Showing papers on "Energy conversion efficiency published in 1992"

85% efficiency for cw frequency doubling from 1.08 to 0.54 μm

Abstract: Conversion efficiency of 85% has been achieved in cw second-harmonic generation from 1.08 to 0.54 μm with a potassium titanyl phosphate crystal inside an external ring cavity. An absolute comparison between the experimental data and a simple theory is made and shows good agreement.

35% efficient nonconcentrating novel silicon solar cell

Abstract: An energy conversion efficiency of 35% was obtained at 1‐sun, air mass 1.5 for a novel silicon cell. The critical feature of the cell structure is the inclusion of local defect layers near a p‐n junction. The local defect layers were proven to hold the key to achieving the exceptionally high efficiency of the novel cell fabricated via noncomplex processing.

Diode-pumped self-frequency-doubled neodymium yttrium aluminum borate (NYAB) laser

Abstract: Over 50 mW of the fundamental-mode 531-nm laser output was obtained with approximately 4% optical-to-optical conversion efficiency from a self-frequency-doubling NYAB crystal when pumped with two 1-W diode lasers. The prospect of higher conversion efficiency is discussed. >

Efficient LaF 3 :Nd 3+ -based vacuum-ultraviolet laser at 172 nm

Abstract: Vacuum-ultraviolet (VUV) laser radiation at 172 nm has been obtained from a solid-state LaF3:Nd3+-based laser pumped by a pulsed-discharge molecular F2 laser at 157 nm. The maximum slope efficiency of the solid-state laser described in this experiment was 21% (14% conversion efficiency), and the maximum output energy at 172 nm was 0.4 mJ for a nonoptimized optical cavity. This finding introduces serious prospects for realizing versions of active-medium-plus-source tunable VUV laser devices.

Resonant nonlinear laser beam converter

Abstract: Multiple step nonlinear conversion apparatus for optical frequencies which make use of resonant enhancement to increase net conversion efficiency. In one embodiment, two nonlinear converters are disposed in a single buildup cavity. In a second embodiment, two buildup cavities are provided, with one nonlinear element in each. In the single cavity configuration of the invention, the pump laser output is resonated in a buildup cavity and a first nonlinear element is used to generate the second harmonic. The second harmonic is resonated to enhance the doubling efficiency. A second nonlinear element mixes the pump beam and the second harmonic to produce an output beam at a linear combination of the two resonated frequencies. The conversion efficiency of the mixing is enhanced by the buildup factors at both the pump frequency and the second harmonic frequency. The buildup factors produced by the resonator enhance both the doubling and the mixing steps simultaneously. This is a versatile nonlinear conversion approach which applies both to frequency tripling and frequency quadrupling. In a special case, the third harmonic of the pump frequency is produced if the phase matching condition is adjusted to mix the laser frequency and the second harmonic. In a further special case, the fourth harmonic is generated when the phase matching is adjusted to mix the second harmonic beam with itself.

One joule output from a diode-array-pumped Nd:YAG laser with side-pumped rod geometry

Abstract: Output of 1.25 J per pulse (1.064 mu m) with an absolute optical efficiency of 28% and corresponding electrical efficiency of 10% was demonstrated in a diode-array-pumped Nd:YAG laser using a side-pumped rod geometry in a master-oscillator/power-amplifier configuration. In Q-switched operation, an output of 0.75 J in a 17-ns pulse was obtained. The fundamental laser output was frequency doubled in KTP with 60% conversion efficiency to obtain 0.45 J in a 16-ns pulse at 532 nm. The output beam had high spatial quality with pointing stability better than 40 mu rad and a shot-to-shot pulse energy fluctuation >

Evaluation of pulse voltage generators

Abstract: In this paper, the electrical characteristics of the positive pulsed corona in a wire-cylinder type reactor are investigated. The injected energy and charge into the discharging volume per pulse and per unit length of corona emitting wire are adopted to evaluate the power source, electric circuits, and the corona wire. The discharging current lasts from several hundred nanoseconds to a few microseconds. The current, power peak values, and the injected energy and charge per pulse per unit length of emitting wire can reach up to 60 A/m, 5 MW/m, 480 mJ/m, and 8 /spl mu/C/m, respectively. The energy conversion efficiency related to the output energy from the pulse forming capacitor and the energy delivered to the discharging volume can reach up to 90%. All results are obtained at room temperature and in air. >

Harmonic conversion of large-aperture 1.05-microm laser beams for inertial-confinement fusion research.

Abstract: To provide high-energy, high-power beams at short wavelengths for inertial-confinement fusion experiments, we routinely convert the 1.05-microm output of the Nova, Nd:phosphate-glass, laser system to its second- or third-harmonic wavelength. We describe the design and performance of the 3 x 3 arrays of potassium dihydrogen phosphate crystal plates used for type-II-type-II phase-matched harmonic conversion of the Nova 0.74-m diameter beams. We also describe an alternate type-I-type-II phasematching configuration that improves third-harmonic conversion efficiency. These arrays provide conversion of a Nova beam of up to 75% to the second harmonic and of up to 70% to the third harmonic.

Tunable, Coherent Vacuum Ultraviolet Radiation for Photoionization Mass Spectrometry

Abstract: Coherent vacuum ultraviolet radiation between 118 and 129 nm (10.5 and 9.6 eV) is generated by third-harmonic conversion of radiation between 355 and 390 nm. The conversion efficiency of a single negatively dispersive rare gas (xenon or krypton) is compared to the efficiency of a mixture of a negatively dispersive gas with a positively dispersive gas (argon). The rare-gas mixtures are found to give significantly higher third-harmonic conversion efficiencies. They also have much narrower wavelength tuning ranges than the single gases. Optimum gas pressures, mixing ratios, and conversion efficiencies are tabulated at selected wavelengths. The photoionization characteristics of compounds that exhibit little or no parent ion abundance with conventional 70-eV electron impact ionization are evaluated with tunable vacuum ultraviolet radiation. n-Alkanes, alkenes, aldehydes, amines, carboxylic acids, ethers, and ketones are ionized without significant fragmentation by using wavelengths close to the ionization thresholds. Alcohols and esters, however, fragment extensively, even at the ionization threshold.

Multi-megawatt superradiant emissions from coumarin-doped sol-gel derived silica

Abstract: Fluorescence and lasing properties of coumarindoped silica samples prepared by sol-gel process were investigated. Superradiant emissions at peak power as high as 7MW were measured at around 535 nm when the silica samples were excited by a XeF laser. The energy of the superradiant pulse was 89 mJ, corresponding to a conversion efficiency of 36.6%.

High-repetition-rate femtosecond pulse generation in the blue.

Abstract: We report the generation of high-repetition-rate femtosecond pulses in the blue by intracavity doubling of a mode-locked Ti:sapphire laser using β-BaB2O4. To reduce the pulse-broadening effect of group-velocity mismatch, an extremely thin β-BaB2O4 crystal is used. By pumping the Ti:sapphire laser with 4.4 W of power from an Ar+ laser, as much as 230 mW of 430-nm light is produced at a 72-MHz repetition rate and a 89-fs pulse width. This represents an effective conversion efficiency of ~75% from the typical infrared output to the second harmonic. Pulse widths as short as 54 fs are achieved for the blue output.

Blue-light generation by frequency doubling of a laser diode in a periodically domain-inverted LiTaO/sub 3/ waveguide

Abstract: The authors report quasi-phase matched second-harmonic generation by frequency doubling of a laser diode in LiTaO/sub 3/ having a first-order periodically domain-inverted region and proton-exchanged channel waveguide. A deep domain-inverted region and a low-loss channel waveguide with strong confinement are formed by using proton-exchange and quick heat treatment techniques. Utilizing this structure, a high normalized conversion efficiency of 157%/W is obtained with a Ti:Al/sub 2/O/sub 3/ laser. Using a temperature-controlled laser diode and AR coating on the input and output facet of the waveguide, the laser diode maintains single-mode oscillation without any mode hopping. Consequently, 1.1 mW of blue light is obtained at a wavelength of 436.5 nm. >

Influence of surface texturization on the light trapping and spectral response of silicon solar cells

Abstract: A quantitative model that explains the spectral response, internal quantum efficiency, total short-circuit current, open-circuit voltage, and efficiency of high-efficiency solar cells with textured front surface and Lambertian back-surface reflectors is presented. A comparison of the textured cell characteristics is made with those of planar cells, and the separate roles of the front surface reflection coefficient and internal quantum efficiency in enhancing the short-circuit current have been investigated. It is shown that, in the case of large diffusion lengths, almost all the contribution to the increase of spectral response on texturization is due to the reduced reflection coefficient whereas, for small diffusion lengths, there is a significant increase in internal quantum efficiency on texturization, especially in the region of higher wavelengths. However, there is a small decrease in open-circuit voltage for large diffusion lengths, whereas no significant change is observed for small diffusion lengths on texturization. Nevertheless, there is a net gain in power conversion efficiency which is larger for smaller diffusion lengths. >

Nonlinear optical wavelength converters with feedback

Abstract: An optical frequency conversion apparatus includes at least one resonator (10) having an optical path defined by a plurality of mirrors (M1, M2). A nonlinear conversion medium (10a) is disposed within the optical path of the resonator, the nonlinear conversion medium receiving optical radiation at a first frequency and outputting optical radiation at a second frequency that is a multiple of the first frequency. One of the plurality of mirrors is an input mirror (M1) for coupling into the resonator a pulse of radiation having the first frequency, and one of the mirrors is an output mirror (M2) for out-coupling a pulse of radiation having a frequency that is a multiple of the first frequency. The input mirror has a predetermined reflectivity that is selected to cause the pulse of radiation to have an intensity sufficient to maximize, with respect to the pulse of radiation, a conversion efficiency of the nonlinear medium, without exceeding a damage threshold for the nonlinear conversion medium or for any of the plurality of mirrors. The teaching of the invention is also applied to third, fourth, and higher order harmonic generators, to optical parametric oscillators and amplifiers, and to optical mixers. Also disclosed is an intra-cavity wavefront distortion corrected second harmonic generator that compensates for heating of a nonlinear conversion medium at high average powers.

Conversion loss of a YBa2Cu3O7 grain boundary mixer at 20 GHz

Abstract: We have measured the conversion gain of a YBa2Cu3O7 annealed grain boundary microbridge mixer by operating the device as a lower side‐band down‐converter from an 18.5 GHz radio frequency to a 1.5 GHz intermediate frequency under the action of a 20.0 GHz local oscillator. We have found the conversion gain to be relatively independent of bias up to a current density which marks the onset of the flux flow resistance. Above the onset of flux flow resistance, the gain decreased dramatically. A maximum conversion gain of −8±4 dB was measured at 25 K. The mixer was operated with a local oscillator power of only −60 dBm. The results demonstrate that high Tc superconductor mixers are capable of delivering comparable conversion gains to Schottky diode mixers while requiring substantially lower power local oscillators.

High-energy, high-efficiency second-harmonic generation of 1064-nm radiation in KTP.

Abstract: An energy conversion efficiency of 80% for second-harmonic generation of 532-nm radiation from 1064-nm radiation has been achieved with a single KTP crystal and a commerical injection-seeded Q-switched Nd:YAG laser A second-harmonic output of 720 mJ was generated with 900 mJ of incident 1064-nm radiation at 10 Hz

High conversion efficiency of second-harmonic generation in step quantum wells

Abstract: Second‐harmonic generation due to intersubband transitions in GaAs/AlxGa1−xAs step quantum well structures has been studied with a tunable TEA CO2 laser. The maximum value of χ(2)(2ω) is found to be ∼9×10−7 m/V. Using a multipass or ‘‘waveguide’’ structure, a conversion efficiency of more than 3×10−4 has been obtained.

Generation of 312 nm, femtosecond pulses using a poled copolymer film

Abstract: A 2.5- mu m-thick corona-poled copolymer film was used to double approximately 13-fs-long, 50-nJ-energy, 625-nm-wavelength pulses at a 8-kHz repetition rate. The large effective d coefficient results in a relatively high conversion efficiency for such a thin film. A maximum efficiency of 0.13% has been measured. Long-term stable operation was obtained with efficiencies of 0.025% at the damage threshold of approximately 160 GW/cm/sup 2/. The damage threshold is remarkably high for organic materials and was found to be peak intensity rather than average intensity dependent. >

Efficient harmonic generation with a broad-band laser

Abstract: Harmonic generation using a broadband input beam is studied theoretically and experimentally. Angular spectral dispersion is imposed on the input beam to improve the phase matching and thereby increase the conversion efficiency. The coupled amplitude equations are derived for a grating-dispersed input beam, and it is shown that, in the parameter range of interest, a simple theoretical model based on the intuitive concept of instantaneous frequency suffices to describe the nonlinear interaction. A laser having a frequency-chirped output with a 25-AA bandwidth is used to demonstrate the technique for third-harmonic generation in the small-signal regime. >

Blue light generation by frequency doubling of AlGaAs broad area amplifier emission

Abstract: The diffraction limited emission of a traveling wave single pass 600‐μm wide SQW GaAlAs amplifier injected by a Ti:Sapphire laser was frequency doubled in KNbO3 to generate 400 mW peak power 5 μs long pulses of 431 nm light. A maximum single pass frequency conversion efficiency of 6.3% was observed.

High efficiency microwave diode oscillators

Abstract: Data on the operation of very high efficiency microwave oscillators using AlAs/InGaAs quantum well injection transit (QWITT) diodes are presented. A DC-to-RF power conversion efficiency as high as 50% was achieved, which, to the authors' knowledge, is the highest efficiency reported for continuous wave (CW) operation of a two terminal semiconductor device.

Energy conversion by photoelectrolysis of water: Determination of efficiency by in situ photocalorimetry

Abstract: By means of a power balance analysis for a water-splitting photoelectrolysis cell, relations have been derived for determining the energy conversion efficiency, with respect to absorbed monochromatic light, from photocalorimetric in situ measurements at the semiconductor photoanode. It is shown that a quantity readily obtainable from the potential dependence of the heat-monitoring signal represents the upper limit of the energy efficiency attainable with a given photoanode

Observation of enhanced thermal lensing due to near-Gaussian pump energy deposition in a laser-diode side-pumped Nd:YAG laser

Abstract: The authors report operation of a laser-diode side-pumped Nd:YAG laser with a novel pumping geometry that ensures efficient conversion of pump energy into the TEM/sub 00/ mode. Significant enhancement of thermally induced lensing due to the near-Gaussian energy deposition profile of the pump radiation was observed. An induced lens of approximately 3.2-m focal length was measured at average incident pump powers of only 3.2 W (corresponding to a 0.6 W heat load). >