Showing papers on "Energy conversion efficiency published in 1990"

24% efficient silicon solar cells

Abstract: Significant improvements in silicon solar cell performance are reported using an improved high‐efficiency silicon solar cell structure. This structure overcomes deficiencies in an earlier structure by locally diffusing boron into contact areas at the rear of the cells. Terrestrial energy conversion efficiencies up to 24% are reported for silicon cells for the first time. Air Mass 0 efficiencies lie in the 20–21% range, the first silicon cells to exceed 20% efficiency under space illumination.

Optical-damage-resistant LiNbO(3):Zn crystal.

Abstract: Zinc doping is shown to reduce the photorefraction in LiNbO3:Zn. The damage-resistant crystal LiNbO3:Zn has demonstrated a conversion efficiency of approximately 50% for frequency doubling of 1.06-μm radiation. The dependence of optical characteristics on the ZnO concentration in the melt reveals a sharp change of the optical properties at the threshold concentration of 4–6 mol % Zn. The optical and nonlinear-optical data of LiNbO3:Zn are similar to those of LiNbO3:Mg, but the former shows better optical performance.

Conversion of Light into Electricity with Trinuclear Ruthenium Complexes Adsorbed on Textured TiO2 Films

Abstract: A series of CN-bridged trinuclear Ru complexes of the general structure [RuL2(μ-(CN)Ru(CN)L2′)2] where L is 2,2′-bipyridine-4,4′-dicarboxylic acid and L′ is 2,2′-bipyridine (1)2,2′-bipyridine-4,4′-dicarboxylic acid (2), 4,4′-dimethyl-2,2′-bipyridine (3), 4,4′-diphenyl-2,2′-bipyridine (4), 1,10-phenanthroline (5), and bathophenanthrolinedisulfonic acid (6) have been synthesized, and their spectral and electrochemical properties investigated. The two carboxylic functions on the 2,2′-bipyridine ligand L serve as interlocking groups through which the dye is attached at the surface of TiO2 films having a specific surface texture. The role of these interlocking groups is to provide strong electronic coupling between the π* orbital of the 2,2′-bipyridine and the 3d-wave-function manifold of the conduction band of the TiO2, allowing the charge injection to proceed at quantum yields close to 100 %. The charge injection and recombination dynamics have been studied with colloidal TiO2, using laser photolysis technique in conjunction with time-resolved optical spectroscopy. Photocurrent action spectra obtained from photo-electrochemical experiments with these trinuclear complexes cover a very broad range in the visible, making them attractive candidates for solar light harvesting. Monochromatic incident photon-to-current conversion efficiencies are strikingly high exceeding 80% in some cases. Performance characteristics of regenerative cells operating with these trinuclear complexes and ethanolic triiodide/iodide redox electrolyte have been investigated. Optimal results were obtained with complex 1 which gave a fill factor of 75 % and a power conversion efficiency of 11.3% at 520 nm.

Broadly tunable vacuum-ultraviolet radiation source employing resonant enhanced sum–difference frequency mixing in krypton

Abstract: Vacuum-ultraviolet (VUV) generation by resonant third-order sum–difference frequency conversion (wVUV = 2wR − wT) in krypton has been investigated. The frequency wR (λR = 212.55 nm) was resonant with the Kr two-photon transition 4p–5p[1/2, 0]. By tuning wT in the range λT = 220–860 nm it was possible to generate wVUV in the wavelength range λVUV = 200–120 nm. The conversion efficiency was enhanced in the range 121–123 nm by phase matching with a normally dispersive buffer gas (Ar); under the best phase-matched conditions employed, VUV output powers at the Lyman-α wavelength of the order of 1 kW were inferred from the estimated VUV pulse energy. This source was used to measure high-lying members of the Mg principal series near 162 nm. High resolution and excellent sensitivity of detection, when a thermionic diode detector was used, have been demonstrated.

Generation of 41 mW of blue radiation by frequency doubling of a GaAlAs diode laser

Abstract: A monolithic ring resonator of KNbO3 was used for efficient frequency doubling of a 856 nm GaAlAs diode laser. A special electronic servo technique was devised to lock the diode laser frequency to the KNbO3 cavity so that stable generation of blue output was obtained. With 105 mW of incident near‐infrared power, 41 mW of 428 nm radiation were produced. The conversion efficiency from electrical input power into the diode laser to blue output was ∼10%.

Over 35% efficient GaAs/GaSb stacked concentrator cell assemblies for terrestrial applications

Abstract: It has been previously noted that GaSb infrared-sensitive cells can be stacked behind transparent GaAs cells to boost solar cell energy conversion efficiencies to well over 30% for space and terrestrial applications. Verified spectral response and current versus voltage data for both GaAs and GaSb cells along with Sandia National Laboratories clear-day solar spectral data for Albuquerque, US, are used to calculate the stack performance for various spring, summer, fall, and winter days in Albuquerque at both 25 degrees C and at projected cell normal operating temperatures (NOT). It is found that the stack annual average energy conversion efficiency is 35.6% at 25 degrees C and 32.5% at NOT. During the year, the tandem stack efficiency at 25 degrees C varies by a small amount, from a low of 35.3% to a high of 35.8%. >

Efficient photoelectrochemical solar cells from electrolyte modification

Abstract: PHOTOELECTROCHEMICAL solar cells (PECs)1–3 have shown energy conversion efficiencies approaching 13% in sunlight4, and up to 15% in simulated insolation5. Of these, only those incorporating n-cadmium chalcogenide electrodes have been demonstrated to be conducive to thin film6 or in situ storage systems7. Previous studies of photoelectrochemical current and voltage limitation2,3,5,8,9 have focused on modification of the semiconductor electrode. Here we take the alternative approach by demonstrating that energy conversion can be improved by prevention of electrode surface modification and by systematic modification of the electrolyte. Electrolyte modification entails investigations of the primary photo-oxidized species, the nature of the counter ion, the distribution of species in solution, and related competing reactions. Optimization of the distribution of species and addition of cyanide to n-CdSe/([KFe(CN)6]2−/3−)aq PECs enhances the available voltage and the ease of charge transfer, and suppresses related decomposition products. The resultant PEC achieves an open-circuit potential of 1.2 V, an efficiency of 16.4%—the highest for any wide-band-gap (1.7 eV) solar cell (solid state or photoelectrochemical)—and a 100-fold improvement in photocurrent lifetime. Each of these represents a step towards realization of a viable PEC.

Detuning characteristics and conversion efficiency of nearly degenerate four-wave mixing in a 1.5- mu m traveling-wave semiconductor laser amplifier

Abstract: The optical nonlinearity in a semiconductor laser gain medium is investigated through copropagating nearly degenerate four-wave mixing (NDFWM) in a 1.5- mu m InGaAsP traveling-wave laser amplifier (TWA). The FWM signal output powers vary symmetrically with the sign of probe detuning with respect to the pump frequency, while the pump and probe output powers vary asymmetrically. The NDFWM conversion efficiency from the probe input to the FWM signal output is a maximum of 8.3 dB around zero detuning and has positive gain in the range of +or-6 GHz. This demonstrates highly efficient nonlinear interaction due to both large optical gain and large third-order susceptibility. The NDFWM efficiency is also investigated in connection with the TWA gain saturation characteristics and is found to be a maximum for operation around the saturation intensity of the TWA. >

Laser surgery system

Abstract: A multi-wavelength surgical laser apparatus of improved construction employs a fluid-filled stimulated Raman scattering cell in an optical feedback path of a pump laser having a power in a range suitable for surgery, and drives the Raman cell at a high repetition rate in a manner to produce a laser output at a substantially shifted wavelength at a power commensurate with that of the pump laser. In a preferred system, the relative proportions of pump light and Raman scattered light are varied to achieve a desired cutting or coagulating action. Preferably, the pump laser is operated at a pulse repetition rate above five hundred Hz. The fluid Raman medium is pumped across the optical axis of the cell. The flow system effectively doubles the Raman conversion efficiency and permits high power output while lowering the Raman lasing threshold. Systems include a fiber for conducting output light to a surgical probe, and a variable output coupler to vary the relative amounts of pump and Stokes radiation coupled into the fiber. Light generated at visible wavelengths by Stokes processes in the Raman cell provides auxiliary beam for targeting or observation purposes.

Method and apparatus for converting low temperature heat to electric power

Abstract: A method and apparatus for implementing a thermodynamic cycle which may be used to convert low temperature heat to electric power.

Design and fabrication of highly efficient fan-out elements

Abstract: This paper reports the calculation and fabrication of periodic phase structures for fan-out elements with a theoretical conversion efficiency close to 100% and perfect uniformity. We have measured an efficiency of 92% for a smooth kinoform structure fabricated in photoresist by laser beam writing lithography.

Power conversion apparatus with harmonic filtration

Abstract: A power conversion apparatus capable of eliminating inexpedient higher harmonic components from its output, without lowering the conversion efficiency. The apparatus includes a first power converter for converting an input power from a power supply into an output power; a detector for detecting an output current and an output voltage of the first power converter; a high harmonic detector for detecting a higher harmonic component on a basis of the output current and the output voltage, and for producing current reference signal corresponding to the detected higher harmonic component; and a second power converter for producing an inverse of the detected higher harmonic component according to the current reference signal, and combining the produced inverse of the higher harmonic component with the output current of the first power converter such that the higher harmonic component in the output current of the first power converter are cancelled by the inverse of the higher harmonic component.

Stretching of slow positron pulses generated with an electron linac

Abstract: A facility for generating a high intensity slow positron beam using an electron linear accelerator has been constructed. A conversion efficiency of 6×10−7 slow positrons per incident electron has been obtained for 75 MeV electrons. Storage and stretching of pulsed slow positrons have been successfully carried out with a Penning trap.

Conversion of laser light into soft x rays. Part I: Dimensional analysis

Abstract: The conversion of laser light into soft x rays by irradiation of a high‐Z material is theoretically investigated for open, planar geometry. The material may be subdivided into a hot, low‐density conversion layer, optically thin for the x rays, and a dense, optically thick reemission zone. The two layers are coupled through radiation only. Dimensional analysis yields asymptotic expressions for the x‐ray conversion efficiency and the reemission coefficient and hence for the total converted flux from the target.

Doping Effect on the Two-layer Organic Solar Cell

Abstract: Doping effect on an organic solar cell composed of two-layer thin pigment films of metal-free phthalocyanine (H2Pc) and perylene tetracarboxylic derivative (Me-PTC) was investigated. When H2 or NH3 was doped to the Me-PTC film during vacuum deposition, the photocurrent density drastically increased and the power conversion efficiency of the cell reached about 1% even under 75 mW cm−2 white light.

Thermal X-Ray Emission from Ion-Beam-Heated Matter

Abstract: The conversion of ion beam energy into thermal x-ray radiation by means of stretched cylindrical plasma volumes is studied by analytic modeling and numerical simulation. The analysis is restricted to one-dimensional radiation hydrodynamics. Scaling relations for different materials are derived. Due to equation-of-state properties, high-Z material turns out superior for achieving high conversion efficiency. The paper provides practical answers for thermal x-ray generation with intense heavy ion beams. Deposition powers in the order of 1016 W/g are required for applications to ion beam inertial confinement fusion.

An excimer-pumped beta -BaB/sub 2/O/sub 4/ optical parametric oscillator tunable from 354 nm to 2.370 mu m

Abstract: A pulsed singly resonant optical parametric oscillator (OPO) has been constructed which can provide tunable coherent radiation over the entire wavelength range extending from 354 nm in the near ultraviolet, throughout the visible, to 2.370 mu m in the near infrared using a single beta -BaB/sub 2/O/sub 4/ crystal. The oscillator is pumped at 308 nm by a pulsed narrow band injection-seeded XeCl excimer laser in a near-field pumping configuration, and energy conversion efficiencies (optical-to-optical) in excess of 10% have been obtained in a 12-nm-long crystal across the OPO tuning range. The requirements placed upon the spectral and spatial coherence of the pump laser for optimum OPO operation are discussed. Experimental results on several oscillator parameters, including tuning range, oscillation threshold, energy conversion efficiency, and spatial and temporal characteristics, are presented. >

Conversion of laser light into soft x rays. Part II: Numerical results

Abstract: The conversion of laser light into soft x rays during interaction of intense laser light with a planar gold target was investigated numerically with the help of the multi code [Comput. Phys. Commun. 49, 475 (1988)]. It solves one‐dimensional hydrodynamics including flux‐limited electron heat conduction, multigroup radiation diffusion, and steady‐state nonlocal thermodynamic equilibrium radiation physics. The influence of various parameters such as the laser intensity, wavelength, and pulse duration on the conversion efficiency of laser light into x rays was studied. Particular emphasis was placed on comparing the numerical results with the model presented in the preceding paper (Part I) [Phys. Fluids B 2, 199 (1990)]. According to this model the radiating plasma can be divided into a conversion layer and a reemission zone. Its essential features are confirmed by the numerical results.

Stimulated Raman shifting of the Nd:YAG fourth harmonic (266 nm) in H/sub 2/, HD, and D/sub 2/

Abstract: The dependence of the first Stokes stimulated Raman conversion efficiency of fourth-harmonic radiation from a Nd:YAG laser at 266 nm has been studied for the isotopic species H/sub 2/, HD, and D/sub 2/ as a function of gas pressure and laser energy using a low numerical aperture ( approximately 4.5*10/sup -3/) pumping geometry. While the laser energy threshold for first Stokes conversion is seen to vary significantly between the species it has been found that photon conversion efficiencies of at least 50% can be achieved for all of them for laser pump energies at 266 nm >

Ti:sapphire laser pumped by a frequency-doubled diode-pumped Nd:YLF laser.

Abstract: We report on the operation of a tunable all-solid-state (holosteric) laser system consisting of a tunable Ti:sapphire laser pumped by a frequency-doubled diode-laser-pumped Nd:YLF laser. With a 1-W pump diode, the Nd:YLF laser has been frequency-modulation mode locked and Q switched at 1.047 μm. This produces a pulse envelope of 75-nsec duration with 45 μJ of energy in 21-psec pulses at a 360-MHz repetition rate. This output was frequency doubled in 90° phase-matched MgO:LiNbO3 with a 47% energy conversion efficiency. The Ti:sapphire cavity was a three-mirror astigmatically compensated arrangement. The threshold absorbed pump energy was 3.9 μJ, with an output energy of 1.3 μJ at 10.8-μJ absorbed pump power. The tuning range was 746–838 nm and was limited by the mirror reflectivities.

Theory and conceptual design of a high-power highly efficient magnicon at 10 and 20 GHz

Abstract: It is shown that magnicons can be scaled up to high frequency (X-band and above) at high power and efficiency. Magnicons have an advantage over other slow wave devices in that the structure sizes are comparable to or larger than a wavelength, so RF breakdown should be less of a problem. However, they require higher voltage. The magnicon has the promise of considerably enhancing the technology of efficient high-power high-frequency RF sources. >

Efficient optical amplifier using a low-concentration erbium-doped fiber

Abstract: A gain coefficient of 3.8 dB/mW was achieved for an erbium-doped fiber amplifier pumped by a 1.48 mu m laser diode. The main reasons for the improvement are high NA (0.23) and low concentration (43 p.p.m.). Pump-to-signal energy conversion efficiency was 18% at 3 dB gain compression. A decrease in saturation power with increasing erbium concentration was also demonstrated. In high-concentration fiber, fluorescence at 0.98 mu m due to cooperative upconversion was detected. These results indicate that several kilometers of distributed fiber amplifier with high gain and high output saturation power could be possible, because the absorption coefficient at 1.48 mu m is still two orders higher than the background loss in the 43 p.p.m. fiber. >

Quantum well laser utilizing an inversion layer

Abstract: A quantum well laser exhibiting near ideal switching characteristics, high power conversion efficiency and, moreover, capable of utilizing the advantageous characteristics of a double heterostructure optoelectronic switch comprises a quantum well region disposed between carrier confinement regions. In particular, the interface between the qunatum well regioin and a confinement region is adapted to the formation of an inversion layer.

High average power edge emitting laser diode arrays on silicon microchannel coolers

Abstract: We have demonstrated high average power output devices in both one‐dimensional (1‐D) and two‐dimensional (2‐D) arrays of laser diodes using efficient edge emitting cleaved bars and silicon microchannel coolers. These packages are based on the rack and stack architecture. For the 1‐D array a cw optical power output of 22.2 W was obtained with 20% electrical to optical conversion efficiency. For the 2‐D array an average optical power density of greater than 100 W/cm2 was obtained at an efficiency of 25%.

Improved contact metallization for high efficiency EFG polycrystalline silicon solar cells

Abstract: Improvements in the performance of polycrystalline silicon solar cells based on a novel, laser-patterned contact process are described. Small lots of cells having an average conversion efficiency of 14+%, with several cells approaching 15%, are reported for cells of 45 cm/sup 2/ area. The high-efficiency contact design is based on YAG laser patterning of the silicon nitride antireflection (AR) coating. The Cu metallization is done using light-induced plating, with the cell providing the driving voltage for the plating process. The Cu electrodeposits into the laser-defined windows in the AR coating for reduced contact area, after which it bridges on top of the Ar coating to form a continuous finger pattern. The higher cell conversion efficiency is attributed to reduced shadow loss, higher junction quality, and reduced metal-semiconductor interfacial area. >

Frequency conversion of broad-bandwidth laser light

Abstract: The efficacy of angular spectral dispersion by a grating as a means of improving the frequency conversion efficiency of broad-bandwidth laser light is investigated. It is shown that when the bandwidth arises from phase modulation, the zero-bandwidth conversion efficiency can be recovered in this way if the modulation is sufficiently slow, and that the frequency bandwidth is multiplied by the same factor as the frequency. When the bandwidth is due to amplitude modulation, the method is less effective. The theory is illustrated by calculations of third-harmonic generation in KDP. >