Volume 93, Issue 9, 01 September 2008
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- organic electronics and photonics
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
Three-dimensional-confined structures with triangular-lattice air-hole photonic crystal patterns were fabricated to enhance the light output from silicon rich oxide/multilayer stack. The intensity and profile of spontaneous emission were found to be efficiently modulated by controlling the optical modes of the periodic arrays via varying their structural parameters. With lattice constant/radius of , the photoluminescence intensity was found to be enhanced by nearly nine times in the vertical direction. The mechanisms for different enhancement features have been theoretically analyzed based on coherent scattering and quantum electrodynamic effects, well supporting the experimental observation.
- LASERS, OPTICS, AND OPTOELECTRONICS
93(2008); http://dx.doi.org/10.1063/1.2976551View Description Hide Description
Self-assembled InSbsubmonolayerquantum dots(QDs) in an InAs matrix have been grown by molecular beam epitaxy using and fluxes. The structures exhibit bright midinfrared photoluminescence up to room temperature. Intense room temperature electroluminescence with a peak at wavelength near was observed from light emitting diode structures containing ten InSbsubmonolayerQD sheets inserted within the InAs active region.
Mercury Bromide : A promising nonlinear optical material in IR region with a high laser damage threshold93(2008); http://dx.doi.org/10.1063/1.2969059View Description Hide Description
Nonlinear optical (NLO) crystals have played a key role in laser technology, and the existing materials for the IR range showed relatively low laser damage threshold in common. A NLO material is presented here. It shows a powdersecond harmonic generation about ten times as large as that of , a wide transparency in whole mid-IR region (from 2.5 to ), and a good stability to the environment. Most importantly it exhibits a high laser damage threshold of about . Therefore, it is believed that is a promising candidate for NLO materials in the IR region.
93(2008); http://dx.doi.org/10.1063/1.2977873View Description Hide Description
A structure of symmetrical metal-cladding waveguide, which contains optically nonlinear material in the guiding layer, is proposed to control the lateral shift of the reflected beam via an external electric field. Owing to the high sensitivity of ultrahigh-order modes, any minute index change of the waveguide will lead to a dramatic variation of the resonance condition, which gives rise to a change of the lateral beam displacement. Experimental result shows that the electric control of the lateral beam shift is realized in a range of .
93(2008); http://dx.doi.org/10.1063/1.2977994View Description Hide Description
The impact of the interface roughness on intersubband transitions (ISTs) in quantum wells is analyzed as an inhomogeneous broadening due to localization rather than a traditional scattering process. The results offer simple explanation for the temperature dependent spectra of gain and absorption in quantum cascade lasers and also for the strong IST polariton phenomena.
93(2008); http://dx.doi.org/10.1063/1.2970046View Description Hide Description
In this work, we study the interaction of ultrashort midinfrared pulses with the active medium of an quantum cascade laser emitting at an wavelength. Applying an electro-optic sampling technique allowed us to measure the complete phase resolved transmission spectra at operating conditions below and above lasing threshold in a spectral range much broader than the gain band width. Far below threshold, we locate broadband resonant absorption, which spectrally overlaps with the electrically induced gain, forming areas of net absorption and net gain. Above threshold, gain clamping is seen, and it is found that echoes delayed by the round trip time experience spectral pulse shaping converging toward the emission spectrum.
93(2008); http://dx.doi.org/10.1063/1.2978096View Description Hide Description
We report on a terahertz emitter made out of black silicon. The black surface structure absorbs the whole optical pump power in the very surface. In contrast to expectations for indirect semiconductors, the black structure shows an emission in the terahertz range. The emitted radiation of the black silicon crystal is characterized for different parameters using terahertz time-domain spectroscopy.
93(2008); http://dx.doi.org/10.1063/1.2973988View Description Hide Description
We report on the improved performance of quantum-well waveguide solar cells via light scattering from deposited dielectric or metal nanoparticles. The integration of metal or dielectric nanoparticles above the quantum-well solar celldevice is shown to couple normally incident light into lateral optical propagation paths, with optical confinement provided by the refractive index contrast between the quantum-well layers and surrounding material. With minimal optimization, short-circuit current density increases of 12.9% and 7.3% and power conversion efficiency increases of 17% and 1% are observed for silica and Aunanoparticles, respectively.
93(2008); http://dx.doi.org/10.1063/1.2976664View Description Hide Description
Compact high power broadband superfluorescent fiber source has been demonstrated using an ultrashort -codoped phosphate glass fiber. The fiber is 10.4-cm-long and at 1.68 W pump power, an output power of 16.85 mW, a mean wavelength of 1540.9 nm, a bandwidth of 18.4 nm, and a slope efficiency of 18.6% have been obtained. The dependence of output power, mean wavelength, and bandwidth stability on pump power and fiber length are also studied, and there is an excellent agreement between the theoretical results and experimental data.
93(2008); http://dx.doi.org/10.1063/1.2965113View Description Hide Description
InGaN optical confinement layers (OCLs) were introduced into blue-violet AlInGaN-based laser diodes(LDs), resulting in the drastic improvements of lasing performance. Comparing with conventional LD structure, the lowest threshold current density of has been achieved by adding -thick InGaN OCLs which represented maximum optical confinement factor. Additionally, we observed the high quantum efficiency and the uniform emission intensity distribution of InGaN quantum wells grown on lower InGaN OCL than on typical GaN layer. Upper InGaN OCL can reduce Mgdiffusion from -type layers to InGaN active region by separating the distance between InGaN quantum wells and -type layers.
93(2008); http://dx.doi.org/10.1063/1.2976162View Description Hide Description
A large-area terahertz emitter based on an interdigital finger electrode photoconductive switch on low-temperature grownGaAs attached to a hexagonal microlens array is demonstrated. The hexagonal arranged microlenses direct the incident IR excitation pulses into specified electrode gaps, resulting in constructive interference in the terahertz far field. Using a Ti:sapphire oscillator running at with pulses, average power at optical excitation is obtained. The maximum IR-to-terahertz conversion efficiency achieved is .
93(2008); http://dx.doi.org/10.1063/1.2977998View Description Hide Description
We report on light-induced optical tuning of colloidal photonic crystalsdoped with goldnanoparticles (Au-nps). By resonantly exciting the Au-np surface plasmon absorption with picosecond pulses at in a standard pump-probe setup, we observed permanent changes in the stop band resonance around , with blue wavelength shifts as large as and associated to a nanoparticle reshaping. Fine tuning was achieved by controlling either the pulse energy or the irradiation time.
Anisotropic optical gain in -plane multiple quantum well laser diode wafers fabricated on the low defect density freestanding GaN substrates93(2008); http://dx.doi.org/10.1063/1.2978242View Description Hide Description
The threshold power density for the stimulated emission (SE) at 400 nm of -plane multiple quantum well(QW)laser diode(LD) wafer excited with a stripe along the -axis was found to be lower than along the -axis, although the SEs exhibited transverse electric field mode for both configurations. The result was explained according to the polarization selection rules for the lowest and the second lowest energy interband transitions in anisotropically strained -plane InGaN QWs. In case of the LD wafer lased at 426 nm, SE was observed only along the -axis, where pronounced broadening of the gain spectrum was found. Because the equivalent internal quantum efficiency was only 44%, further reductions in nonradiative defect density and the width of gain spectrum are essential to realize longer wavelength LDs.
Quantitative differential interference contrast microscopy based on structured-aperture interference93(2008); http://dx.doi.org/10.1063/1.2977870View Description Hide Description
We report a quantitative differential interference contrast (DIC) microscope based on a structured-aperture (SA) wavefront sensor. Unlike a conventional DIC microscope, the SA-DIC microscope can separate the amplitude and the phase gradient information of the image wavefront, and form quantitative intensity and DIC images of the sample with good resolution; our prototype achieved resolution . Furthermore, due to the nonpolarization nature of the microscope, we were able to image birefringent samples without artifacts.
93(2008); http://dx.doi.org/10.1063/1.2977872View Description Hide Description
Spectral broadening in silicon through self-phase modulation is studied numerically and experimentally in the normal dispersion regime. Temporal dynamics of the free carriers generated during the propagation of optical pulses, through the process of two-photon absorption, affect the amplitude and phase of the optical pulses, thereby determining the nature and extent of the generated spectral continuum. Experimental results are obtained by propagating picosecond optical pulses in a siliconwaveguide for intensities that span two orders of magnitude . These results validate the conclusions drawn from numerical simulations that the continuum generation has a self-limiting nature in silicon.
Single-laser-shot detection of nitric oxide in reacting flows using electronic resonance enhanced coherent anti-Stokes Raman scattering93(2008); http://dx.doi.org/10.1063/1.2973166View Description Hide Description
Single-laser-shot electronic resonance enhanced coherent anti-Stokes Raman scattering (ERE-CARS) spectra of nitric oxide (NO) were generated using the 532 nm output of an injection-seeded Nd:YAG (yttrium aluminum garnet) laser as the pump beam, a broadband dye laser at approximately 591 nm as the Stokes beam, and a 236 nm narrowband ultraviolet probe beam. Single-laser-shot ERE-CARS spectra of NO were acquired in an atmospheric-pressure hydrogen/air counterflow diffusionflame. The single-shot detection limit in this flame was found to be approximately 30 ppm, and the standard deviation of the measured NO concentration was found to be approximately 20% of the mean.
Variable optical delays at using fast light in an InAs/InP quantum dash based semiconductor optical amplifier93(2008); http://dx.doi.org/10.1063/1.2973168View Description Hide Description
Room temperature optical variable delays are demonstrated using InAs/InP quantum dash semiconductor optical amplifiers (SOAs) at . A microwave frequency modulated single optical beam allows to demonstrate fast light through the achievement of maximum optical delays of 136 ps at 250 MHz and at 2 GHz by means of electrical control of the SOA bias current. The group index variation is attributed to enhanced nearly degenerate four wave mixing of this material system as well as population pulsation.
93(2008); http://dx.doi.org/10.1063/1.2978071View Description Hide Description
We demonstrate fast electrical modulation of freely propagating terahertz waves at room temperature using hybrid metamaterialdevices. The devices are planar metamaterialsfabricated on doped semiconductor epitaxial layers, which form hybrid metamaterial—Schottky diode structures. With an applied ac voltage bias, we show modulation of terahertz radiation at inferred frequencies over . The modulation speed is limited by the device depletion capacitance which may be reduced for even faster operation.
93(2008); http://dx.doi.org/10.1063/1.2978396View Description Hide Description
A polarization-switchable single photon source is demonstrated by embedding a self-assembled quantum dot in a high-quality, electrically gated, oxide-apertured micropillar cavity. Due to the noncircular aperture, the polarization degeneracy of the fundamental cavity mode is lifted, leaving two linearly polarized modes separated by . An intracavity electric field generated by an applied bias enables Stark shift tuning of the quantum dot emission over a frequency range containing both polarization modes, switching the dominant single photonpolarization through the Purcell effect. We measure polarization switching up to 300 kHz, limited by the time constant of the device.
93(2008); http://dx.doi.org/10.1063/1.2978069View Description Hide Description
Ultrafast two-color pump-probe measurements,time-resolvedphotoluminescence(TRPL), and photoluminescence excitation measurements were performed on Si-rich nitride (SRN) and Er doped SRN (Er:SRN) nanocrystals samples. Transient absorption data were compared with picosecond TRPL and excited state absorption cross (ESA) sections were measured at different wavelengths. Our data show that in Er:SRN, which is approximately at , does not scale with the behavior predicted by simple free carrier absorption models. Finally, our data demonstrate that in Er:SRN efficient energy transfer to Er ions occurs on the nanosecond time scale with reduced ESA compared to Er-doped oxide-based systems.
- PLASMAS AND ELECTRICAL DISCHARGES
Theoretical investigation of sheath expansion and implant fluence uniformity in enhanced glow discharge plasma immersion ion implantation93(2008); http://dx.doi.org/10.1063/1.2977962View Description Hide Description
In enhanced glow dischargeplasma immersion ion implantation that involves a small-pointed anode and large area tabular cathode, the high negative substrate bias acts as the plasma producer and supplies the implantation voltage. An electric field is created to focus the electrons and the electron-focusing field in turn enhances the glow discharge process. The sheath physics is theoretically investigated using numerical simulation based on the multiple-grid particle-in-cell code. Electron focusing is corroborated and the plasma sheath has enough expansion when so that a uniform distribution of the incident ion fluence is attained.