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23 Apr 2007

Volume 90, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 173502 (2007); http://dx.doi.org/10.1063/1.2732163 (3 pages)

Matthias Imboden, Pritiraj Mohanty, Alexei Gaidarzhy, Janet Rankin, and Brian W. Sheldon
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Cutoff wavelength of Hg1−xCdxTe epilayers by infrared photoreflectance spectroscopy

Jun Shao, Xiang Lü, Wei Lu, Fangyu Yue, Wei Huang, Ning Li, Jun Wu, Li He, and Junhao Chu

Appl. Phys. Lett. 90, 171101 (2007); http://dx.doi.org/10.1063/1.2731705 (3 pages) | Cited 7 times

Online Publication Date: 23 April 2007

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A comparative study of cutoff wavelength is performed by photocurrent (PC), transmission, and infrared photoreflectance (PR) spectroscopies on arsenic-doped Hg1−xCdxTe molecular beam epitaxial layers in the midinfrared spectral region. It is illustrated that (i) a shorter cutoff wavelength of PC response may be predicted by either the band gap or the energy of the half-maximum transmission and (ii) the main PR peak is coincident energetically to that of the third-derivative maximum of the PC spectrum. The mechanism behind is discussed with the aid of photoluminescence measurements. The results indicate that the infrared PR spectroscopy may serve as a contactless alternative to the PC spectroscopy for predicting the cutoff wavelength of narrow-gap HgCdTe epilayers reliably.
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78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Et II-VI semiconductors
73.61.Ga II-VI semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Raman intensity enhancement in silicon-on-insulator substrates by laser deflection at atomic force microscopy tips and particles

Carsten Georgi, Michael Hecker, and Ehrenfried Zschech

Appl. Phys. Lett. 90, 171102 (2007); http://dx.doi.org/10.1063/1.2730576 (3 pages) | Cited 11 times

Online Publication Date: 23 April 2007

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It is shown that Raman intensities of bulk and film in silicon-on-insulator substrates strongly depend on the incident angle of the exciting laser. In a backscattering geometry with perpendicular laser incidence, deflection at particles or atomic force microscopy tips can thereby lead to a selective enhancement of the film signal, which can be misinterpreted as surface/tip enhanced Raman scattering. The authors report strong enhancement effects by scattering at dielectric particles on silicon-on-insulator and silicon substrates as well as smaller effects for deflection at tips. In evaluating field enhancements on such substrates, this must be considered.
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78.30.Am Elemental semiconductors and insulators
68.37.Ps Atomic force microscopy (AFM)

Ultrafast transient photoinduced absorption in silicon nanocrystals: Coupling of oxygen-related states to quantized sublevels

Emmanouil Lioudakis, Andreas Othonos, and A. G. Nassiopoulou

Appl. Phys. Lett. 90, 171103 (2007); http://dx.doi.org/10.1063/1.2728756 (3 pages) | Cited 21 times

Online Publication Date: 24 April 2007

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The authors have studied transient photoinduced absorption in single monolayers of oxidized silicon nanocrystals. Transient photoinduced absorption measurements along with optical absorption and photoluminescence (PL) emission reveal that the light-absorption process takes place in defects related to strong PL emission, suggesting that the photoexcited carriers are in oxygen-related interface states. They have time-resolved ultrafast relaxation paths in oxygen-related states and quantized sublevels, which have important implications in the understanding of fundamental optical properties for this system.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
78.47.-p Spectroscopy of solid state dynamics

Multiple wavelength InGaAs quantum dot lasers using selective area epitaxy

S. Mokkapati, H. H. Tan, and C. Jagadish

Appl. Phys. Lett. 90, 171104 (2007); http://dx.doi.org/10.1063/1.2731729 (3 pages) | Cited 3 times

Online Publication Date: 24 April 2007

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The authors demonstrate multiple wavelength lasers fabricated from InGaAs quantum dots. Selective area epitaxy is used to grow the active region, consisting of five layer stack of InGaAs quantum dots with different band gap energies in selected regions of the substrate, for fabrication of the lasers. The mechanism responsible for engineering of the band gap of quantum dots is discussed. The performance of the selectively grown lasers is compared to the lasers fabricated from structures grown in a standard, nonselective area growth process.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Enhanced spontaneous emission at 1.55 μm from colloidal PbSe quantum dots in a Si photonic crystal microcavity

Z. Wu, Z. Mi, P. Bhattacharya, T. Zhu, and J. Xu

Appl. Phys. Lett. 90, 171105 (2007); http://dx.doi.org/10.1063/1.2731657 (3 pages) | Cited 33 times

Online Publication Date: 24 April 2007

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The authors report on the design, fabrication, and characterization of 1.55 μm Si-based photonic crystal microcavity light emitters utilizing PbSe quantum dots. Efficient coupling of emission from PbSe quantum dots to Si photonic crystal membrane microcavity is achieved by inserting the quantum dots in a central air hole in the microcavity. Enhancement of spontaneous emission with linewidth of ∼ 2.0 nm is observed at 1550 nm at room temperature. The Purcell factor and the spontaneous emission coupling factor are estimated to be 35 and 0.04, respectively.
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78.67.Hc Quantum dots
78.66.Hf II-VI semiconductors
42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design

Nonlinear mode mixing in dual-wavelength semiconductor lasers with tunnel junctions

S. M. Nekorkin, A. A. Biryukov, P. B. Demina, N. N. Semenov, B. N. Zvonkov, V. Ya. Aleshkin, A. A. Dubinov, V. I. Gavrilenko, K. V. Maremyanin, S. V. Morozov, A. A. Belyanin, V. V. Kocharovsky, and Vl. V. Kocharovsky

Appl. Phys. Lett. 90, 171106 (2007); http://dx.doi.org/10.1063/1.2731523 (3 pages) | Cited 4 times

Online Publication Date: 25 April 2007

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The authors demonstrate and study two- and three-wavelength generations in the semiconductor diode laser with a tunnel junction separating two different quantum-well active regions integrated within a single waveguide. To avoid resonant cross absorption of the modes at different frequencies and achieve phase matching, the laser waveguide is designed to generate the first-order transverse mode at a longer wavelength and the third-order mode at a shorter wavelength. Excellent agreement with the designed and measured device parameters is observed. Intracavity nonlinear mixing leading to sum-frequency and second-harmonic generation is demonstrated.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Distributed Bragg reflector laser using buried SiO2 grating and self-aligned band gap tuning

J. H. Teng, J. R. Dong, S. J. Chua, B. S. Foo, M. Y. Lai, Y. J. Wang, S. S. Ang, and R. Yin

Appl. Phys. Lett. 90, 171107 (2007); http://dx.doi.org/10.1063/1.2733601 (3 pages) | Cited 3 times

Online Publication Date: 25 April 2007

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The authors report a technology to make a distributed Bragg reflector laser with buried dielectric grating and band gap tuned reflector region. The Bragg reflector is constructed by high coupling coefficient gratings made of SiO2 and InP. The band gap of the reflector is blueshifted by self-aligned quantum well intermixing using the buried SiO2 grating itself. The photoluminescence peak wavelength can be shifted by ∼ 45 meV for the quantum well sample covered by SiO2 grating compared to thermal shift only at annealing temperature of 800 °C for 100 s. The enhanced interdiffusion is caused by the P vacancies generated at SiO2 and InP interfaces as proved by secondary ion mass spectroscopy.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Plasmonic effects and visible light diffraction in three-dimensional opal-metal photonic crystals

A. V. Akimov, A. A. Meluchev, D. A. Kurdyukov, A. V. Scherbakov, A. Holst, and V. G. Golubev

Appl. Phys. Lett. 90, 171108 (2007); http://dx.doi.org/10.1063/1.2724894 (3 pages) | Cited 7 times

Online Publication Date: 25 April 2007

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The angular dependence of the reflectivity spectrum for visible light was measured in opal-metal (Ag and W) composites with a high filling factor. The diffraction patterns were observed at a wavelength essentially exceeding the period of a three-dimensional photonic structure. The authors offer a qualitative explanation based on the similarity between the experimental observations and those modified by the three-dimensional periodicity plasmonic effects in two-dimensional periodic structures with a subwavelength defect.
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42.70.Qs Photonic bandgap materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Terahertz continuous-wave large-area traveling-wave photomixers on high-energy low-dose ion-implanted GaAs

E. A. Michael, I. Cámara Mayorga, R. Güsten, A. Dewald, and R. Schieder

Appl. Phys. Lett. 90, 171109 (2007); http://dx.doi.org/10.1063/1.2722235 (3 pages) | Cited 4 times

Online Publication Date: 25 April 2007

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Nitrogen ion implantation at 3 MeV and low doses into commercial semi-insulating GaAs (107 Ω cm) is used to manufacture continuously operated metal-semiconductor-metal terahertz photomixer radiation sources based on a traveling-wave interdigitated-finger coplanar stripline structure. The authors systematically investigated the terahertz efficiency over the implantation dose range of 5.6×1011–1.8×1013 ions/cm2 and determined the optimum implantation dose range for operation in the frequency range 500–1000 GHz, where a significant higher efficiency is obtained compared to low-temperature-grown GaAs.
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84.40.Az Waveguides, transmission lines, striplines
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals

Single-frequency active Q-switched distributed fiber laser using acoustic waves

Martina Delgado-Pinar, Antonio Díez, José Luis Cruz, and Miguel V. Andrés

Appl. Phys. Lett. 90, 171110 (2007); http://dx.doi.org/10.1063/1.2732832 (3 pages) | Cited 9 times

Online Publication Date: 26 April 2007

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This letter presents a single mode, actively Q-switched distributed feedback fiber laser. Acoustic pulses are launched into an erbium-doped fiber Bragg grating, resulting in the introduction of a traveling defect. Thus, a transmission peak appears in the reflection band while the pulse travels along the grating. This effect allows the laser to operate in a Q-switched regime, providing optical pulses which repetition rate was continuously tuned up to 10 kHz. Pulses of 168 mW of peak power and 73 ns of temporal width were obtained at low repetition rate.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

 Tunable few-optical-cycle pulses with passive carrier-envelope phase stabilization from an optical parametric amplifier

C. Manzoni, D. Polli, G. Cirmi, D. Brida, S. De Silvestri, and G. Cerullo

Appl. Phys. Lett. 90, 171111 (2007); http://dx.doi.org/10.1063/1.2732834 (3 pages) | Cited 9 times

Online Publication Date: 26 April 2007

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The authors report on a scheme for the generation of few-optical-cycle pulses broadly tunable in the visible with passively stabilized carrier-envelope phase (CEP). The system starts with an infrared optical parametric amplifier in which both pump and seed are derived from an amplified, non-CEP-stabilized Ti:sapphire laser. The passively stabilized idler beam is then spectrally broadened through white-light generation and seeds a blue-pumped noncollinear optical parametric amplifier. The system produces few-optical-cycle pulses tunable from 500 to 800 nm, with energy up to 5 μJ and 0.23 rad rms CEP fluctuations.
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42.65.Yj Optical parametric oscillators and amplifiers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Back side thermal imaging of integrated circuits at high spatial resolution

G. Tessier, M. Bardoux, C. Boué, C. Filloy, and D. Fournier

Appl. Phys. Lett. 90, 171112 (2007); http://dx.doi.org/10.1063/1.2732179 (3 pages) | Cited 10 times

Online Publication Date: 26 April 2007

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In integrated circuits, most of the heating is produced in the active layers below the surface, making thermal measurements extremely difficult. The authors demonstrate that near infrared thermoreflectance can provide thermal imaging inside the circuit, through its silicon substrate. The use of an InGaAs camera with a noncoherent illumination in the 1.1–1.7 μm band allows fast thermal imaging with a diffraction-limited resolution of 1.7 μm. A silicon solid immersion lens was then used to further improve the resolution to 440 nm, corresponding to an effective numerical aperture of 2.36.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
42.79.Pw Imaging detectors and sensors

Gradual degradation of red-emitting high-power diode laser bars

Mathias Ziegler, Tran Quoc Tien, Sandy Schwirzke-Schaaf, Jens W. Tomm, Bernd Sumpf, Götz Erbert, Myriam Oudart, and Julien Nagle

Appl. Phys. Lett. 90, 171113 (2007); http://dx.doi.org/10.1063/1.2732202 (3 pages) | Cited 3 times

Online Publication Date: 26 April 2007

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The authors analyze early stages of gradual degradation in highly reliable 650 nm emitting high-power diode laser arrays with continuous wave emission powers of 2.5 W (facet load of 4 mW/μm). In all cases the edges of the metallized emitter stripes are identified as the starting points of gradual degradation. The magnitude of the observed degradation signatures, however, is highly correlated with the bar-specific packaging-induced strain at each emitter. We find a bar-specific effect, namely, the presence of packaging-induced strain, to be the driving force of gradual degradation. Our findings point to the significance of proper strain management in advanced device structures.
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42.55.Px Semiconductor lasers; laser diodes

Manipulation of tunneling frequencies using magnetic fields for resonant tunneling effects of surface plasmons

Yung-Chiang Lan, Yun-Chorng Chang, and Peng-Hsiao Lee

Appl. Phys. Lett. 90, 171114 (2007); http://dx.doi.org/10.1063/1.2732827 (3 pages) | Cited 19 times

Online Publication Date: 26 April 2007

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This work investigates the manipulation of terahertz surface plasmons (SPs) on a semiconductor surface by applying an external static magnetic field. The dispersion relations of the coupled surface magnetoplasmon under the Voigt configuration in the semiconductor-insulator-semiconductor structure are derived. For a TM-polarized wave that is normally incident onto a semiconductor film with periodic narrow grooves on both surfaces, the applied external static magnetic field with the Voigt configuration redshifts the frequencies of the SP-induced resonant tunneling. This phenomenon is attributable to the reduction in the effective plasma frequency by the applied magnetic field.
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73.40.Ty Semiconductor-insulator-semiconductor structures
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
78.66.-w Optical properties of specific thin films
78.20.Ls Magneto-optical effects

Butt-end fiber coupling to a surface-emitting Γ-point photonic crystal band edge laser

Yeonsang Park, Sunghwan Kim, Chaeyoung Moon, Heonsu Jeon, and Hyo Jin Kim

Appl. Phys. Lett. 90, 171115 (2007); http://dx.doi.org/10.1063/1.2732835 (3 pages) | Cited 7 times

Online Publication Date: 26 April 2007

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The authors demonstrate a compact and efficient fiber coupling scheme for a surface-emitting photonic crystal laser by using a cleaved fiber tip connected to a wavelength-division-multiplexing 1×2 fiber coupler. Simultaneous optical excitation and laser light collection are achieved for a 1.55 μm InGaAsP graphite-lattice Γ-point band edge laser. On comparing with the conventional microphotoluminescence setup based on an objective lens, their direct butt coupling setup is much simpler and yet offers the fiber-coupled output approximately ten times higher. Finite-difference time-domain simulations confirm that the Γ-point band edge laser exhibits the desired vertical emission property and that the fiber coupling efficiency can be as high as 30%.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.81.Qb Fiber waveguides, couplers, and arrays

Electro-optically tunable second-harmonic-generation gratings in ion-exfoliated thin films of periodically poled lithium niobate

Djordje Djukic, Guiem Cerda-Pons, Ryan M. Roth, Richard M. Osgood, Jr., Sasha Bakhru, and Hassaram Bakhru

Appl. Phys. Lett. 90, 171116 (2007); http://dx.doi.org/10.1063/1.2728739 (3 pages) | Cited 8 times

Online Publication Date: 27 April 2007

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The authors demonstrate that thin, single-crystal films fabricated by ion exfoliation of a bulk periodically poled LiNbO3 (PPLN) crystal reduced the tuning voltages for electro-optically tunable harmonic generation in PPLN devices. The tuning voltage of ±150 V resulted in 0.5 nm total tuning of the second harmonic signal in the authors’ 10-μm-thick device, compared to an order of magnitude higher tuning voltage value needed in a comparable bulk device.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.-a Optical materials
42.79.Wc Optical coatings
42.79.Dj Gratings
78.66.Nk Insulators
78.20.Jq Electro-optical effects

Phonon polariton generation and detection using near-field heterodyne transient grating method

Kenji Katayama, Qing Shen, Taro Toyoda, and Keith A. Nelson

Appl. Phys. Lett. 90, 171117 (2007); http://dx.doi.org/10.1063/1.2734388 (3 pages) | Cited 3 times

Online Publication Date: 27 April 2007

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A technique for the generation and detection of phonon polariton was developed based on the near-field heterodyne transient grating method. It features a compact and simple optical setup and easy wavelength tuning ability of the phonon polariton. The wavelength was tuned by changing the grating spacing of a transmission grating positioned in front of a sample, and this was performed by sliding a glass plate with transmission gratings with many different grating spacings along the glass plate surface.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.79.Dj Gratings

Ambipolar light-emitting organic field-effect transistors using a wide-band-gap blue-emitting small molecule

Tomo Sakanoue, Masayuki Yahiro, Chihaya Adachi, Hiroyuki Uchiuzou, Takayoshi Takahashi, and Akio Toshimitsu

Appl. Phys. Lett. 90, 171118 (2007); http://dx.doi.org/10.1063/1.2734389 (3 pages) | Cited 22 times

Online Publication Date: 27 April 2007

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The authors applied a wide-band-gap (2.9 eV) molecule of 4,-4′-bis(styryl)biphenyl (BSBP) as an active layer in light-emitting organic field-effect transistors. They found that BSBP provided both relatively high field-effect hole mobility of 0.01 cm2/V s and photoluminescence efficiency of 20% in thin film. They achieved ambipolar operation by without breaking vacuum through devices’ preparation and measurements, applying aluminum contacts, and inserting a hydroxyl-free poly(methylmethacrylate) layer, and light emission was observed when the device was operated in the ambipolar mode. The results presented here will open the way to fabricating efficient light-emitting transistors with high mobility.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices

Direct observation of trapped carriers in polydiacetylene films by optical second harmonic generation

Takaaki Manaka, Hideki Kohn, Yuki Ohshima, Eunju Lim, and Mitsumasa Iwamoto

Appl. Phys. Lett. 90, 171119 (2007); http://dx.doi.org/10.1063/1.2734469 (3 pages) | Cited 8 times

Online Publication Date: 27 April 2007

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Trapped carriers in polydiacetylene (PDA) films were directly observed by the electric field induced second harmonic generation (EFISHG) using field effect transistor (FET) structure. Response of EFISHG signal from PDA-FET with applying voltage depended strongly on the polarity of gate voltage. For negative bias, which promotes hole injection from source electrode, EFISHG signal was not observed during bias application, whereas it was enhanced after turning off the bias. Electric field formed by trapped holes in PDA activated the EFISHG signal for the negative bias condition.
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73.61.Ph Polymers; organic compounds
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.66.Qn Polymers; organic compounds

Laser frequency offset locking using electromagnetically induced transparency

S. C. Bell, D. M. Heywood, J. D. White, J. D. Close, and R. E. Scholten

Appl. Phys. Lett. 90, 171120 (2007); http://dx.doi.org/10.1063/1.2734471 (3 pages) | Cited 12 times

Online Publication Date: 27 April 2007

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The authors have used an electromagnetically induced transparency resonance in rubidium as a dispersive reference to lock the relative frequency of two lasers to the atomic ground-state hyperfine splitting. The beat frequency between the two lasers directly generates a microwave signal at 3.036 GHz (85Rb) or 6.835 GHz (87Rb). High bandwidth (600 kHz) feedback was achieved with only low-frequency (10 MHz) electronics using the frequency modulation sideband method. The spectral width of the microwave beat frequency was reduced to less than 1 kHz. The technique offers a convenient and low-cost method suitable for many topical two-frequency experiments, including coherent population trapping, slow light, lasing without inversion, and Raman sideband cooling.
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42.60.Fc Modulation, tuning, and mode locking
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Generation of 10 μJ ultrashort terahertz pulses by optical rectification

K.-L. Yeh, M. C. Hoffmann, J. Hebling, and Keith A. Nelson

Appl. Phys. Lett. 90, 171121 (2007); http://dx.doi.org/10.1063/1.2734374 (3 pages) | Cited 109 times

Online Publication Date: 27 April 2007

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Generation of near single-cycle pulses centered at 0.5 THz frequency with up to 10 μJ energy, 100 μW average power, and 5.0 MW peak power was demonstrated by tilting the intensity front of a femtosecond optical pump pulse from a 10 Hz Ti:sapphire laser to match the phonon-polariton phase velocity to the group velocity of the pump pulses in a lithium niobate crystal. Terahertz pulse intensity as high as 10 MW/cm2 was achieved. The photon conversion efficiency was 45% and the calculated peak electric field strength at the focus of an off-axis parabolic mirror was 250 kV/cm.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Low threshold current single-cell hexapole mode photonic crystal laser

Min-Kyo Seo, Kwang-Yong Jeong, Jin-Kyu Yang, Yong-Hee Lee, Hong-Gyu Park, and Sung-Bock Kim

Appl. Phys. Lett. 90, 171122 (2007); http://dx.doi.org/10.1063/1.2734391 (3 pages) | Cited 16 times

Online Publication Date: 27 April 2007

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The authors report an electrically driven, hexapole mode, single-cell photonic crystal laser operating at 1537.8 nm. Electrical current is supplied through a submicrometer-sized current post beneath the cavity center. This wavelength-scale single-cell photonic crystal laser operates in a single mode with threshold current of ∼ 100 μA at room temperature. Operation in the hexapole mode is confirmed by the near-field profile, far-field polarization, and the finite-difference time-domain computation based on the fabricated cavity structure.
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42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.70.Hj Laser materials
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Time- and locally resolved photoluminescence of semipolar GaInN/GaN facet light emitting diodes

Thomas Wunderer, Peter Brückner, Joachim Hertkorn, Ferdinand Scholz, Gareth J. Beirne, Michael Jetter, Peter Michler, Martin Feneberg, and Klaus Thonke

Appl. Phys. Lett. 90, 171123 (2007); http://dx.doi.org/10.1063/1.2734498 (3 pages) | Cited 13 times

Online Publication Date: 27 April 2007

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The authors investigate the carrier lifetime and photoluminescence (PL) intensity of a semipolar GaInN/GaN sample which was realized by growing five GaInN/GaN quantum wells on the {1math01} side facets of selectively grown n-GaN stripes that have a triangular shape running along the 〈11math0〉 direction. Time- and locally resolved PL measurements show drastically reduced lifetimes for the semipolar sample of only 650 ps at 4 K whereas lifetimes exceeding 50 ns were found for a polar reference sample. Furthermore, more than a doubling of the luminescence intensity and a significantly reduced blueshift of the PL peak wavelength with increasing excitation power density provide further evidence for the presence of reduced piezoelectric fields in the semipolar sample.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Low-noise optical injection locking of a resonant tunneling diode to a stable optical frequency comb

T. M. Ramond, L. Hollberg, P. W. Juodawlkis, and S. D. Calawa

Appl. Phys. Lett. 90, 171124 (2007); http://dx.doi.org/10.1063/1.2734368 (3 pages) | Cited 3 times

Online Publication Date: 27 April 2007

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Optical injection locking of a resonant tunneling diode (RTD) oscillator has been demonstrated using ultrashort pulses from a mode-locked Ti:sapphire laser operating at a 1 GHz pulse rate. The source of the optical signal is a mode-locked femtosecond laser whose optical frequency comb is phase locked to a H-maser stabilized frequency synthesizer. An exceptionally large capture range of more than 5 MHz is observed. The system produces stable microwave signals with low phase noise, which at 1 GHz is less than −74 dBc/Hz for a 10 Hz offset. The noise of the microwave injection-locked RTD signal matches that of the input optical pulses.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
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High current permanent discharges in air induced by femtosecond laser filamentation

A. Houard, C. D’Amico, Y. Liu, Y. B. Andre, M. Franco, B. Prade, A. Mysyrowicz, E. Salmon, P. Pierlot, and L.-M. Cleon

Appl. Phys. Lett. 90, 171501 (2007); http://dx.doi.org/10.1063/1.2734396 (3 pages) | Cited 15 times

Online Publication Date: 27 April 2007

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Filaments created in air by an intense femtosecond laser pulse in the presence of an electric field generate a highly conductive permanent plasma column.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.80.-s Electric discharges
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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