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25 Feb 2008

Volume 92, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 92, 081101 (2008); http://dx.doi.org/10.1063/1.2883874 (3 pages)

Marcel W. Pruessner, Todd H. Stievater, and William S. Rabinovich
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In-plane microelectromechanical resonator with integrated Fabry–Pérot cavity

Marcel W. Pruessner, Todd H. Stievater, and William S. Rabinovich

Appl. Phys. Lett. 92, 081101 (2008); http://dx.doi.org/10.1063/1.2883874 (3 pages) | Cited 12 times

Online Publication Date: 25 February 2008

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A silicon-on-insulator in-plane microelectromechanical resonator coupled to a high-Q (Q ≈ 4,200), high finesse (FMax = 265) optical Fabry–Pérot microcavity is presented. The cavity utilizes high reflectance dry-etched silicon/air distributed Bragg reflectors. By suspending one of the Bragg mirrors to a microbridge resonator, the mirror can be displaced and the cavity is tuned. Using electrostatic actuation, bidirectional cavity tuning from −12.1 to +17.0 nm (29.1 nm total range) is demonstrated near 1601 nm wavelength. The device also enables measurement of thermal-mechanical noise with sensitivity better than 10 fm/Hz1/2 and may find application in high resolution sensors.
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07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.82.Et Waveguides, couplers, and arrays
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Bh Lenses, prisms and mirrors
42.79.Ci Filters, zone plates, and polarizers

Temperature dependence of the gain profile for terahertz quantum cascade lasers

Rikard Nelander and Andreas Wacker

Appl. Phys. Lett. 92, 081102 (2008); http://dx.doi.org/10.1063/1.2884686 (3 pages) | Cited 30 times

Online Publication Date: 25 February 2008

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We study the rapid decrease of peak gain in resonant-phonon terahertz quantum cascade lasers with increasing temperature. The effect of various microscopic scattering processes on the gain profile as a function of temperature is discussed. We argue that increased broadening, primarily due to increased impurity scattering, and not diminishing population inversion, is the main reason for the reduction of peak gain.
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42.55.Px Semiconductor lasers; laser diodes
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Near-infrared waveguide-based nickel silicide Schottky-barrier photodetector for optical communications

Shiyang Zhu, M. B. Yu, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 92, 081103 (2008); http://dx.doi.org/10.1063/1.2885089 (3 pages) | Cited 20 times

Online Publication Date: 25 February 2008

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Integrated silicon-on-insulator waveguide-based silicide Schottky-barrier photodetectors were fabricated using low-cost standard Si complementary metal-oxide-semiconductor processing technology. The thin epitaxial NiSi2 layer formed by solid-state Ti-interlayer mediated epitaxy on the top of Si-waveguide absorbs light propagating through the waveguide effectively and exhibits excellent rectifying property on both p-Si and n-Si. NiSi2/p-Si detectors with tapered geometry demonstrate dark current of ∼ 3.0 nA at room temperature, responsivity of ∼ 4.6 mA/W at wavelengths ranging from 1520 to 1620 nm, and 3 dB bandwidth of ∼ 2.0 GHz. The approaches for further improvement in responsivity are addressed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
85.30.Tv Field effect devices

Eu2+–Mn2+ phosphor saturation in 5 mm light emitting diode lamps

A. A. Setlur, J. J. Shiang, and U. Happek

Appl. Phys. Lett. 92, 081104 (2008); http://dx.doi.org/10.1063/1.2885093 (3 pages) | Cited 27 times

Online Publication Date: 25 February 2008

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This letter reports on phosphor quenching by saturation, a sublinear phosphor response with excitation intensity, in light emitting diode (LED) packages using 405 nm LEDs and Ca5(PO4)3Cl:Eu2+,Mn2+ phosphors. This saturation is due to the high light flux incident on the phosphors in these LED packages and the slow radiative relaxation rate of Mn2+. Apart from known saturation processes of Mn2+ ground state depletion and energy transfer between excited Mn2+ ions, an additional quenching pathway, Eu2+→Mn2+ (excited) energy transfer, is taken into account to quantitatively fit both the efficiency under pulsed operation and the time-resolved luminescence of Ca5(PO4)3Cl:Eu2+,Mn2+.
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85.60.Jb Light-emitting devices

Raman gain from waveguides inscribed in KGd(WO4)2 by high repetition rate femtosecond laser

S. M. Eaton, C. A. Merchant, R. Iyer, A. J. Zilkie, A. S. Helmy, J. S. Aitchison, P. R. Herman, D. Kraemer, R. J. D. Miller, C. Hnatovsky, and R. S. Taylor

Appl. Phys. Lett. 92, 081105 (2008); http://dx.doi.org/10.1063/1.2884188 (3 pages) | Cited 14 times

Online Publication Date: 26 February 2008

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We report the formation of waveguides in Raman-active KGd(WO4)2 with a focused, high repetition rate femtosecond laser. Parallel guiding regions, formed to either side of the laser-induced damage track, supported TE and TM modes that coupled efficiently to optical fiber at telecom wavelengths. Micro-Raman spectroscopy of the guiding regions revealed the preservation of the characteristic 768 and 901 cm−1 Raman mode intensities. Raman gain with 6% efficiency was demonstrated for the 768 cm−1 Raman line by pumping the waveguide with an infrared 80 ps source, the first time Raman gain has been reported in laser formed waveguides.
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42.62.-b Laser applications
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques

Investigation of Pr3+ as a sensitizer in quantum-cutting fluoride phosphors

Te-Ju Lee, Li-Yang Luo, Bing-Ming Cheng, Wei-Guang Diau, and Teng-Ming Chen

Appl. Phys. Lett. 92, 081106 (2008); http://dx.doi.org/10.1063/1.2884690 (3 pages) | Cited 13 times

Online Publication Date: 26 February 2008

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A quantum-cutting (QC) phosphor K2GdF5:Eu3+ shows poor optical absorption and a theoretical quantum efficiency (QE) of 107% in the ultraviolet (UV) and vacuum ultraviolet (VUV) excitation spectral ranges. Pr3+ was codoped as a sensitizer in K2GdF5:Eu3+, thus increasing the absorption in the UV and VUV spectral regions; the theoretical QE of K2GdF5:Eu3+,Pr3+ was increased to 138%. The spectra indicate that the possible mechanisms of QC and energy transfer differ from those of phosphors containing the Gd3+–Eu3+ couple. Temporally resolved measurements of fluorescence decay confirm the proposed QC mechanism for the phosphor containing the Gd3+–Eu3+,Pr3+ system.
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78.55.Hx Other solid inorganic materials
78.40.Ha Other nonmetallic inorganics

Monolithic InGaN-based white light-emitting diodes with blue, green, and amber emissions

Sung-Nam Lee, H. S. Paek, H. Kim, T. Jang, and Y. Park

Appl. Phys. Lett. 92, 081107 (2008); http://dx.doi.org/10.1063/1.2887884 (3 pages) | Cited 4 times

Online Publication Date: 27 February 2008

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We demonstrated a monolithic white light-emitting diodes (LEDs) epitaxial structure with blue, green, and amber emissions by introducing the blue InGaN/GaN five quantum wells (QWs) and InGaN/GaN single quantum well (SQW) with In-phase separated green/amber emissions as an active layer. Three wavelength emissions were developed by increasing the thickness of InGaN SQW grown on blue InGaN five QWs. From high resolution transmission electron microscope, In-phase separation was clearly observed in a 3.5-nm-thick InGaN SQW. In-phase separation would be generated by the spinodal decomposition which was promoted by the composition pulling effect related to the increment of well thickness. Therefore, white lighting LEDs with three wavelengths for blue emission from InGaN/GaN five QWs and green/amber emissions were achieved by the In-phase separation in InGaN SQW.
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85.60.Jb Light-emitting devices

Near-field optical trapping with an ultrashort pulsed laser beam

Smitha Kuriakose, Dru Morrish, Xiaosong Gan, James W. M. Chon, Kishan Dholakia, and Min Gu

Appl. Phys. Lett. 92, 081108 (2008); http://dx.doi.org/10.1063/1.2888771 (3 pages) | Cited 5 times

Online Publication Date: 28 February 2008

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We report the focused evanescent optical trapping of nonfluorescent and fluorescent dielectric microspheres using a femtosecond laser. The experiment confirms that the trapping efficiency increases with the size of the particles. As a result, a pulsed laser has been used to trap particles in the Mie regime and to excite whispering gallery modes in them. The excitation of whispering gallery modes in a near-field femtosecond trap shows a significant suppression of the two-photon fluorescence background with an improvement of the photon storage factor by 46%, as compared to far-field two-photon excitation.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift

Terahertz wave generation from a dc-biased multimode laser

Sylwester Latkowski, Frederic Surre, and Pascal Landais

Appl. Phys. Lett. 92, 081109 (2008); http://dx.doi.org/10.1063/1.2884525 (3 pages) | Cited 4 times

Online Publication Date: 28 February 2008

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We present results achieved in the generation of terahertz wave by a semiconductor laser. It is a Fabry–Pérot based device with shallow grooves implemented on its p-side to engineer the longitudinal mode spectrum. The laser is dc-biased and temperature controlled at 298 K. The main two modes are separated by 3 nm at 1550 nm with a side-mode-suppression ratio of 25 dB. Using a frequency resolved optical gating, evidence of mode beating at 373 GHz is observed. With a bolometer interfaced to a Fourier transform interferometer, the second harmonic signal is measured at 690 GHz.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Dispersive gain and loss in midinfrared quantum cascade laser

D. G. Revin, M. R. Soulby, J. W. Cockburn, Q. Yang, C. Manz, and J. Wagner

Appl. Phys. Lett. 92, 081110 (2008); http://dx.doi.org/10.1063/1.2884699 (3 pages) | Cited 11 times

Online Publication Date: 28 February 2008

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We report the measurements of dispersive gain (simultaneous coexistence of gain and losses on a single intersubband transition) in a quantum cascade laser. Broadband transmission spectra through the waveguide of a λ ∼ 4.7 μm In0.53Ga0.47As/AlAs0.56Sb0.44/InP quantum cascade laser have been studied at a bias below laser threshold and at different temperatures. For a certain range of current, and at temperatures higher than about 150 K, the transmission spectra show clear dispersive gain/loss behavior with the possibility for intersubband gain to be observed even without global population inversion between laser levels.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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