Volume 86, Issue 15, 11 April 2005
- 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
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
Pseudomorphic heterojunctionbipolar transistors (PHBTs) using a compositionally graded collector (10% indium grading) and graded base (6% indium grading) to reduce the transit time of the device are reported. A HBT achieves excellent values of (associated ) at a collector current density of , with a dc gain of 65 and a breakdown voltage of .
- LASERS, OPTICS, AND OPTOELECTRONICS
Intensity-modulated blue light generated by frequency doubling of wavelength-modulated high-power diode-laser radiation86(2005); http://dx.doi.org/10.1063/1.1899234View Description Hide Description
A scheme for the generation of modulated blue laser radiation is demonstrated. The radiation of a high-power diode-laser master-oscillator power-amplifier system is wavelength modulated within a range of by modulating the injection current of the distributed feedback (DFB)diodeoscillator. Single-pass frequency doubling of the generatedradiation in periodically poled potassium titanyl phospate converts the wavelength modulation into an intensity modulation with a contrast ratio exceeding 700:1. The modulation bandwidth of is limited by the speed of the wavelength tuning of the DFBoscillator.
86(2005); http://dx.doi.org/10.1063/1.1888052View Description Hide Description
An ultrafast all-optical switching is demonstrated in an organic three-dimensional nonlinear photonic crystal with a response time as short as 120 fs. The operating wavelength of the optical switching is in the visible spectrum. The switching function is realized by a shift of the photonic band gap under optical pumping. It is found that the photonic band gap shifts about 10 nm with the excitation of pump laser.
86(2005); http://dx.doi.org/10.1063/1.1897848View Description Hide Description
A mechanism for molecular negative ion (anion) formation under irradiation of neutral molecules by synchronized laser and electron pulses is considered. Numerical estimates are obtained for the efficiency of this process in cases of valence-bound and dipole-bound anions. The proposed mechanism allows, in principle, one to detect molecules with their absolute concentration at the level of corresponding to a relative concentration of under atmospheric pressure.
86(2005); http://dx.doi.org/10.1063/1.1900313View Description Hide Description
The spectral response of quantum-well infrared photodetectors(QWIPs) based on the III-V material system are tailorable to narrow or broad bandwidths within mid- and long-wavelength infrared bands. Typical broad-band QWIPs show considerable spectral shape change with bias voltage, particularly near the cut-off wavelength region. Two alternatives to the typical broadband QWIP design have been demonstrated. These designs consist of two multiquantum-well (QW) stacks or alternatively placed QWs and produce nearly fixed spectrums within the operating bias voltages. Flexibility in many design parameters of these detectors allows for tuning and tailoring the spectral shape according to application requirements, specifically for spectral imaging instruments.
Realization of inverse saturable absorption by intracavity third-harmonic generation for efficient nonlinear mirror mode-locking86(2005); http://dx.doi.org/10.1063/1.1899235View Description Hide Description
A technique of suppressing passive Q-switching by inverse saturable absorption in a cw nonlinear mirrormode-locked laser is presented. The nonlinear mirror saturable absorber consists of a second-harmonic generation crystal and a dichroic mirror while the inverse saturable loss is realized by intracavity third-harmonic generation. The inverse saturation reduces significantly the critical intracavity pulse energy for stable, self-starting, self-sustained, and power scalable cw mode-locking. Two crystals are employed to realize the technique in a diode array pumped oscillator providing a peak power of , pulse width of , and repetition rate of .
Optical loss and lasing characteristics of high-quality-factor AlGaAs microdisk resonators with embedded quantum dots86(2005); http://dx.doi.org/10.1063/1.1901810View Description Hide Description
Optical characterization of AlGaAs microdisk resonantcavities with a quantum dot active region is presented. Direct passive measurement of the optical loss within AlGaAs microdisk resonant structures embedded with dots-in-a-well (DWELL) is performed using an optical-fiber-based probing technique at a wavelength that is red detuned from the dot emission wavelength . Measurements in the wavelength band on microdisks of diameter show that these structures support modes with cold-cavity quality factors as high as . DWELL-containing microdisks are then studied through optical pumping at room temperature. Pulsed lasing at is seen for cavities containing a single layer of InAsdots, with threshold values of , approaching the estimated material transparency level. Room-temperature continuous-wave operation is also observed.
86(2005); http://dx.doi.org/10.1063/1.1901811View Description Hide Description
Effects of pulsed and continuous light illumination on field emission from CuO nanobelt arrays have been studied by using a transparent anode technique. It is found that, at low-field emission current level, the field emission current generally increases under a pulsed irradiation; at an emission current level of , a 19% increase in emission current was recorded. The photoinduced current increase is reduced with increasing emission current and is undetectable when the emission current is higher than . On the other hand, a long time illumination of the sample decreases the field emission current. Possible physical mechanisms behind the observed phenomena are discussed.
86(2005); http://dx.doi.org/10.1063/1.1899240View Description Hide Description
This work reports continuous laser oscillation around at room temperature in Nd:YAGplanar waveguidesfabricated by MeV protonimplantation. The performance of the waveguide lasersfabricated with different implantation parameters has been studied in terms of the threshold pump powers and slope efficiencies. These results have been compared with those obtained in Nd:YAGwaveguide lasers operating at a wavelength of , taking into account the different emission cross-sectional values of the and transitions.
86(2005); http://dx.doi.org/10.1063/1.1897061View Description Hide Description
We investigate the diffraction properties of sectioned multilayers in Laue (transmission) geometry, at hard x-ray energies (9.5 and ). Two samples are studied, a multilayer of periods, and a multilayer of periods, with cross-section depths ranging from . Reflectivities as high as 70% are observed. This exceeds the theoretical limit for standard zone plates operating in the multibeam regime, demonstrating that all of the intensity can be directed into a single diffraction order in small-period structures.
86(2005); http://dx.doi.org/10.1063/1.1901806View Description Hide Description
Ultrafast pump-probe experiments were used to study high-intensity ultrafast pulse-ablation dynamics in fused silica. Two laser pulses with varied time delay and pulse energy were used to irradiate fused silica samples and observe the transient reflectivity and transmissivity of the probe pulse. It was seen that the probe reflectivity initially increased due to the formation of free-electron plasma and then dropped to a low value within a period of about caused by a rapid structural change at the surface. The time-resolvedmeasurements of reflectivity and transmissivity were also related to atomic force microscopymeasurements of the depth of the laser-ablated hole. It was seen that the depth peaked at zero delay between the pulses and decreased within a period of about as the temporal separation between the pulses was increased caused by the screening by the plasma produced by the first pulse. When the temporal separation is about or longer, evidence for melting and resolidification during double-pulse ablation was also observed in the form of ridges at the circumference of the ablated holes.
room-temperature emission of square-lattice photonic-crystal waveguide lasers with a single line defect86(2005); http://dx.doi.org/10.1063/1.1905810View Description Hide Description
Narrow waveguides consisting of a single defect-line (W1) in a square lattice photonic crystal are fabricated on InP using the substrate approach. A single-mode distributed-feedback laser emission is obtained under optical pumping at room temperature. Lasing occurs at the second folding point of the dispersion curve of the fundamental waveguide mode (wave vector ). The emitted wavelength ranges from for a lattice period varying from and a constant air filling factor of . The highly monomode behavior is explained using two-dimensional plane-wave models. Similar experiments conducted on triangular lattice W1 waveguides do not yield a laser emission. Three-dimensional simulations confirm that triangular lattice W1 waveguides suffer higher losses than their square homologues.
86(2005); http://dx.doi.org/10.1063/1.1905812View Description Hide Description
The phase dependence of light reflected from colloidalphotonic crystals is measured using a large resonant cavity and self-assembled colloidalphotonic crystals. We measure the expected phase shift upon reflection from the photonic crystal, which varies from across the photonic crystal stop band. These measurements are then fed directly into the design of photonic crystal cavities. We obtain a measure for the precision needed in the fabrication of photonic crystal resonant cavities.
86(2005); http://dx.doi.org/10.1063/1.1900957View Description Hide Description
We have fabricated three-dimensional optically active ZnOphotonic crystals by infiltrating polystyrene opal templates using a low-temperature atomic layer deposition process. The polystyrene is removed by firing the samples at elevated temperatures, and reactive ion etching is used to remove the top layer of ZnO and expose the (111) photonic crystal surface. The resulting structures have high filling fractions, possess photonic band gaps in the near-UV to visible spectrum, and exhibit efficient photoluminescence.
86(2005); http://dx.doi.org/10.1063/1.1899747View Description Hide Description
Operation and imaging principles of optical microscope with in-plane image magnification by surface plasmonpolaritons are discussed. The influence of realistic experimental geometry and losses in the metal are considered. Using two-dimensional optics of surfacepolaritons on metal–dielectric interface, subwavelength optical resolution can be achieved with long-wave-vector surfacepolaritons and applied in far-field optical microscopy and photolithography.
86(2005); http://dx.doi.org/10.1063/1.1905804View Description Hide Description
Wave phenomena in a planar periodically corrugated waveguide are investigated experimentally at the microwave range of frequency. Measurements of the transmission properties show that the location of the gap in the frequency spectrum as well as its width depends on the relative position of two corrugated plates. The transmission varies from zero to a maximum value upon a shift of one periodic plate with respect to another on the half period of the corrugation. The results confirm the theoretical prediction of the geometry-driven spectrum transformation from a band-structure form to a gapless one upon such a shift of the plates. In physics of solids, this transformation corresponds to metal–insulator transition.
86(2005); http://dx.doi.org/10.1063/1.1905811View Description Hide Description
We demonstrate that broad-area vertical-cavity semiconductor optical amplifiers allow for wavelength conversion at via cross-gain modulation (XGM). XGM is reached with a saturation beam of only over an optical bandwidth of . Depending on the wavelengths of the injected fields, inverted or noninverted output can be obtained.
Pretransitional enhancement of the optical nonlinearity of thin dye-doped liquid crystals in the nematic phase86(2005); http://dx.doi.org/10.1063/1.1905796View Description Hide Description
We report a critical enhancement of the nonlinear optical response of dye-doped liquid crystals obtained by approaching the clearing point in the nematic phase. The enhancement of the nonlinear diffraction efficiency has been measured in the range 0.2–0.3 deg below the nematic-isotropic transition temperature. It allows reaching a nonlinear refractive index higher than in all the tested cells.
High-efficiency quantum-dot microcavity light-emitting diodes grown by metalorganic chemical vapor deposition86(2005); http://dx.doi.org/10.1063/1.1898440View Description Hide Description
We investigate the optical properties of quantum-dot (QD)microcavity light-emitting diodes (MCLED) operating at at room temperature. The active medium consists of a single layer of InGaAsquantum dots, directly grown in a GaAs matrix by metalorganic chemical vapor deposition. Electrical injected QD MCLEDs were fabricated by exploiting a hybrid technology, which employs epitaxial and oxide-based mirrors. Such technology allows us to preserve the QDproperties and leads to a wider optical bandwidth of the hybrid top distributed Bragg reflector with respect to the fully epitaxialmirror, resulting in photon recycling of the overall QDs spectrum, thus improving the efficiency of the device. The devices exhibit bright electroluminescence peaked at , with a full width at half maximum of 10 meV. The room-temperature external quantum efficiency of such devices is 0.52%, higher than that reported in the literature for QD MCLEDs operating at at room temperature.
86(2005); http://dx.doi.org/10.1063/1.1905781View Description Hide Description
We demonstrate a cavityoptimization method for efficient optical pumping of a semiconductor microcavity. An enhanced pumping efficiency makes it possible to pump broad-area microcavities for, e.g., high-power lasers or parallel optical processing of information. This is especially important in the near-infrared where a pump not absorbed into the active material is absorbed into the substrate and converted into heat. We apply the method to optical pumping of a diameter laser with a spatially uniform pump profile. This method could also prove useful for the design of vertical external cavity surface emitting lasers.
86(2005); http://dx.doi.org/10.1063/1.1900946View Description Hide Description
In this Letter, the thermal stability of GaInAsSb grown by molecular-beam epitaxy was investigated. We found a strong blueshift for both bulk material and multiple-quantum-well(MQW) structures caused by thermal annealing. The shift is almost independent of design parameters such as indium concentration, strain, and growth parameters such as temperature. For a -thick GaInAsSb bulk layer, a blueshift of was found after annealing for at , whereas for MQW structures the maximum shift was .