摘要:

Here, proceeding from a previous study, the deformation problem of a viscose fluid is analyzed under simplified conditions as regards the physical model. This viscose fluid is used as the light control organ in the light valve method of large‐screen television projection. By using simple approximate relationship, the important properties, such as dynamic behavior, frequency response, stability behavior, and resolution limit of the control layer and their dependence on material and system parameter are discussed in detail. The theoretical knowledge obtained from this analysis agrees to a large extent with the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.334343

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The absorption coefficient of two high‐purityn‐InSb samples is measured in the 10–40 cm−1range using Fourier transform spectroscopy. The absorption coefficient spectrum is presented for both samples at 4.2 K. It is also shown for the lower resistance sample cooled to 2.2 K and heated by dc bias to elevated electron gas temperatures of 7.5 and 17.9 K. ac Drude theory gives rather poor agreement with experiment at 2.2 and 4.2 K but does much better when the sample electron gas is heated. In contrast, a simple quantum mechanical theory of absorption based on inverse Bremsstrahlung yields promising agreement at the lower temperatures although its applicability is questionable. The non‐Drudian absorption is shown to have a favorable effect on the performance of InSb hot‐electron bolometers.

ISSN:0021-8979    

DOI:10.1063/1.334344

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A statistical model, the local plasma approximation, is considered for the calculation of the logarithmic mean excitation energy for stopping power of chemically bound particles by taking into consideration chemical bonding. This statistical model is applied to molecular hydrogen and leads to results that suggest a value for the logarithmic mean excitation energy of molecular hydrogen that is larger than the accepted experimental and theoretical values.

ISSN:0021-8979    

DOI:10.1063/1.334345

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Under transient excitation the energy transmitted by an antenna of finite size to a faraway receiver can decrease much more slowly than the usualR−2. Instead, by a suitable choice of excitation, this quantity can decrease as slowly as one wishes, under the physical restriction that the total energy radiated by the antenna is finite. Such cases of slow decrease are referred to as electromagnetic missiles. Another way of stating the result is that the product of the following two quantities can approach zero as slowly as one wishes: (1) the energy transmitted per unit area of receiver, and (2) the total area of the receiver. Examples are constructed when either one, but not both, of these quantities remains finite at infinite distance.

ISSN:0021-8979    

DOI:10.1063/1.335465

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A procedure for using digital image processing techniques to measure the spatial correlation functions of composite heterogeneous materials is presented. Methods for eliminating undesirable biases and warping in digitized photographs are discussed. Fourier transform methods and array processor techniques for calculating the spatial correlation functions are treated. By introducing a minimal set of lattice‐commensurate triangles, a method of sorting and storing the values of three‐point correlation functions in a compact one‐dimensional array is developed. Examples are presented at each stage of the analysis using synthetic photographs of cross sections of a model random material (the penetrable sphere model) for which the analytical form of the spatial correlations functions is known. Although results depend somewhat on magnification and on relative volume fraction, it is found that photographs digitized with 512×512 pixels generally have sufficiently good statistics for most practical purposes. To illustrate the use of the correlation functions, bounds on conductivity for the penetrable sphere model are calculated with a general numerical scheme developed for treating the singular three‐dimensional integrals which must be evaluated.

ISSN:0021-8979    

DOI:10.1063/1.334346

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An experimental study of electrostatic electron lenses as a function of geometrical and electrical parameters is described. The lenses are of the symmetrical three‐electrode unipotential type. The parameters are the thickness of the center electrode and the interelectrode spacing, both relative to the center electrode aperture diameter, and the ratio of lens voltage to cathode voltage. The lens properties are characterized in terms of the focal length and focal distance, and the spherical and chromatic aberrations of these quantities. In general, the principal surfaces of a lens are not plane, and the aberrations of focal length and focal distance are not the same. Expressions are derived relating the focal length and focal distance aberrations to the spherical and chromatic imaging aberration coefficientsCsandCc, and the magnification aberrations. The advantages of formulating the lens properties in terms of focal length and focal distance and their aberrations, and the usefulness of the data presented here, are illustrated with several examples.

ISSN:0021-8979    

DOI:10.1063/1.334347

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Interfering Gaussian laser beams are sometimes used to photochemically etch gratings into materials; the gratings which result are nonuniform since the groove depth varies over the grating cross section. The grating growth can be monitored in real time by observing the diffraction of the writing beams into their various orders. In order to relate the maximum groove depth to the observed diffraction efficiency, the grating nonuniformity must be accounted for. We present a short calculation which does this. The results are checked with measurements on actual gratings and good agreement is obtained. The results can help to interpret previously published measurements.

ISSN:0021-8979    

DOI:10.1063/1.334348

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Geometrical considerations are important with respect to the stability and efficiency of avalanche electric discharge lasers. Parameters such as the electrode contours and the distribution of preionization electrons affect excitation rates through the relative values of the local electric field, local depletion of initial species, and through the response of the discharge circuitry to spatially dependent conditions within the plasma. Constriction of the discharge and subsequent impedance mismatch of the discharge to the pulse forming line result from these spatial nonuniformities. In this paper geometrical effects in the mercury bromide electric discharge laser are examined by comparing the results from a multidimensional discharge and kinetics model with experimental observations. The code models electron and heavy particle kinetics and laser intensity in time and one spatial dimension: parallel to the electrodes and perpendicular to the optical axis. Quantities whose spatial dependence is perpendicular to this dimension, such as the contours of the electrodes, are accounted for through their impact on the local electric field. HgBr laser efficiency and spatial characteristics are examined as a function of stored electrical energy, the impedance of the pulse‐forming circuitry, electrode contours, and profile of the preionization electron density. Parasitic discharges within the gas, but exterior to the optical cavity, are examined as a mechanism through which the magnitude of the preionization density can effect laser efficiency.

ISSN:0021-8979    

DOI:10.1063/1.334349

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new thermal analysis of a catastrophic mirror damage in laser diodes is presented in the present paper. Three‐dimensional heat spreading and temperature dependence of a thermal conductivity is taken into account in the model. Both an active layer heating and a nonradiative recombination of carriers generated by absorbed radiation in an active area close to a facet mirror are considered as heat sources. The model is strictly correct for times ranging from 6.2 to 500 nsec for a standard stripe laser diode, i.e., for currents not higher than 4.5 A and not lower than 0.8 A. The analytical solution of the thermal conduction equation gives a dependence of a catastrophic‐degradation time, i.e., a permissible length of current pulses from a point of view of the catastrophic mirror damage, on the amplitude of the pulses for the standard stripe laser diode.

ISSN:0021-8979    

DOI:10.1063/1.334350

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Parameters relevant to the operation of an electron‐beam initiated atomic iodine laser, which would lase on the transition 52P1/2(I*)→52P3/2(I), have been measured by pulse radiolysis. Kinetic data for the parent compound quenching of I* were obtained by variation of the parent compound pressure at constant buffer gas pressure and observing I* decay rates versus time. Deactivation rates for perfluoroalkyl iodides were found to be much lower than for the corresponding alkyl iodides. Values obtained (in cm3molec−1s−1) are as follows: CH3I, (2.0±0.1)×10−13; C2H5I, (5.0±0.3)×10−13; CF3I, (8.8±0.3)×10−16; C2F5I, (9.7±1.0)×10−15;n‐C3F7I, (2.5±0.2)×10−15;i‐C3F7I, (1.7±0.1)×10−15;n‐C4F9I, (1.8±0.1)×10−14. The extent of population inversion was investigated by measuring initial excited state and ground state atomic iodine concentrations, which gives the branching ratio [I*]/[I]. Values obtained are as follows: CH3I, 2.7; CF3I, 3.8; C2F5I, 2.7;i‐C3F7I, 3.2;n‐C4F9I, 1.8. Comparing both branching ratios and lifetimes, it is seen that CF3I is the most promising candidate for an electron beam initiated atomic iodine laser.

ISSN:0021-8979    

DOI:10.1063/1.334351

出版商:AIP    

年代:1985

数据来源: AIP