Showing papers on "Power density published in 1990"

A new DFB-laser diode with reduced spatial hole burning

Abstract: An index coupled antireflection-coated distributed-feedback (DFB)-laser diode which theoretically exhibits a longitudinally uniform power density is proposed. The structure contains an amplitude modulated grating and is far more efficient in reducing spatial hole burning than multiphase-shift lasers. The laser can be expected to be single mode up to high power levels. It can be of interest when long lasers with a reduced linewidth and a flat FM response are to be used or as a laser with small modulation distortion in analog communication. >

Ultrahigh power efficiency operation of common-emitter and common-base HBT's at 10 GHz

Abstract: The DC and RF characteristics of microwave power HBTs are described. Ultrahigh power-added efficiency is reported for AlGaAs-GaAs HBTs operating at 10 GHz in common-emitter (CE) and common-base (CB) modes. A record high 67.8% power-added efficiency with 11.6 dB associated gain was achieved with a CE HBT at a CW output power of 0.226 W, corresponding to a power density of 5.6 W/mm. With a CB HBT, 62.3% power-added efficiency with 11.85 dB gain and 0.385 W total CW power was demonstrated. Power saturation characteristics of CE and CB HBTs are compared. The importance of bias schemes is discussed. High-efficiency operation in near class B mode is described and compared with FET operation. An advantage of HBT over FET is the low leakage current during the off half cycle in class B operation. Stability conditions for CE and CB HBTs are discussed. >

Particulate generation in silane/ammonia rf discharges

Abstract: The rate of particle generation in a SiH4/NH3 rf discharge has been studied as a function of the discharge operating parameter space, electrode geometry, and power supply coupling mode. Measurements of the bulk quantity of particles produced in the discharge reveal that the mode of coupling (capacitive or dc) as well as the electrode temperature significantly affects particle generation rates. Laser light scattering measurements made as a function of the plasma power density indicate that particle generation abruptly ceases at a threshold value sufficient to induce spark breakdown at the cathode. Based on these observations, it is shown that particle growth in plasmas can be modeled entirely as a heterogeneous process. The initiation of particle growth is shown to be consistent with an electron surface desorption model involving vibrational excitation of surface clusters. Propagation of growth in the gas phase is shown to be consistent with an eliminative ion‐molecular condensation reaction, and the press...

Design fundamentals of high power density, pulsed discharge, lead acid batteries. I, Experimental

Abstract: In this paper the design of a battery with maximum specific power to be discharged for 0.01 s or less is explored. Key elements of the design are bipolar construction, using thin components with high electronic conductivity in the bipolar separator and high ionic conductivity in the electrolyte, and the use of an electrochemical couple with high open-circuit potential and fast electrode kinetics. Bipolar lead-acid stacks were assembled which showed specific powers of 100--800 kW/kg with current densities of up to 10--40 A/cm{sup 2} for up to 100 {mu}s. Single lead-acid cell tests showed that acid concentration, separator thickness and conductivity, discharge potential, and PbO{sub 2} formation time all had a major impact on the cell power output. Tests showed that these cells are capable of well over a million shallow discharge/charge cycles. Evidence indicates that PbSO{sub 4} formation severely reduces cell current densities after 200--400 {mu}s of discharge. In the first 200 {mu}s, H{sub 2}SO{sub 4} concentration depletion at the reaction interface appears to be a factor in current decline.

An InP MISFET with a power density of 1.8 W/mm at 30 GHz

Abstract: The millimeter-wave power performance of a 75- mu m*0.3- mu m InP MISFET with SiO/sub 2/ insulator is presented. The combination of high intrinsic transconductance (120 mS/mm), current density (1 A/mm), and gate-source and gate-drain breakdown voltages (35 V) led to a record power density of 1.8 W/mm and 20% power-added efficiency at 30 GHz. This power density is the highest ever reported for any three-terminal device at this frequency. >

Indocyanine Green Dye Enhanced Vascular Welding With the Near Infrared Diode Laser

Abstract: For vascular anastomosis, use of topical photosensitizing dye enhances selec tive delivery of laser energy to target tissue, thus reducing the amount of collat eral thermal injury and threshold power required for welding. The authors compared the threshold power density needed to weld abdominal aortotomies in rabbits with and without photosensitizing dye. With continuous wave diode la ser energy, the threshold for welding using the dye indocyanine green (ICG) was 150 mW (power density 4.8 watts/cm2 at spot diameter of 2 mm). Without dye enhancement, tissue effects were not observed even at the highest energy output available from the laser (300 mW, power density 9.6 watts/cm2). Immediately after welding, the mean bursting pressure for the welds was 260 mm Hg. In survival studies, no anastomotic ruptures, thomboses, or aneurysms were iden tified. Use of photosensitizing dyes for tissue welding is feasible and may allow arterial welding with lower power laser systems and cause less thermal trauma by lowerin...

Application of the GaSb solar cell in isotope-heated power systems

Abstract: It is pointed out that, with the technical advancement of the GaSb solar cell, a radioisotope thermophotovoltaic (RTPV) generator will become very competitive compared with thermoelectric systems. The required cell characteristics and the impact which RTPV operation would have on isotope power system design are discussed. Using a computer model of the GaSb cell and various candidate radioisotopes within a reflective cavity, the efficiency, overall power, and power-to-weight ratios were calculated. Test results for current cells are also presented which support the predictions for power output. It is shown that, with existing /sup 238/Pu heat sources operating at 1100 degrees C, a 573 W system should operate at 14.4% efficiency and exhibit a system-level specific power of approximately 9.2 W/kg. Isotopes with higher power densities such as /sup 244/Cm could yield efficiencies of 20% and specific powers exceeding 60 W/kg. >

A compact DC-to-DC power converter for distributed power processing

Abstract: A compact (55 W/in/sup 3/), efficient (86% power train), 1 MHz switch-mode, DC-to-DC power converter contained in a 2 in by 2 in by 0.25 in, 1 in/sup 3/ inch package is presented. The converter developed for on-card applications in distributed power processing systems, uses pulse-width modulation at a constant frequency of 1 MHz (2 MHz ripple frequency) and zero-voltage resonant transition switching. The interleaved forward topology, steady-state analysis, capacitor substrate, planar printed-wiring-board transformer, packaging, electrical performance, power loss analysis, thermal analysis, reliability, and efficiency and power density improvements are described. >

Manufacture of thin film transistor

Abstract: PURPOSE:To prevent an impurity non-crystalline semiconductor from being exfoliated by forming an impurity non-crystalline semiconductor film using specific high frequency plasma discharge. CONSTITUTION:An impurity non-crystalline semiconductor film 5 interposed between a non-crystalline semiconductor film 4 and drain-source metal films 6, 7 is formed using 100kHz-20MHz high frequency plasma discharge with 7.5-18.8mW/cm RF discharge power density. From a relationship between the RF power density and stress, the possibility of the impurity doped non-crystalline semiconductor film being exfoliated from the active layer non-crystalline semiconductor film is more reduced, as RF power density becomes smaller. Hereby, the impurity non-crystalline semiconductor film can be prevented from being exfoliated to restrict any TFT defect.

Intense laser-induced electron emission from prepoled lead-lanthanum-zirconium-titanate ceramics

Abstract: A sample of lead‐lanthanum‐zirconium‐titanate (PLZT 9/65/35) has been exposed to 6‐ns‐long laser pulses of 266 nm wavelength. The maximum output pulse energy of the laser beam was 300 μJ, the output power density on the sample 5×105 W/cm2, and the beam diameter 3 mm. By applying a moderate extraction voltage of several kilovolts, intense electron beam pulses are emitted from the free sample surface. Their time structure corresponds to the time structure of the laser pulse. Electron beam current intensities of up to 0.1 A and 2 A/cm2 and total charges of 1 nC (corresponding to 20 nC/cm2 ) were measured with a simple Faraday cup. In the range where the parameters of laser intensity and of extraction voltage could be varied their influence on the emitted electron beam current amplitude was determined.

High-power CW operation of broad area InGaAlP visible light laser diodes

Abstract: Broad area InGaAlP visible light laser diodes with antireflection and high-reflection coatings have been fabricated. High power cw operation above 300 mW was obtained at 2°C heat-sink temperature. This value corresponded to a light power density of 2.7 MW/cm2. The far field pattern showed a single lobe shape for output power up to 100 mW.

Harmonic tuning of power FETs at X-band

Abstract: A study is presented of high-efficiency, harmonic-tuned, class-B operation of power MESFETs at X-band. Hybrid, single-stage 1200- mu m power FET (field-effect transistor) amplifiers were fabricated with the output circuit designed to provide optimum load impedance at the fundamental frequency (10 GHz) and short at the second harmonic. Power-added efficiency of 61% at an output power level of 450 mW and 7-dB power gain were obtained at 10 GHz. The corresponding drain efficiency was 75%. The second harmonic level in the output was suppressed to less than -40 dBc over a 4% frequency bandwidth. The efficiency was improved at the expense of a lower operating voltage and power density (0.4 W/mm) when compared with class-A or class-AB amplifiers made from similar devices. Theoretical harmonic-balance analyses of these tuned class-B amplifiers were also performed, and the results agree fairly well with the measured data. >

Fast axial flow CO/sub 2/ laser excited by silent discharge

Abstract: A fast axial flow CO/sub 2/ laser excited by silent discharge has been developed. With a new electrode system applied to the laser, homogeneous discharge of power density of up to 80 W/cm/sup 3/ is obtained without applying any stabilization techniques on the discharge. An output laser power of 920 W in stable TEM/sub 00/ mode operation is attained with an efficiency of over 14%. Beam fluctuation common to fast axial flow lasers is suppressed by the combination of smooth gas flow and low CO/sub 2/ molar fraction. >

Hybrid electric traction system - comprises electric motor, accumulator and high temp. fuel cell with mixed conductor electrodes

Abstract: The fuel cell may employ a liq. and/or solid fuel, e.g. petrol, diesel fuel, fuel oil, lower alkoxides or coal dust. Pref. the fuel cell is a hydrogen/oxygen fuel cell. The accumulator is pref. a sodium/sulphur accumulator with a short term power density of at least 100W/kg and an energy density after one hour discharge of at least 60W/kg. ADVANTAGE - Reactions take place over entire surface of electrodes, resulting in higher current densities so that, for a specified motor power, a fuel cell of considerably smaller total volume and wt. can be used. Energy densities of more than 200 (pref. more than 300, and esp. more than 500) W.hr./kg. can be attained.

Evaluation of trade-offs in transformer design for very-low-voltage power supply with very high efficiency and power density

Abstract: Design methodology and trade-offs have been presented for a transformer in low-voltage (1.5-5 V) power supplies intended to meet 95% efficiency and 100 W/in/sup 3/ power density. The design is based on the pot core geometry, which has low core loss, and the planar toroidal winding geometry, whose mechanical and electrical parameters are highly controllable and reproducible by modern fabrication processes. To achieve high power density in the presence of skin and proximity effects, the primary and secondary winding layers are interleaved to increase the effective thickness. Leakage inductance is reduced, and winding capacitance is increased as a result. The design equations have been coded into a computer program that selects the transformer with the lowest volume over specified ranges of optimizing parameters, such as power loss and flux density. >

Enhancement of Proton Stopping Power on Two-Dimensionally Focused "Plasma Focus Diode"

Abstract: Ion beam-target interaction experiments were performed by using a two-dimensionally focused “plasma focus diode”. The proton energy losses in different targets were measured with an improved time-resolvable Thomsonparabola energy spectrometer. With the beam power density of ∼0.1 TW/cm2 at a beam energy of ∼1.5 MeV, enhanced energy deposition has been observed for aluminium targets 7 µm thick. Theoretical calculations show that the experimental data are in good agreement with those given by the simulation model based on free and bound electron stopping terms.

High-power 780 nm window diffusion stripe laser diodes fabricated by an open-tube two-step diffusion technique

Abstract: High-power and low-threshold-current GaAlAs lasers with a simple window structure fabricated by controllable open-tube two-step diffusion and single-step metalorganic chemical vapor deposition are discussed. The window structure and the waveguide with a narrow width around 2 mu m are formed by diffusion of zinc, which just passes through an n-type active layer. CW output power up to 134 mW without catastrophic damage and a threshold current of 17 mA have been achieved. A maximum output power density of 16 MW/cm/sup 2/ is estimated. A stable fundamental transverse mode of up to 100 mV in the wavelength range of 780 nm is obtained. Excellent uniformity of device characteristics is confirmed. >

Barkhausen jump correlations in thin foils of Fe and Ni

Abstract: The Barkhausen noise emanating from the surface of thin foils of nearly pure iron and nickel was obtained by digitizing the noise signal over a complete hysteresis loop. This digitized signal is used to analyze various attributes of the noise such as the autocorrelation, power density spectrum, jump amplitude spectrum, and jump amplitude correlation. For thin foils (25 μm) the power density exhibits a peak in the low‐frequency range, contrary to what is predicted for a series of statistically independent Barkhausen jumps. Return maps and plots of jump amplitude versus time between jumps show no evident deviation from random noise behavior. Thus jump correlations or clustering do not explain the power density spectra, and an additional mechanism for the loss of low‐frequency power is required.

Laser cutting of glass ceramic matrix composite

Abstract: The laser cutting of a glass ceramic matrix composite containing about 50 vol.-% aligned SiC fibres has been investigated. A 2 kW CW (continuous wave) CO2 laser equipped with an x–y table was used with varying beam diameter, power, and table speed to give a range of processing conditions. The dimensions (depth and width) of the cuts were measured as a function of the processing conditions and the cut surfaces were examined using scanning electron microscopy and X-ray diffraction. Full through-section cuts, having vertical sides? were obtained using a narrow 1mm diameter beam operating at a (power density) / (table velocity) ratio in excess of approximately 30 J mm−3. The surface condition after laser cutting was superior to that obtained using conventional diamond sawing.MST/1168

Nuclear-driven solid-state lasers

Abstract: Mark A. Prelas and Frederick P. Boody Fusion Studies Laboratory, University of Missouri-Columbia 323 Electrical Engineering, Columbia, MO 65211 USA A new class of visible excimers are potential pumping sources for solid-state lasers such as Nd:Glass, GGG, GSGG, Alexandrite, and Emerald. These fluorescence sources are based on alkali excimers. The alkali metals have very low ionization potential and the excimer lines are in the visible. Hence, the alkali excimers have high intrinsic efficiencies (i.e., T\int = hv/W*). Calculations of potential laser efficiencies indicate that nuclear-driven alkali excimer flashlamps are competitive with semiconductor laser pump sources. Some experimental evidence for remotely pumping solid-state lasers will be presented to support the concepts described in this paper. Introduction Nuclear-Pumped Lasers (NPLs) directly interface with the ions created in nuclear reactions such as fusion and fission. Experimental investigations have resulted in the discovery of 18 NPLs [Prelas, Boody, Miley, & Kunze, 1988]. The major limitation of directly interfacing ions from nuclear reactions with lasers is the maximum power density available [Prelas, Boody, Miley, & Kunze, 1988]. One method of overcoming the power density limitations of directly interfacing the ions from nuclear reactions to lasers is to directly interface the ions to a medium which can store molecular energy [Wessol, Prelas, Merrill, & Speziale, 1988] or which can produce narrow band fluorescence [Prelas, Boody, Miley, & Kunze,, 1988]. The advantage of either method is that resonance transitions can be excited, thereby lowering the power density threshold of a potential laser medium. Miley, 1984, reported on a technique which utilizes 02(lA) as a molecule for energy storage and Boody and Prelas, 1983, reported on a technique which uses Xe2* excimer fluorescence to photolytically drive the XeF(B-X) laser. Laser Interaction and Related Plasma Phenomena, Vol. 9 Edited by H. Hora and G.H. Miley, Plenum Press, New York 197 This paper focuses on the use of nuclear generated visible narrow band fluorescence sources which can be used to drive solid-state lasers [Prelas, et. al., 1988] and the applicability of such lasers for inertial confinement fusion drivers. Nuclear-Driven Solid-State Lasers The keys to achieving solid-state lasers with multi-megawatt average power output are the pumping geometry and the pumping source. To ensure beam quality, the pumping geometry must be one that produces thermal gradients only in the direction of propagation, i.e. a large diameter thin disk, insulated on the edge and uniformly illuminated and cooled on the face. The then unavoidable axial gradient can be minimized by keeping the disk very thin and pumping steady state, so as to produce the lowest ma.Ximum temperature possible. The effects of the minimized axial gradient are themselves minimized by double passing through the laser medium. The ~ump source must be efficient and affordable and able to uniformly illuminate the laser medium under the above geometrical and temporal restraints. Geometry has been a problem because large diameter disks have been available only in Nd:glass, which has a high saturation intensity, narrow absorption bands, and poor thermal conductivity. Nd:YAG has much better laser and thermal properties, but even narrower absorption bands and can not be grown in large diameters. Pump sources able to meet the demands of large saturation intensity and narrow absorption bands have been inefficient, pulsed, expensive, and of limited area, making uniform illumination difficult. New Nd+3,Cr+3 co-doped solid-state laser materials that can be grown in large diameters [Laser Focus, 1989], and which boast both relatively low saturation intensities and broad absorption spectra, which make them easier to pump, and which have the high thermal conductivity of crystals (relative to glasses), such as GSGG [Krupke, et. al., 1986], promise to change this by making possible the use of pump sources that were not previously feasible. One of those pump sources may be nuclear-driven fluorescers. Nuclear-driven fluorescers (NDFs) utilize charged particles from nuclear reactions, such as ,; fission, to excite fluorescer gases. While limited to charged particle power den·sities of <10 kW/cm3, nuclear excitation can efficiently and uniformly excite large volumes without additional power conversion hardware [Prelas, Boody; Miley & Kunze, 1988]. NDFs are inherently high average power long pulse steady-state devices. However, the deleterious effects of nuclear radiation, as well as low peak fluorescence intensities, have made NDFs impractical for pumping solid-state lasers. We have developed a new geometry for NDFs that solves the radiation problem by shielding the laser from radiation and using a lightpipe to transport the fluorescence around the shield. This geometry also substantially concentrates the fluorescence which, combined with the lower saturation intensity requirements, brings the required pumping power density into the range of NDFs.

Material surface modification by pulsed ion beam

Abstract: A new technique utilizing a high-power-density pulsed ion beam for modification of material surfaces is presented. The power density of the pulsed ion beam ranges between 104 and 107 wcm−2, the kinetic energy is 1 to 5 KeV, the deposition energy is of the order of 1 to 10Jcm−2 and the pulsed duration is about 60μsec. The post-treatment samples were analysed using Auger electron spectroscopy, scanning electron microscopy, X-ray diffractometry, and Vicker's microhardness tester. It is found that the concentration of the injected particles has a Gaussian distribution. The thermal zone induced by the fast heating-cooling process forms a white-bright layer, indicating that there are new carbides and nitrides produced in the surface layer, which increases the microhardness of the surface.

Seawater batteries for low power, long term applications

Abstract: Two different seawater cells for long term discharge (years) have been developed. One type is for deep-sea use, whereas the other cell is intended for use close to the surface where biofouling is a major problem. The energy density of a complete system with DC/DC power converter and secondary battery in a pressure-resistant casing is above 600 Wh/kg for both cells. The seawater environment and cell development are discussed. Common properties for these seawater batteries are: infinite shelf life when dry; environmentally safe (neither poisonous or flammable): only the electronics design is pressure dependent; low lifetime cost (only the anodes are expendable); high energy density: and low power density. >