Showing papers on "Power density published in 1970"

Theory of intracavity optical second-harmonic generation

Abstract: An analysis of optical second-harmonic generation internal to the laser cavity is presented. It is shown that the maximum second-harmonic power generated in this way is equal to the maximum fundamental power available from the laser. Further, it is found that there exists a value of nonlinearity that optimally couples the harmonic out for all power levels of the laser. The magnitude of the nonlinearity required for optimum coupling is shown to be proportional to the linear losses at the fundamental and inversely proportional to the saturation parameter for the laser transition. For the YAlG:Nd laser at 1.06 μ using Ba 2 NaNb 5 O 15 as the nonlinear material, the required crystal length for optimum coupling is given by l\min{c}\max{2}(cm)\simeq 2.7 \times 10^{2}L/f where L is the linear round-trip loss and f is the ratio of the fundamental power density in the nonlinear crystal to that in the laser medium. For low-loss cavities, optimum coupling can thus be achieved for crystal lengths of 1 cm or less. The use of a mirror or mirrors within the cavity, reflecting at the harmonic, is considered as a means to couple out the total harmonic in one direction. Considerations of temperature stability and the finite oscillating linewidth of the laser are shown to favor a configuration with a single harmonic mirror located on the same surface as the fundamental mirror.

Gas Breakdown with 10.6‐μ‐Wavelength CO2 Laser Radiation

Abstract: The gas‐breakdown threshold or the minimum power density required to ionize a gas with 10.6‐μ‐wave‐length radiation has been examined using the radiation of a Q‐switched CO2 laser. The studies show that the focused beam cannot initiate the breakdown process for intensities as high as 109 W/cm2. If an initial low degree of ionization is provided by an external source, the subsequent growth of the breakdown is in agreement with a cascade model as evidenced by the experimentally determined gas pressure and laser‐radiation frequency dependence.

RF Sputtered Aluminum Oxide Films on Silicon

Abstract: The physical and electrical properties of aluminum oxide films deposited on silicon by rf sputtering from an alumina target in an argon atmosphere were investigated as a function of sputtering power density in the range from 0.5 to 3 W/cm2. The deposition rates ranged from 20 to 80 Aa/min. The density, index of refraction, and dielectric constant of the films increased while the etch rate decreased with increasing power density. The surface charge at the aluminum oxide‐silicon interface was typically larger than 1012 e/cm2. This charge increased with increasing sputtering power density and could be reduced to by annealing. The films exhibited trapping instabilities at room temperature but no polarization was observed under bias‐temperature stress. The characteristics of composite layers of thermally grown silicon dioxide and sputtered aluminum oxide layers on silicon were also investigated and found to exhibit low surface charge densities, no hysteresis, and a "contact potential" as well as charge stored at the interface between the two insulators.

Measurements of the noise spectral power density of photosensitive materials at high spatial frequencies.

Abstract: A new method of measuring the scattered light to determine the noise spectral power density is described. The technique is shown to be useful at the high spatial frequencies used in holography, beyond the range of the former methods of noise power measurement. Measurements of the grain noise of several photographic emulsions used for holography are presented; they are consistent with a model of emulsions characterized by a transmission correlation length. The measured correlation length of several of the emulsions fit experimentally observed spatial frequency responses. Data on noise power of several other photosensitive materials suitable for holography are also presented.

Atmospheric Attenuation of Microwave Power

Abstract: Large earth satellite power stations have been proposed to convert solar energy to microwave energy and to transmit it to earth receiving stations. What wavelength region and how large a power density can he transmitted from the satellite power sta-to earth without significant interaction and subsequent loss of energy to the earth’s atmosphere is discussed. In the wavelength region of 3–30 cm, three attenuation mechanisms are investigated: nonlinear phenomena of the ionosphere, gaseous attenuation of water vapor and oxygen, and hydrameteor attenuation of clouds and rain. It is concluded that for power densities of 0.01 w/cm2, the optimum wavelength region for transmission of microwave power through the earth’s atmosphere is the 10 cm region.

Microwave acoustic surface wave limiter and method of fabrication

Abstract: Power density curves of acoustic surface waves generated in piezoelectric substrate members by sum and difference electromagnetic input signals have been found to peak at discrete distances from the input transducer. An effective microwave mixer is provided by positioning an appropriately tuned output transducer on the substrate member at a point coinciding with the desired sum or difference acoustic signal power peak.

Microwave power density meter

Abstract: A power density meter for monitoring the energy density of an electromagnetic field, having a first radiant field and a stationary field, in the near-zone region of an electromagnetic apparatus. The power density meter comprises an antenna arrangement having a conical horn, a stub, an output portion and an input portion. The electromagnetic wave energy of the radiant field is received by the horn and stub. The input portion is located in front of the horn and comprises a sheet of lossy material sandwiched between a pair of thin sheets of plastic. When the lossy material is brought into the stationary field, a current is induced into the material which is representative of the electromagnetic energy of the stationary field. The current established in the lossy material generates a second radiant field which is additive to the first radiant field of the electromagnetic wave energy. The output portion includes a cryster detector receiving the combined electromagnetic energy from the first and second radiant fields. A circuit is provided for coupling the detector to a meter so that a signal representative of the value of the power density in the near-zone region may be displayed on the meter.

On the Temperature Distribution in Graphite Matrix Hollow Fuel Compacts

Abstract: With the view to gaining basic information to serve in reactor design and to permit better evaluation of fuel properties, the temperature distribution in graphite matrix hollow fuels containing Th is discussed on the basis of information obtained from equations expressing the temperature as a function of power density, fuel properties and cooling conditions. The relations found as a result among these factors indicate that high power density can be expected by adopting a combination of high thermal conductivity (<0.06 cal/cm·sec·°C) optimized ratio between inner and outer diameters of hollow fuel (about 1:3), and high heat transfer coefficient of gap between fuel and sheath (by reducing the gap width to less than 0.2 mm). The temperature rise in the blanket is found to be insignificant.

High Power Density Fuel Cell.

Abstract: : An exploratory development program continuing the investigation of high power density hydrogen-oxygen fuel cell technology was conducted. An evaporatively cooled four-cell power section was designed, fabricated, and successfully tested at a steady-state power density exceeding 1500 watts per square foot, about 10 times the power density of conventional space fuel cell. The High Power Density (HPD) power section fabricated and tested consisted of a stack of four hydrogen/oxygen, alkaline electrolyte, low-temperature, matrix fuel cells of 0.14 sq ft active area. Externally fed wick evaporator units between cells removed heat by evaporation of water at controlled pressure and temperature. Product water from the fuel cell reaction was vented to the atmosphere. Over 300 cell-hours have now been accumulated at high power density. (Author)

Interaction of Microwave Radiation with a Polar Gas under Conditions of Power Saturation

Abstract: The propagation of microwave radiation through a gas‐phase dielectric under conditions of power saturation is considered. It is shown that the nonuniform polarization gives rise to additional modes of electromagnetic oscillation. The amplitudes of the induced electric field are estimated and shown to be small. The results of the calculation substantiate that Harrington's method of averaging the power distribution in determining the power density distinction function φwg is correct for application to microwave spectroscopy.

Testing Batteries for Vehicular Applications II . Tests on Some Commercially Available Energy Batteries

Abstract: Using a versatile test facility previously described, a number of commercially available Pb-acid batteries were tested. Typical test results are presented, especially those most meaningful to vehicular applications. It is shown that at varying power discharges the energy capabilities are additive. By this means, performance, range, and capability of batteries under varying duty cycles can be ascertained. Power density vs. energy density curves are obtained almost by inspection from constant power discharges. Voltage-current characteristics, both for charge and discharge, at varying capacity levels are presented. It is shown that Pb-acid batteries can be charged rapidly to 80-85% of their capacity before battery voltage rises rapidly.

Fuel cell–battery power sources

Abstract: Fuel cells now being developed are not replacing batteries, but are assisting secondary batteries in fuel cell—battery hybrid configurations to power a wide range of portable communications and surveillance equipment. The secondary battery provides the required power density and the instantly available power while the fuel cell efficiently converts a primary fuel to electrical power at a continuous steady rate to provide extremely high energy densities over extended missions.

Theory of Intracavity Optical Second-Harmonic

Abstract: Abslract-An analysis of optical second-harmonic generation internal to the laser cavity is presented. It is shown that the maximum second-harmonic power generated in this way is equal to the maximum fundamental power available from the laser. Further, it is found that there exists a value of nonlinearity that optimally couples the harmonic out for 211 power levels of the laser. The magnitude of the nonlinearity required for optimum coupling is shown to be proportional to the linear losses at the fundamental and inversely proportional to the saturation parameter for the laser transition. For the YA1G:Nd laser at 1.06 p using BagNaNb50ts as the nonlinear material, the required crystal length for optimum coupling is given by 1z(cm)c= 2.7 X lOeL/f where L is the linear round-trip loss and f is the ratio of the fundamental power density in the nonlinear crystal to that in the laser medium. For low-loss cavities, optimum coupling can thus be achieved for crystal lengths of 1 cm or less. The use of a mirror or mirrors within the cavity, reflecting at the harmonic, is considered as a means to couple out the total harmonic in one direction. Considerations of temperature stability and the finite oscillating linewidth of the laser are shown to favor a configuration with a single harmonic mirror located on the same surface as the fundamental mirror.