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30 Jul 2007

Volume 91, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 052901 (2007); http://dx.doi.org/10.1063/1.2767146 (3 pages)

Wei-Feng Rao and Yu U. Wang
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Simultaneous optical trapping of microparticles in multiple planes by a modified self-imaging effect on a chip

Y. Y. Sun, J. Bu, L. S. Ong, and X.-C. Yuan

Appl. Phys. Lett. 91, 051101 (2007); http://dx.doi.org/10.1063/1.2767148 (3 pages) | Cited 9 times

Online Publication Date: 30 July 2007

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The authors propose a three-dimensional (3D) optical trapping of microparticles in multiple planes simultaneously based on a modified self-imaging effect. Similar to the Talbot self-imaging effect, the modified self-imaging effect is induced by a layer of trapped particles and it is subsequently used as a periodic grating structure to generate its own self-imaging pattern in 3D. Based on this secondary layer-by-layer self-imaging effect, optical trapping of silica and polystyrene colloidal particles at different planes in a microchamber are demonstrated experimentally.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
07.60.Ly Interferometers
42.79.Dj Gratings
82.70.Dd Colloids

GaInNAs double-barrier quantum well infrared photodetector with the photodetection at 1.24 μm

B. S. Ma, W. J. Fan, Y. X. Dang, W. K. Cheah, W. K. Loke, W. Liu, D. S. Li, S. F. Yoon, D. H. Zhang, H. Wang, and C. H. Tung

Appl. Phys. Lett. 91, 051102 (2007); http://dx.doi.org/10.1063/1.2767185 (3 pages) | Cited 7 times

Online Publication Date: 30 July 2007

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A GaInNAs/AlAs/AlGaAs double-barrier quantum well infrared photodetector was grown by molecular beam epitaxy and fabricated by standard device processes. The growth structure of the as-grown sample was verified by x-ray diffraction measurement. The photoluminescence emission peak, which is related to the interband transition in the GaInNAs well, was observed at ∼ 1.2 eV. After annealing at 650 °C, a large blueshift of 40 meV was observed. The photocurrent peak at 1.24 μm is associated with the intersubband transitions in the conduction band of the GaInNAs quantum well. The ten-band k∙p calculations agree with the above observations.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.De Semiconductor-device characterization, design, and modeling
81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells

Generation of high-quality optical vortex beams in free-space propagation by microfabricated wedge with spatial filtering technique

X.-C. Yuan, B. P. S. Ahluwalia, H. L. Chen, J. Bu, J. Lin, R. E. Burge, X. Peng, and H. B. Niu

Appl. Phys. Lett. 91, 051103 (2007); http://dx.doi.org/10.1063/1.2760183 (3 pages) | Cited 2 times

Online Publication Date: 30 July 2007

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The authors propose a low-pass 2f spatial filter for improving optical vortex beams in terms of circular geometry generated by a microfabricated wedge in free space. Compared with a conventional wedge, they are able to realize high-quality vortex beams with Q value close to 1 in free-space propagation. Physical mechanism behind the technique is found that it removes the diffraction artifacts as well as higher spatial frequency components of the quasivortex beams based on a wedge and hence the filtered beam is reconstructed with minimized distortions.
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41.85.Ct Particle beam shaping, beam splitting
41.85.Ew Particle beam profile, beam intensity
42.79.Ci Filters, zone plates, and polarizers

Deep subsurface waveguides with circular cross section produced by femtosecond laser writing

V. Diez-Blanco, J. Siegel, A. Ferrer, A. Ruiz de la Cruz, and J. Solis

Appl. Phys. Lett. 91, 051104 (2007); http://dx.doi.org/10.1063/1.2761298 (3 pages) | Cited 14 times

Online Publication Date: 31 July 2007

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A combination of low numerical aperture focusing optics, in order to minimize spherical aberration, and beam shaping with a slit has been used to produce waveguides in fused silica by femtosecond laser writing. Waveguides with circular cross section and low losses are produced over a large depth window (>7 mm) without changing any experimental parameter. Diffraction induces beam divergence along the axis perpendicular to the slit, leading to a shift of the focal plane. The focal intensity distribution can be predicted by a hybrid model combining Gaussian beam propagation with imaging of the slit into the material.
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42.62.Cf Industrial applications
42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques

Ultraviolet electro-optic amplitude modulation in β-BaB2O4 waveguides

R. Degl’Innocenti, A. Majkic, P. Vorburger, G. Poberaj, P. Günter, and M. Döbeli

Appl. Phys. Lett. 91, 051105 (2007); http://dx.doi.org/10.1063/1.2761484 (3 pages) | Cited 2 times

Online Publication Date: 31 July 2007

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The authors report on the realization of an electro-optical amplitude modulator based on β-BaB2O4 (BBO) waveguide operating in the ultraviolet wavelength range down to 257 nm. The ridge waveguides are produced by He+ implantation, photolithography masking, and plasma etching. Electrodes are deposited by the standard lift-off technique. A minimum half-wave voltage times modulator length Vπ×1 of 43 V cm has been demonstrated at 257 nm in a 6.5-mm-long modulator. Because of BBO’s broad transparency range (190–3500 nm), such device could be employed in the deep ultraviolet with Vπ×1 estimated to reach 24 V cm at 200 nm.
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42.79.Gn Optical waveguides and couplers
42.79.Hp Optical processors, correlators, and modulators

AlN air-bridge photonic crystal nanocavities demonstrating high quality factor

M. Arita, S. Ishida, S. Kako, S. Iwamoto, and Y. Arakawa

Appl. Phys. Lett. 91, 051106 (2007); http://dx.doi.org/10.1063/1.2757596 (3 pages) | Cited 21 times

Online Publication Date: 31 July 2007

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The authors report an achievement of high quality AlN ultraviolet photonic crystal nanocavities. Convex AlN air-bridge structures with embedded GaN quantum dots have been formed by utilizing photoelectrochemical etching of 6H-SiC substrates. Room-temperature microscopic photoluminescence measurements reveal the high quality of the nanocavities. For the lowest-order cavity mode of a 150-nm-period nanocavity with seven missing holes, the highest Q factor (>2400) ever reported in nitride-based photonic crystals has been obtained.
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42.70.Qs Photonic bandgap materials
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

All-optical format conversion using a periodically poled lithium niobate waveguide and a reflective semiconductor optical amplifier

Jian Wang, Junqiang Sun, Qizhen Sun, Dalin Wang, Minjuan Zhou, Xinliang Zhang, Dexiu Huang, and M. M. Fejer

Appl. Phys. Lett. 91, 051107 (2007); http://dx.doi.org/10.1063/1.2761513 (3 pages) | Cited 11 times

Online Publication Date: 31 July 2007

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In the present letter, the authors report on the realization of all-optical format conversion by using the cascaded sum- and difference-frequency generation in a periodically poled lithium niobate waveguide and the active mode locking in a reflective-semiconductor-optical-amplifier-based fiber ring laser. Tunable format conversions from nonreturn-to-zero pseudorandom binary sequence (PRBS) signal to return-to-zero PRBS idler at 10 and 20 Gbit/s are observed in the experiment.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Wd Fiber lasers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Photocurrent analysis of a fast Ge p-i-n detector on Si

M. Oehme, J. Werner, E. Kasper, S. Klinger, and M. Berroth

Appl. Phys. Lett. 91, 051108 (2007); http://dx.doi.org/10.1063/1.2757599 (3 pages) | Cited 12 times

Online Publication Date: 31 July 2007

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Germanium vertical p-i-n photodetectors grown on silicon with molecular beam epitaxy are investigated. The photocurrent of a high speed detector structure is analyzed at infrared wavelengths of around 1.3 μm. The dark current and photocurrent were measured for reverse and forward biased detectors. It is clearly shown that the photocurrent is proportional to the width of the depletion layer. This means that the fast carriers from the depletion layer generate mainly the photocurrent and by this the high speed operation of the germanium detector is explained. Nearly abrupt junctions and low background doping allow zero bias operation of these detectors.
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85.60.Dw Photodiodes; phototransistors; photoresistors
72.40.+w Photoconduction and photovoltaic effects

Nanoimprinted circular grating distributed feedback dye laser

Yan Chen, Zhenyu Li, Zhaoyu Zhang, Demetri Psaltis, and Axel Scherer

Appl. Phys. Lett. 91, 051109 (2007); http://dx.doi.org/10.1063/1.2757600 (3 pages) | Cited 19 times

Online Publication Date: 31 July 2007

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The authors demonstrate an optically pumped surface emitting polymer dye laser fabricated by nanoimprint lithography. The laser is based on an organic dye hosted within a poly(methylmethacrylate) matrix coated on a transparent substrate, and the laser cavity consists of a second order circular grating distributed feedback structure. The authors achieved lasing at 618 nm with 0.18 nm linewidth and 1.31 μJ/mm2 pump threshold. The nanoimprinted solid-state dye laser offers a low-cost coherent light source for laboratory-on-chip spectroscopy systems. The laser also has a low pump threshold and a geometry well matched to light-emitting diode pump sources, which provide an interesting alternative for constructing portable polymer laser devices.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems

Object localization with 10 nm accuracy by x-ray phase contrast projection imaging

C. Ollinger, C. Fuhse, S. Kalbfleisch, R. Tucoulou, and T. Salditt

Appl. Phys. Lett. 91, 051110 (2007); http://dx.doi.org/10.1063/1.2757601 (3 pages) | Cited 2 times

Online Publication Date: 31 July 2007

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The present work focuses on the question of localizing single object by hard x-ray phase contrast projection imaging. The authors present a setup where an x-ray channel waveguide defines a “quasi-point source” used to illuminate and image an object in a highly coherent cone beam. Knife edge fluorescence scans revealed a beam diameter of 75 nm at a distance of 30 μm behind the guide. The recorded image corresponds to an in-line hologram of the object which can be reconstructed numerically. Object translations and associated shifts in the hologram allow for the 10 nm localization accuracy.
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42.40.-i Holography
41.50.+h X-ray beams and x-ray optics
42.82.Et Waveguides, couplers, and arrays

Single-step fabrication of Fresnel microlens array on sapphire substrate of flip-chip gallium nitride light emitting diode by focused ion beam

Ming-Kwei Lee and Kwei-Kuan Kuo

Appl. Phys. Lett. 91, 051111 (2007); http://dx.doi.org/10.1063/1.2757602 (3 pages) | Cited 8 times

Online Publication Date: 31 July 2007

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A simple one-step focused ion beam milling technique was used to fabricate a Fresnel microlens array on the backside of sapphire substrate of a gallium nitride blue light emitting diode. The optical output power from the flip-chip gallium nitride blue light emitting diode is enhanced to about 1.68 times at the injection current of 20 mA. The spatial light distribution from the backside of flip-chip gallium nitride blue light emitting diode with a Fresnel microlens array shows a uniform and stronger light emission.
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85.60.Jb Light-emitting devices
42.79.Bh Lenses, prisms and mirrors
42.86.+b Optical workshop techniques

GaN ultraviolet photosensors capped by low-temperature aluminium nitride layer

P. C. Chang

Appl. Phys. Lett. 91, 051112 (2007); http://dx.doi.org/10.1063/1.2757606 (3 pages) | Cited 2 times

Online Publication Date: 31 July 2007

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GaN UV sensors with an in situ grown 30 nm thick low-temperature aluminium nitride (LT-AlN) cap layer were fabricated. Scanning probe microscopy showed that surface pits of threading dislocations were almost invisible when the GaN active layer was capped with a LT-AlN layer. The dark leakage current of these sensors was comparably much smaller than that of conventional sensors without the LT-AlN cap layer, owing to a thicker and higher potential barrier of the LT-AlN cap layer and effective surface passivation. With −1 V applied bias, it was found that the UV-to-visible rejection ratio was 3.42×103 for the sensor with the LT-AlN cap layer. In brief, incorporating a LT-AlN cap layer into the sensors can beneficially suppress the dark leakage current and improve the UV-to-visible rejection ratio.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.-e Optical elements, devices, and systems
42.79.Pw Imaging detectors and sensors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.65.Rv Passivation

Observation of femtojoule optical bistability involving Fano resonances in high-Q/Vm silicon photonic crystal nanocavities

Xiaodong Yang, Chad Husko, Chee Wei Wong, Mingbin Yu, and Dim-Lee Kwong

Appl. Phys. Lett. 91, 051113 (2007); http://dx.doi.org/10.1063/1.2757607 (3 pages) | Cited 30 times

Online Publication Date: 31 July 2007

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The authors observe experimentally optical bistability enhanced through Fano interferences in high-Q localized silicon photonic crystal resonances (Q ∼ 30 000 and modal volume ∼ 0.98 cubic wavelengths). This phenomenon is analyzed through nonlinear coupled-mode formalism, including the interplay of χ(3) effects such as two-photon absorption and related free-carrier dynamics, and optical Kerr as well as thermal effects and linear losses. Experimental and theoretical results demonstrate Fano resonance based bistable states with switching thresholds of 185 μW and 4.5 fJ internally stored cavity energy ( ∼ 540 fJ consumed energy) in silicon for scalable optical buffering and logic.
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42.65.An Optical susceptibility, hyperpolarizability
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Qs Photonic bandgap materials
42.82.Et Waveguides, couplers, and arrays

Comparing Monte Carlo simulation and pseudospectral time-domain numerical solutions of Maxwell’s equations of light scattering by a macroscopic random medium

Snow H. Tseng and Boyeh Huang

Appl. Phys. Lett. 91, 051114 (2007); http://dx.doi.org/10.1063/1.2767777 (3 pages) | Cited 9 times

Online Publication Date: 1 August 2007

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The Monte Carlo simulation of light scattering by a cluster of dielectric spheres is compared with numerical solutions of Maxwell’s equations via the pseudospectral time-domain technique. By calculating the total scattering cross-section (TSCS) spectrum, respectively, the spectral light scattering characteristics are determined. Since the Monte Carlo simulation falls short to accurately account for coherent interference effects, it is shown that the Monte Carlo simulation yields TSCS spectra that significantly deviate from the numerical solutions of Maxwell’s equations. Therefore, it is necessary to resort to Maxwell’s equations in order to accurately determine the light scattering characteristics of a macroscopic geometry.
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42.25.Fx Diffraction and scattering
42.25.Dd Wave propagation in random media
41.20.-q Applied classical electromagnetism

Temperature-dependent photoresponsivity and high-temperature (190 K) operation of a quantum dot infrared photodetector

Xuejun Lu, Jarrod Vaillancourt, and Mark J. Meisner

Appl. Phys. Lett. 91, 051115 (2007); http://dx.doi.org/10.1063/1.2766655 (3 pages) | Cited 26 times

Online Publication Date: 1 August 2007

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In this letter, a longwave infrared (LWIR) InAs–InGaAs quantum dot infrared photodetector with a peak detection wavelength of 9.9 μm is reported. A large photoresponsivity of 2.5 A/W and a high peak specific photodetectivity D* of 1.1×108 cm Hz1/2/W were obtained at the operating temperature of 190 K. The QDIP showed a strong temperature-dependent photoresponsivity over the temperature range from 78 to 190 K. This effect is shown to be attributable to temperature-dependent electron capture probability.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Heteroepitaxy of AlGaN on bulk AlN substrates for deep ultraviolet light emitting diodes

Z. Ren, Q. Sun, S.-Y. Kwon, J. Han, K. Davitt, Y. K. Song, A. V. Nurmikko, H.-K. Cho, W. Liu, J. A. Smart, and L. J. Schowalter

Appl. Phys. Lett. 91, 051116 (2007); http://dx.doi.org/10.1063/1.2766841 (3 pages) | Cited 21 times

Online Publication Date: 1 August 2007

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The authors report the growth of AlGaN epilayers and deep ultraviolet (UV) light emitting diodes (LEDs) on bulk AlN substrates. Heteroepitaxial nucleation and strain relaxation are studied through controlled growth interruptions. Due to a low density of preexisting dislocations in bulk AlN, the compressive strain during AlGaN heteroepitaxy cannot be relieved effectively. The built-up of strain energy eventually induces either an elastic surface roughening or plastic deformation via generation and inclination of dislocations, depending on the stressor interlayers and growth parameters used. AlGaN LEDs on bulk AlN exhibit noticeable improvements in performance over those on sapphire, pointing to a promising substrate platform for III-nitride UV optoelectronics.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Polarization of light emission by 460 nm GaInN/GaN light-emitting diodes grown on (0001) oriented sapphire substrates

Martin F. Schubert, Sameer Chhajed, Jong Kyu Kim, E. Fred Schubert, and Jaehee Cho

Appl. Phys. Lett. 91, 051117 (2007); http://dx.doi.org/10.1063/1.2757594 (3 pages) | Cited 20 times

Online Publication Date: 1 August 2007

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Measurements on the polarization of top- and side-emitted light as a function of direction are performed for 460 nm GaInN unpackaged and packaged light-emitting diode (LED) chips with a multiquantum well (MQW) GaInN/GaN active region grown on (0001) oriented sapphire substrates. Side emission is found to be highly polarized with the electric field in the plane of the MQW. Intensity ratios for in-plane to normal-to-plane polarization reach values as high as 7:1, while the total intensity for the in-plane polarization is more than twice as large compared to the normal-to-plane polarization. Despite these measured polarization characteristics, conventional packaged LEDs are found to be virtually unpolarized due to packaging.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence

Observation of Kastler ring stimulated emission from an organic microcavity

P. Schneeweiss, M. Sudzius, R. Gehlhaar, M. Hoffmann, V. G. Lyssenko, H. Fröb, and K. Leo

Appl. Phys. Lett. 91, 051118 (2007); http://dx.doi.org/10.1063/1.2767216 (3 pages)

Online Publication Date: 1 August 2007

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The authors report the observation of an intense conical emission from an organic microcavity. The emission is characterized experimentally and modeled as a higher order Fabry-Perot mode predicted 45 years ago by Kastler [Appl. Opt. 1, 17 (1962)] . A distinct cone is only visible above the normal mode laser threshold which implies a stimulated emission nature of the off-axial light. The input/output characteristics of normal and cone emissions hint that both originate from one and the same lasing mode.
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42.55.Sa Microcavity and microdisk lasers
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems

Phonon-assisted stimulated emission from pendeoepitaxy GaN stripes grown on 6H-SiC substrates

Y. C. Chang, Y.-L. Li, D. B. Thomson, and R. F. Davis

Appl. Phys. Lett. 91, 051119 (2007); http://dx.doi.org/10.1063/1.2767239 (3 pages) | Cited 3 times

Online Publication Date: 2 August 2007

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Phonon-assisted stimulated emission has been demonstrated by photopumping GaN stripes grown via pendeoepitaxy on 6H-SiC (0001) substrates. Transverse-electric-polarized emission with well-defined Fabry-Pérot modes located at one longitudinal optical phonon energy (90 meV) below the band gap of GaN was observed at 77 K. An effective refractive index of 8.578 was obtained using a cavity length of 13.3 μm and a mode spacing of 0.6 nm. This value is significantly higher than the value previously reported in the literature using ellipsometry, which indicates that the absorption loss is more severe during lasing when the excess carrier concentration is very high.
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78.45.+h Stimulated emission
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Silicon nanocrystal-based photosensor on low-temperature polycrystalline-silicon panels

Wen-Jen Chiang, Chih-Yang Chen, Chrong-Jung Lin, Ya-Chin King, An-Thung Cho, Chia-Tian Peng, Chih-Wei Chao, Kun-Chih Lin, and Feng-Yuan Gan

Appl. Phys. Lett. 91, 051120 (2007); http://dx.doi.org/10.1063/1.2767241 (3 pages) | Cited 4 times

Online Publication Date: 2 August 2007

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A photodetector, comprising a layer of silicon nanocrystals that is sandwiched between two electrodes, is proposed and demonstrated in a photosensing application on low-temperature polysilicon panels. Laser annealing of silicon-rich oxide films can form nanocrystals that respond optimally to a certain absorption spectrum of a light source. These silicon nanocrystals are smaller than 10 nm in diameter, which size determines the effectiveness of their quantum confinement, and promote electron-hole pair generation in the photosensing region because of their direct band gap. Besides obtaining a photosensitivity that is comparable to that of a p‐i‐n diode, which is currently used in low-temperature polysilicon technology, the sensor maximizes the photosensing area of a pixel by its stacked structure.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Reduced injection current induced blueshift in an InGaN/GaN quantum-well light-emitting diode of prestrained growth

Chi-Feng Huang, Cheng-Yen Chen, Chih-Feng Lu, and C. C. Yang

Appl. Phys. Lett. 91, 051121 (2007); http://dx.doi.org/10.1063/1.2767243 (3 pages) | Cited 12 times

Online Publication Date: 2 August 2007

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The authors demonstrate the smaller blueshift in increasing injection current level of an InGaN/GaN quantum-well (QW) light-emitting diode (LED) of a longer electroluminescence (EL) peak wavelength based on the prestrained growth technique when compared with the result of a LED of a shorter EL peak wavelength based on the conventional growth technique. The smaller blueshift can be attributed to more contribution to light emission from the deeper QWs of higher indium contents when the injection current level is increased in the prestrain sample. It can also be attributed to the stronger carrier localization because of the stronger composition clustering in the prestrain sample of higher indium contents. Carrier localization can reduce the influences of the quantum-confined Stark effect and its screening process.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Buckling behaviors of single-walled carbon nanotubes filled with metal atoms

L. Wang, H. W. Zhang, Z. Q. Zhang, Y. G. Zheng, and J. B. Wang

Appl. Phys. Lett. 91, 051122 (2007); http://dx.doi.org/10.1063/1.2767249 (3 pages) | Cited 13 times

Online Publication Date: 2 August 2007

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Molecular dynamics method is employed to investigate the buckling deformations of single-walled carbon nanotubes (SWCNTs) filled with nickel (Ni), copper (Cu), and platinum (Pt) atoms under axial compression. The critical buckling strains of filled tubes decrease linearly before a critical number of metal atoms and then increase linearly when more atoms are encapsulated. For SWCNT completely filled with metals, its critical strain is larger than that of the hollow tube. Furthermore, the critical strain of SWCNT completely filled with Ni atoms is larger than that of the tube fully filled with Cu or Pt atoms.
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62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.05.ub Fullerenes and related materials

Improved performance of In0.6Ga0.4As/AlAs0.67Sb0.33/InP quantum cascade lasers by introduction of AlAs barriers in the active regions

D. G. Revin, J. W. Cockburn, M. J. Steer, R. J. Airey, M. Hopkinson, A. B. Krysa, L. R. Wilson, and S. Menzel

Appl. Phys. Lett. 91, 051123 (2007); http://dx.doi.org/10.1063/1.2767767 (3 pages) | Cited 7 times

Online Publication Date: 2 August 2007

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The authors demonstrate that the performance of strain compensated InP-based InGaAs/AlAsSb quantum cascade lasers (QCLs) can be improved if AlAsSb barriers in the laser active regions are replaced by AlAs layers. The introduction of AlAs is intended to help suppress compositional fluctuations due to interdiffusion at the quantum well/barrier interfaces. An In0.6Ga0.4As/AlAs0.67Sb0.33 QCL with AlAs barriers displays pulsed laser operation at wavelength of 4.1 μm, for temperatures up to at least 320 K, with lower threshold current density and higher output optical power than the reference laser with identical design but with AlAs0.67Sb0.33 barriers throughout the entire core region.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Silicon based organic semiconductor laser

A. E. Vasdekis, S. A. Moore, A. Ruseckas, T. F. Krauss, I. D. W. Samuel, and G. A. Turnbull

Appl. Phys. Lett. 91, 051124 (2007); http://dx.doi.org/10.1063/1.2764553 (3 pages) | Cited 10 times

Online Publication Date: 2 August 2007

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The authors demonstrate silicon based visible lasers as potential optical interconnects by combining silicon processed resonators and solution processed light-emitting polymers. The high refractive index and absorption coefficient of silicon at these wavelengths were addressed by developing distributed Bragg reflector resonators on a silicon-on-insulator substrate. The performance of the hybrid structure was characterized and analyzed in comparison to an all-silica counterpart and mechanisms for controlling the number of longitudinal modes and for tuning the emission wavelength were explored.
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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

Single-component reflecting objective for low-temperature spectroscopy in the entire visible region

Satoru Fujiyoshi, Masanori Fujiwara, Changman Kim, Michio Matsushita, Antoine M. van Oijen, and Jan Schmidt

Appl. Phys. Lett. 91, 051125 (2007); http://dx.doi.org/10.1063/1.2767778 (3 pages) | Cited 4 times

Online Publication Date: 2 August 2007

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A single-component reflecting objective was constructed for low-temperature spectroscopy with optimal imaging and transmission properties at all visible wavelengths. The performance of the objective immersed in superfluid helium at a temperature of 1.5 K was tested by comparing dark-field images of uncolored polymer beads taken at wavelengths of 400 and 800 nm. Under conditions optimized for imaging at both wavelengths, the size of the image is <1.3 times of the diffraction limit. The objective collects emission from a point source at focus with a solid angle of 0.32π sr.
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07.60.Rd Visible and ultraviolet spectrometers
42.79.Bh Lenses, prisms and mirrors
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