Volume 94, Issue 3, 01 August 2003
- lasers, optics, and optoelectronics (pacs 42)
- plasmas and electrical discharges (pacs 51-52)
- structural, mechanical thermodynamic, and optical properties of condensed matter (pacs 61-68, 78)
- electronic structure and transport (pacs 71-73)
- magnetism and superconductivity (pacs 74-76)
- dielectrics and ferroelectricity (pacs 77)
- nanoscale science and design
- device physics (pacs 85)
- applied biophysics (pacs 87)
- interdisciplinary and general physics (pacs 1-41, 43-47, 79, 81-84, 89-99)
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
94(2003); http://dx.doi.org/10.1063/1.1586960View Description Hide Description
Sulfur passivation of GaInAsSb photodetectors was studied in terms of Auger electron spectroscopy and x-ray photoelectron spectroscopy. The experimental results showed that Sb–S and In–S bonds exist on the sulfur-passivated GaInAsSb surfaces. The reverse dark current of the photodetectors was reduced and the peak detectivity reached after passivation.
94(2003); http://dx.doi.org/10.1063/1.1587269View Description Hide Description
Highly stable polarizationgratings have been prepared in photocrosslinkable polymerliquid-crystalfilms by the use of two orthogonally polarized He–Cd laser beams and subsequent annealing. The resulting pure polarizationgratings exhibiting thermal stability up to 150 °C diffract the beam and convert the polarization state at the same time according to the theoretical expectation.
94(2003); http://dx.doi.org/10.1063/1.1589596View Description Hide Description
Three-dimensional optical recording of high contrast spherical bits (diameter<300 nm) at a density of 500 G/cm3 in fused silica using a Ti:sapphire femtosecond laser is demonstrated. Bits are optically read out using both a confocal and a phase-contrast scheme. The recording density for different materials and recording mechanisms are discussed.
Two-dimensional phononic crystal with tunable narrow pass band: Application to a waveguide with selective frequency94(2003); http://dx.doi.org/10.1063/1.1557776View Description Hide Description
We study theoretically the propagation of elastic waves in two-dimensional composite media composed of a square array of hollow steel cylinders embedded in water using the finite-difference time-domain method. These composite media constitute a class of acoustic band gapmaterials with narrow pass bands in their transmission stop bands. The frequency at which the pass band occurs is tunable by controlling the inner radius of the tubular steel inclusions. The effect of the tube inner radius on the transmission spectrum is semiquantitatively separable from the effect of the composite periodicity. A linear defect formed of a row of hollow cylinders in an array of filled cylinders produces an elastic waveguide that transmits at the narrow pass band frequency. We show that two of these tunable waveguides with different inner radii can be employed to filter and separate two specific frequencies from a broad band input signal.
Theory of the mode stabilization mechanism in concave-micromirror-capped vertical-cavity surface-emitting lasers94(2003); http://dx.doi.org/10.1063/1.1586962View Description Hide Description
We have investigated theoretically the transverse mode stabilization mechanism in oxide-confined concave-micromirror-capped vertical-cavity surface-emitting lasers (CMC-VCSELs) as reported by Park et al. [Appl. Phys. Lett. 80, 183 (2002)]. From detailed numerical calculations on a model CMC-VCSEL structure, we found that mode discrimination factors appear to be periodic in the micromirror layer thickness with a periodicity of λ/2. We also found that there are two possible concave micromirror structures for the fundamental transverse mode laser operation. These structures can be grouped according to the thickness of the concave micromirror layer: whether it is an integer or a half-integer multiple of λ/2. The optimal micromirror curvature radius differs accordingly for each case. In an optimally designed CMC-VCSEL model structure, the fundamental transverse mode can be favored as much as 4, 8, and 13 times more strongly than the first, second, and third excited modes, respectively.
94(2003); http://dx.doi.org/10.1063/1.1587891View Description Hide Description
-doped sinteredceramics were prepared in vacuum and in air. It was shown that the vacuum-sintered disks are able to store energy when irradiated with 300-nm or shorter photons. A small part of the stored energy could be recovered with 980-nm light. A much more significant amount of the stored energy could be released with red 647-nm photons. However, recovering the total stored energy could be accomplished only upon heating up to about 300 °C. Changes in absorption of the raw materials upon ultraviolet irradiation and subsequent IR (980 and 647 nm) treatments or upon heating at 300 °C are presented and discussed. A model for energy storing and recovering through the various IR irradiations or through heating is presented. At least two distinct ways of hole trapping as or -center as well as creation of F and is suggested.
Spectral components and their contributions to the 1.5 μm emission bandwidth of erbium-doped oxide glass94(2003); http://dx.doi.org/10.1063/1.1586958View Description Hide Description
In this article, the 1.5 μm emission spectra corresponding to the transition of in oxide glass are studied within the temperature from 11 to 300 K. The spectral components emitting from the lowest and upper Stark levels of the state are analyzed and separated. The effect of the spectral components on the 1.5 μm emission bandwidth is investigated. The results indicate that to search a host with higher spontaneous emission probability of the upper Stark levels of the state for ions is very important to broadening of the 1.5 μm emission band of An equivalent model of the four-level system is presented and applied to explain the spectral shape and temperature characteristics of the 1.5 μm emission band. According to the theory of McCumber, we transform the absorptionspectrum into the emission spectrum, the shape of which fits well to that measured.
Ultrabroad-band phase matching in two recently grown nonlinear optical crystals for the generation of tunable ultrafast laser radiation by type-I noncollinear optical parametric amplification94(2003); http://dx.doi.org/10.1063/1.1591074View Description Hide Description
It was found that the generation of ultrabroad-band femtosecondpulsed laser radiation is possible in two recently grownnonlinear optical crystals, (KABO) and (CLBO), by employing a type-I noncollinear optical parametric amplification (NOPA) scheme, pumped by Ti:sapphire second harmonic (395 nm) radiation. The phase-matching bandwidths of the process are as large as 152 and 164 THz in KABO and CLBO crystals, with the values of the noncollinear angles (α) between pump input (considered monochromatic) and seed pulses input are 3.3° and 3.0°, respectively. The phase-matching bandwidth calculated for the same type-I NOPA in BBO crystal is 157 THz with In addition to the large phase-matching bandwidth in CLBO, the major advantages of this crystal are that it can easily be grown to large sizes and it also has a higher threshold against laser damage. The most attractive properties of KABO crystal are that it is nonhygroscopic as well as mechanically robust and easy to cut and polish. Having moderate birefringence the angular and spectral bandwidths of both CLBO and KABO crystals are larger than that of BBO crystal and the deleterious walk-off angles are smaller than that of BBO. The walk-off angles at the pump wavelength of NOPA with CLBO, KABO, and BBO crystals are about 2.1°, 2.7°, and 4.0°, respectively. Here we present the nonlinear optical parametric properties of CLBO and KABO crystals for the generation of ultrabroad band femtosecond laser radiation by the NOPA technique, since we know of no such report so far in the literature.
94(2003); http://dx.doi.org/10.1063/1.1586469View Description Hide Description
Two optimized methods for accurately measuring the 1.5 μm lifetime of in crystals and waveguides are proposed. The first method, suitable for measurement of bulk material, was suggested by forming an annealedproton exchanged sandwich structure and fluorescence was collected through an adjustable aperture. This excitation collection scheme was used to investigate bulk Er-doped crystals with eight different doping levels, three different crystal thicknesses, and three different cut orientations. The 1.5 μm lifetime was investigated in three configurations: with both a sandwich and an aperture, with a sandwich but without an aperture, and without not only a sandwich but also without an aperture. In addition, the effect of the aperture was also studied. The second method, suitable for a waveguidestructure, was proposed on the basis of transversely gathering the fluorescence aided by an outcoupling fiber. It was optimized by comparing three different fluorescence collection schemes. Using this method, the lifetimes of some strip waveguides were measured. In addition, the effect of radiation trapping on the polarized fluorescencespectrum was also investigated. The experimental results are discussed and summarized.
94(2003); http://dx.doi.org/10.1063/1.1586974View Description Hide Description
We have studied how the photoluminescence (PL) and lasing characteristics of mid-IR type II “W” structures depend on the molecular beam epitaxygrowth conditions. The growth temperature that yields the highest PL intensities and narrowest PL lines is found to be in the ≈480–510 °C range, which is considerably higher than the temperatures used in previous type II antimonide laser growths. Also contrary to earlier reports is our observation that using migration-enhanced epitaxy to force an InSb-like interface bond type is detrimental to the laser performance. The PL intensity at 78 K is found to correlate closely with the PL intensities and linewidths at all temperatures, as well as the lasing linewidths, thresholds, and efficiencies. Even though the tested laser structures were grown at a nonoptimal lower substrate temperature of 425 °C, they nonetheless yielded much better morphology, better-resolved x-ray features, stronger PL intensities, narrower PL linewidths, lower lasing thresholds (<200 W/cm2 at 78 K), lower internal losses (<5 cm−1 at 78 K), and longer Shockley–Read lifetimes (>20 ns at 78 K) than any previous antimonide lasers grown on the present Riber 32P molecular beam epitaxy system.
Photobleaching and optical properties of organic crystal 4-N, N-dimethylamino-4′-N′-methyl stilbazolium tosylate94(2003); http://dx.doi.org/10.1063/1.1588359View Description Hide Description
Photobleaching of organic optical materials can be used to structure the surface layer for integrated optics applications. Linear optical properties and absorption were studied in 4-N, N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST) organic crystals within the absorption band from 260–700 nm in order to determine the depth-range of photobleaching. The results were obtained from reflectivity measurements and bleaching experiments. The depth range of photobleaching can be varied between 0.2 and 2.6 μm by selecting a suitable wavelength.
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
94(2003); http://dx.doi.org/10.1063/1.1588351View Description Hide Description
The behavior of species in the gas phase and their effects on the etchingcharacteristics of organic film with the lower dielectric constant (low-k) were investigated in 500 MHz ultrahigh frequency (UHF) plasma using and gases. The absolute H and N radical densities and molecule density in etchingplasmas were evaluated by the vacuum ultraviolet absorption spectroscopy and the infrared diode laser absorption spectroscopy technique, respectively. The effects of frequency that excited the plasma in the production of H and N radicals were clarified by comparing the behavior of radicals in the UHF plasma with that in the inductively coupled plasma(ICP) exciting at the frequency of 13.56 MHz reported in the previous study. H radicals were produced more efficiently from gas and N radicals more efficiently from gas in the UHF plasma than in the ICP. H radicals were generated not only through the dissociation of the molecule but also from molecules produced in the plasma. On the other hand, the N radical density was lower by one order of magnitude than the H radical density, and was seldom produced from the molecule. It was found that the etch rate and etched profile could be controlled with an internal plasma parameter of the ratio of the H and N radical densities under the constant electron density in the plasma gas chemistry of both and The optimal conditions for the anisotropic profile and high etch rate were well determined by the ratio of the H and N radical densities and the substrate temperature. The results of this study are very useful not only for understanding the fundamental process of organic low-kfilmetching but also for precisely controlling the etching process.
94(2003); http://dx.doi.org/10.1063/1.1586989View Description Hide Description
The spatial distributions of the trappingdust particles under the interaction of the electrostatic, gravitational, ion-drag, and pressure gradient forces in a radio-frequency sheath are investigated with a self-consistent model. The effects of the trappingdust particles on the ion flux, ion mean velocity, ion and time-averaged electron densities, and time-averaged local potential in the sheath are studied in detail. The distribution for the particles with a finite temperature has a thermal broadening. The region where dust particles trapped is wider for a higher dust temperature or a smaller particulate radius. Due to the collection and scattering of ions by dust particles, the ion flux in the sheath with dust suspending is not constant but decreased. The ion and time-averaged electron densities in the region of trapping particles are also decreased. The time-averaged local sheath potential in the region of the trappingdust particles is even more negative and the local ion mean velocity is increased, which are qualitatively consistent with the experimental measurements of Arnas et al. [Phys. Plasmas 7, 4418 (2000)].
94(2003); http://dx.doi.org/10.1063/1.1587889View Description Hide Description
A theoretical approach has recently been described [Z. Sternovsky, S. Robertson, and M. Lampe, Phys. Plasmas 10, 300 (2003)] for including the effect of ion collisions in the orbit motion limited theory for cylindrical Langmuir probes. In plasmas with a single ion species, ion-neutral charge exchangecollisions are dominant and their first order effect is to increase the magnitude of the collected ion current. Measurements in Ar and Ne gas discharges at plasma densities show that the theory is accurate only for probes with radii less than approximately half the Debye length. For larger probes, absorption of ions at the probe surface reduces the ion density locally causing the sheath to expand. This increases the volume from which the charge exchange ions are collected and further increases the ion current. Poor agreement between measurements and theory is also found, when the probe is placed close to the ionization source.
94(2003); http://dx.doi.org/10.1063/1.1586978View Description Hide Description
Hexafluoro-1,3 butadiene is a potential etching gas with a very low global warming potential for the manufacturing of semiconductors, unlike commonly used fluorocarbon gases such as and We report ion energy distributions, relative ion intensities and absolute total ion current densitiesmeasured at the edge of an inductively coupled gaseous electronics conference radio-frequency reference cell for discharges generated in pure and mixtures. In addition, the ratio of radical densities relative to CF measured using submillimeter absorption spectroscopy and optical emission spectroscopymeasurements are presented. These measurements of the plasmas were made for several different gas pressures (0.67, 1.33, and 2.66 Pa) and gas mixture ratios (25%, 50%, 75%, and 100% volume fractions).
94(2003); http://dx.doi.org/10.1063/1.1589592View Description Hide Description
The formation of the double layer created around the anode in magnetized radio frequency inductively coupled plasma, which is visually apparent because of enhanced light emission from the neutrals excited by energetic electrons, is investigated in detail in this work. The effects of the external magnetic field and anode voltage on the evolution of a cylindrical luminous anodedouble layer from the anodeglow are evaluated in magnetized hydrogen plasmas. The anodeglow is initially produced by the additional dc discharge which forms when a cylindrical anode inserted into the plasmadiffusion region is positively biased. If the anode voltage is sufficiently high, the anodeglow is transformed into an elongated luminous anodedouble layer in the plasmadiffusion region, to which a diverging magnetic field generated by external magnetic coils is coupled. A weakly magnetized plasma is needed for the formation of the anodedouble layer in our experiments, and there is a magnetic field strength ceiling beyond which the anodedouble layer disappears. The dependence of the anodedouble layer structure on the magnetic field strength, anode voltage and the neutral gas pressure is also investigated.
94(2003); http://dx.doi.org/10.1063/1.1589172View Description Hide Description
A current–voltage characteristic of one-side planar and cylindrical probes was considered for the use in the determination of plasma parameters when the electron velocity distribution functions (EVDFs) were significantly anisotropic. The EVDFs, space potential, and rates of inelastic process in pulse modulated and stratified discharges were obtained. The results obtained using the exact and simplified method were compared. It was also shown that only a simplified method gives satisfactory results in the wide range of discharge conditions. Some discrepancies between theoretically determined and measured potentials in homogeneous plasma were found. A procedure, which allows for exact determination of space potentials, was given.
94(2003); http://dx.doi.org/10.1063/1.1589597View Description Hide Description
High-pressure plasma discharge columns that are long and straight, as well as uniform in the axial direction, have been generated in a steady state. These discharges, stabilized by rotation of the containment envelope about a horizontal axis, have reduced heat transport to the wall due to the absence of buoyancy-driven radial convection and the elimination of eddies caused by sheared flow. These “rotating tube discharges” may take the form of electric arcs powered with dc or low-frequency ac; or of electrodeless plasmas, heated by electromagnetic waves at rf or microwave frequencies.
94(2003); http://dx.doi.org/10.1063/1.1590054View Description Hide Description
Ion current distribution in a system with crossed magnetic and electrical fields for plasma immersion ion implantation has been investigated. It is found that the ion current to a target has a nonmonotonic behavior with bias voltage when a magnetic field is applied. For instance, the current density has a maximum of about 150 A/m2 at bias voltage of about 1 kV in the case of a magnetic field parallel to the target of about 0.035 T. These results are explained in terms of ionization by magnetized electrons in the system. Our findings suggest that the system with crossed fields can be used for intense plasma immersed processing.
94(2003); http://dx.doi.org/10.1063/1.1591079View Description Hide Description
We describe the temporal development of the plasma composition in a pulsed plasma stream generated by cathodic arc. Cathodes of Zr and Cr were operated at various nitrogen pressures. The time-resolved plasma composition for the cathodematerials was analyzed with time-of-flight charge-to-mass spectrometry, and was found to be a strong function of the nitrogen pressure. Large plasma composition gradients were detected within the first 60 μs of the pulse, the nitrogen ion concentration increasing with increasing pressure. The results are explained by the formation and erosion of a compound layer formed at the cathode surface in the presence of a reactive gas. The average charge state was also found to be affected by the reactive gas pressure as well as by the time after ignition. The charge states were highest in the beginning of the pulse at low nitrogen pressure, decreasing to a steady-state value at higher pressure. These results are of importance for reactive plasma processing and for controlling the evolution of thin film composition and microstructure.