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2 Apr 2012

Volume 100, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 100, 144101 (2012); http://dx.doi.org/10.1063/1.3697983 (4 pages)

H. Xu (徐涵), Wei Yu (余玮), M. Y. Yu (郁明阳), A. Y. Wong (黄燿煇), Z. M. Sheng (盛政明), M. Murakami (村上匡且), and J. Zhang (张杰)
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Tunable clover-shaped GaN photonic bandgap structures patterned by dual-step nanosphere lithography

K. H. Li, Zetao Ma, and H. W. Choi

Appl. Phys. Lett. 100, 141101 (2012); http://dx.doi.org/10.1063/1.3698392 (5 pages) | Cited 2 times

Online Publication Date: 2 April 2012

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The fabrication of close-packed clover-shaped photonic crystal structure on GaN by dual-step nanosphere lithography is demonstrated. By shrinkage of spheres prior to pattern transfer, a non-closed-packed clover-shaped photonic bandgap (PBG) structure, as designed by modified 3D finite-difference time-domain simulation, is also realized. The PBG of the close-packed and non-close-packed clover-shaped structures is verified through optical transmission spectroscopy, found to agree well with simulated results. A threefold enhancement in photoluminescence (PL) intensity is observed from the optimized structure, when the PBG is tuned to overlap with the emission band of the InGaN/GaN multi-quantum wells. From time-resolved PL measurements, shortened decay lifetimes are observed.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
78.47.je Time resolved light scattering spectroscopy
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Optical generation of polarized photoluminescence from GaAs(100)

Zhan Hu, Sima Singha, Daniel H. Rich, and Robert J. Gordon

Appl. Phys. Lett. 100, 141102 (2012); http://dx.doi.org/10.1063/1.3698469 (4 pages) | Cited 2 times

Online Publication Date: 2 April 2012

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Polarized photoluminescence from GaAs(100) was generated using shaped ultrashort laser pulses. A train of three pulses separated by an integer multiple of the longitudinal optical phonon period produced p-polarized continuum emission, whereas trains with half-integer multiples of the phonon period as well as single Gaussian pulses produced s-polarized emission. The p-polarized emission is attributed to recombination of carriers in the L-valley, resulting from plasma generation and coherent phonon-excitation by the pulse train, whereas the s-polarized emission is caused by reflection by the melted surface of unpolarized plasma emission.
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78.55.Cr III-V semiconductors
63.20.dd Measurements
78.47.jd Time resolved luminescence

Phase sensitive monitoring of electron bunch form and arrival time in superconducting linear accelerators

C. Kaya, C. Schneider, A. Al-Shemmary, W. Seidel, M. Kuntzsch, J. Bhattacharyya, M. Mittendorff, P. Evtushenko, S. Winnerl, G. Staats, M. Helm, N. Stojanovic, P. Michel, and M. Gensch

Appl. Phys. Lett. 100, 141103 (2012); http://dx.doi.org/10.1063/1.3699025 (3 pages) | Cited 1 time

Online Publication Date: 2 April 2012

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In this Letter, we present a simple approach for monitoring electron bunch form and arrival time combining electro-optic sampling and phase and frequency sensitive signal detection. The sensitivity of the technique has the potential to allow online diagnostics to be performed down to bunch charges in the femto coulomb regime. The concept has high impact for the developments of the next generation of 4th generation x-ray light sources working with long pulse trains or continuous wave mode of operation.
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29.20.Ej Linear accelerators

Transmission and temperature sensing characteristics of a selectively liquid-filled photonic-bandgap-fiber-based Sagnac interferometer

Xibao Zheng, Yan-ge Liu, Zhi Wang, Tingting Han, Chengli Wei, and Jinjie Chen

Appl. Phys. Lett. 100, 141104 (2012); http://dx.doi.org/10.1063/1.3699026 (4 pages) | Cited 2 times

Online Publication Date: 2 April 2012

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A selectively liquid-filled photonic-bandgap-fiber-based Sagnac interferometer is proposed and demonstrated. Extraordinary transmission and sensing characteristics of the interferometer are observed and investigated theoretically and experimentally. Due to the unique modal and group birefringence characteristics of the material-infiltrated photonic bandgap fiber, the temperature sensitivity of the interference peaks strongly depends on the wavelength. Furthermore, the interference peaks at the two edges of the bandgap appear to shift in the opposite direction alongside changes in the temperature, providing a method of achieving two- or multi-parameter simultaneous sensing measurement with a compact structure.
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42.81.Pa Sensors, gyros
07.20.Dt Thermometers
07.60.Ly Interferometers
07.60.Vg Fiber-optic instruments
42.70.Qs Photonic bandgap materials
42.81.Dp Propagation, scattering, and losses; solitons

Lens-less edge-pumped high power microchip laser

Weipeng Kong and Takunori Taira

Appl. Phys. Lett. 100, 141105 (2012); http://dx.doi.org/10.1063/1.3699225 (4 pages) | Cited 1 time

Online Publication Date: 2 April 2012

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We report the demonstration of compact lens-less microchip laser, which is directly pumped by single-emitter diode chips from multiple directions. The lens-less design makes the microchip laser more compact; the multi-direction designable pump schemes can realize a Gaussian shape. As a preliminary result, continuous wave output power of 32.5 W and slope efficiency of 45% was obtained by 9-direction pumped Yb:YAG ceramic microchip. Further, 27.2 W single peak Gaussian beam was obtained by a small adjustment of the output mirror. Power scalability is easy by increasing the number of diodes to 27 to achieve 100-watt-level microchip laser.
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42.55.Sa Microcavity and microdisk lasers

Advantages of GaN based light-emitting diodes with a p-InGaN hole reservoir layer

Taiping Lu, Shuti Li, Chao Liu, Kang Zhang, Yiqin Xu, Jinhui Tong, Lejuan Wu, Hailong Wang, Xiaodong Yang, Yian Yin, Guowei Xiao, and Yugang Zhou

Appl. Phys. Lett. 100, 141106 (2012); http://dx.doi.org/10.1063/1.3700722 (3 pages) | Cited 7 times

Online Publication Date: 3 April 2012

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A p-type InGaN hole reservoir layer (HRL) was designed and incorporated in GaN based light-emitting diodes (LEDs) to enhance hole injection efficiency and alleviate efficiency droop. The fabricated LEDs with p-type HRL exhibited higher light output power, smaller emission energy shift and broadening as compared to its counterpart. Based on electrical and optical characteristics analysis and numerical simulation, these improvements are mainly attributed to the alleviated band bending in the last couple of quantum well and electron blocking layer, and thus better hole injection efficiency. Meanwhile, the efficiency droop can be effectively mitigated when the p-InGaN HRL was used.
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85.60.Jb Light-emitting devices
02.60.-x Numerical approximation and analysis

Bistability in silicon microring resonator based on strain induced by a piezoelectric lead zirconate titanate thin film

Y. Sebbag, I. Goykhman, B. Desiatov, T. Nachmias, O. Yoshaei, M. Kabla, S. E. Meltzer, and U. Levy

Appl. Phys. Lett. 100, 141107 (2012); http://dx.doi.org/10.1063/1.3701587 (4 pages)

Online Publication Date: 3 April 2012

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We demonstrate bistability in a submicron silicon optical phase shifter based on the photoelastic effect. The strain magnitude is electrically controlled by a piezoelectric thin film placed on top of the device. The hysteresis behavior of the piezoelectric response shows potential application as bistable device independent of the optical intensity.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.-e Optical elements, devices, and systems
77.65.-j Piezoelectricity and electromechanical effects
77.55.H- Piezoelectric and electrostrictive films
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

The effect of viewing angle on the spectral behavior of a Gd plasma source near 6.7 nm

Colm O’Gorman, Takamitsu Otsuka, Noboru Yugami, Weihua Jiang, Akira Endo, Bowen Li, Thomas Cummins, Padraig Dunne, Emma Sokell, Gerry O’Sullivan, and Takeshi Higashiguchi

Appl. Phys. Lett. 100, 141108 (2012); http://dx.doi.org/10.1063/1.3701593 (4 pages) | Cited 1 time

Online Publication Date: 5 April 2012

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We have demonstrated the effect of viewing angle on the extreme ultraviolet (EUV) emission spectra of gadolinium (Gd) near 6.7 nm. The spectra are shown to have a strong dependence on viewing angle when produced with a laser pulse duration of 10 ns, which may be attributed to absorption by low ion stages of Gd and an angular variation in the ion distribution. Absorption effects are less pronounced at a 150-ps pulse duration due to reduced opacity resulting from plasma expansion. Thus for evaluating source intensity, it is necessary to allow for variation with both viewing angle and target orientation.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Dg Plasma sources
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Fi Transport properties

Ultrafast excited state dynamics and dispersion studies of nonlinear optical properties in dinaphthoporphycenes

Debasis Swain, P. T. Anusha, T. Shuvan Prashant, Surya P. Tewari, Tridib Sarma, Pradeepta K. Panda, and S. Venugopal Rao

Appl. Phys. Lett. 100, 141109 (2012); http://dx.doi.org/10.1063/1.3701274 (5 pages) | Cited 5 times

Online Publication Date: 6 April 2012

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Ultrafast excited state dynamics of dinaphthoporphycenes were investigated using femtosecond and picosecond degenerate pump-probe techniques at 600 nm and 800 nm, respectively. Femtosecond pump-probe data indicated photo-induced absorption at 600 nm resulting from two-photon/single photon excitation, whereas picosecond pump-probe data demonstrated photo-bleaching which was a consequence of three-photon absorption. The fastest lifetimes (100–120 fs) observed are attributed to the intramolecular vibrational relaxation, the slower ones (1–3 ps) to internal conversion, and the slowest components (7–10 ps) to non-radiative decay back to ground state. Z-scan studies in the 560–600 nm range were also carried out.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)
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