridium(III) [Ir(PDPP)3], were observed in the PVK/fluorescent polymer/Ir(PDPP)3 blend system, even though the chemical compatibility between this fluorescent polymer and Ir(PDPP)3 is very poor. The phase separation between the host polymer and Ir(PDPP)3 was restrained and highly efficient energy transfer also occurred by blending with PVK which has the good chemical compatibility with both host and guest materials. The resulting device (indium tin oxide/PEDOT/blend layer/BCP/Li:Al alloy) reaches a maximum external quantum efficiency of 8.9% and a luminous efficiency of 32 cd/A.
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78.60.-b Other luminescence and radiative recombination
64.75.-g Phase equilibria

Collective behavior and disorder-induced resonator of random lasers

Sheng Li, Zi-Jun Wang, Liang-Shan Chen, Xin Sun, and Thomas F. George

Appl. Phys. Lett. 86, 171109 (2005); http://dx.doi.org/10.1063/1.1920409 (3 pages) | Cited 2 times

Online Publication Date: 21 April 2005

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The localization caused by multiple scattering of lightwaves provides a mode for random laser action. It is shown that once the gain surpasses a certain threshold, photons are driven to localized modes, which greatly suppresses the energy loss and leads to laser emission. Concurrent with the localization of the random laser, unique collective behaviors of the localized modes appear, as distinguished from the other modes, which reveals the “invisible” microcavities of random lasers.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Rz Doped-insulator lasers and other solid state lasers

Terahertz gain in optically excited biased semiconductor superlattices

Aizhen Zhang, Dawei Wang, and M. M. Dignam

Appl. Phys. Lett. 86, 171110 (2005); http://dx.doi.org/10.1063/1.1922079 (3 pages) | Cited 5 times

Online Publication Date: 22 April 2005

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We investigate the terahertz-driven dynamics of excitons in an undoped optically excited biased semiconductor superlattice, including exciton-LO phonon scattering. We calculate the THz gain spectrum for a 820 fs THz pulse when the superlattice is excited by a 590 fs optical pulse. The gain arises because, in contrast to the single-electron case, the excitonic Wannier-Stark ladder is asymmetric with respect to absorption and emission. We find that gain coefficients greater than 100 cm−1 can be achieved at excitation densities for which domain formation should not occur.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
63.20.kk Phonon interactions with other quasiparticles
71.35.-y Excitons and related phenomena
78.70.Gq Microwave and radio-frequency interactions
78.45.+h Stimulated emission
73.21.Cd Superlattices
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