摘要:

A simplified charge control type of analysis is made of the response of photoconducting imaging devices with a floating electrode. The change of electrode potential with discharge of the device is found to have an importance not previously recognized. The results are relevant for a variety of electrostatic photographic devices and show the dependence of the performance on certain details of the image development process.The floating electrode limits the gain during exposure to light to one charge pair per quantum absorbed. For the Vidicon TV camera picture tube, a detailed study of the process of reading the stored information demonstrates that net gain exceeding unity can be achieved. The upper limit to the gain is the ratio of the time for the scanning beam to traverse a picture element to the transit time of a free carrier through the layer. This conclusion holds when the time required to trap a free carrier exceeds its recombination lifetime. None of the gain‐bandwidth relations yet deduced for photoconductors is applicable to this case. Earlier studies which led to a maximum gain of approximately unity for the Vidicon assumed fast trapping of free carriers.For the Vidicon, the conditions for gains greater than unity with full frame storage and small lag are developed, including the characteristics of the scanning beam and of the trapping and recombination centers. Suitable targets with only one free carrier should have a low sensitivity photoconductor with a significant density of slow trapping states. Discussion of the similarity between the performance of a homogeneous target with one free carrier and annpnstructure shows that the slow trapping states in the uniform layer play the role of the donors and acceptors in the junction device.

ISSN:0021-8979    

DOI:10.1063/1.1729097

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Masers exhibit interesting transient behavior that cannot be completely understood on the basis of the rate equations. The use of the rate equations in most transient analyses is usually justified on a more or less intuitive basis and the implied assumptions are not always clear. In this paper, the macroscopic maser rate equations are derived systematically from the Boltzmann equation for the density matrix of the atomic systems and Maxwell's equations for the radiation fields. When the coherence linewidth (T2−1) of the atomic systems is much larger than the cavity linewidth and the natural linewidth (T1−1) of the atomic emission, and with a WKB approximation, in the lowest order of approximation one obtains the two widely used, coupled first‐order nonlinear rate equations of Statz and deMars. On the other hand, if the cavity linewidth is much larger than the atomic linewidths (T1−1andT2−1), one can use the so‐called ``reaction‐field principle'' of Anderson and obtain, again, two coupled first‐order rate equations; however, only one of the equations is nonlinear. The ranges of validity of both approaches are discussed in some detail.

ISSN:0021-8979    

DOI:10.1063/1.1729098

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The propagation of finite amplitude electromagnetic waves in a gyromagnetic medium is discussed. It is shown, using the method of characteristics, that in the quasistatic or low frequency limit a wave propagating parallel to the external dc magnetic field distorts continuously until a discontinuity or electromagnetic shock wave appears in the wave profile. When higher‐order effects are taken into account, the shock front is found to have a finite width which is reached by a balance between the nonlinear wave‐steepening torque term and the wave‐broadening loss term. The calculated shock‐front width is found to be independent of crystalline anisotropy and exchange and magnetoelastic effects. The theoretical results are compared with numerical calculations and the possibility of using electromagnetic shock waves in pulse sharpening networks and microwave devices is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1729099

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A detailed analysis of space‐charge instabilities in diodes is presented. The oscillation when the input current exceeds the ``limiting input current'' (from an earlier analysis for a short circuited diode with a zero temperature stream) persists with the addition of a diode resistance, or with a two‐velocity input or a Maxwellian velocity distribution input, or with streams of finite diameter. The time‐averaged value of the minimum potential is nearly zero, as in the classical solution; however, the time‐averaged minimum position and transmitted current differ considerably from the classical values. The recovery of the stable state is by a jump rather than gradually as in the classical solution. A small‐signal prediction of time growth of all first‐order variables (potential, current, velocity) at the point of limiting is given. An energy argument using the zero‐order variables is presented showing the onset of instability. Experiments agreed with some parts of the analysis but did not show oscillations with amplitudes as large as expected.

ISSN:0021-8979    

DOI:10.1063/1.1729100

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The pressure shift of both the coherent and the incoherent emission of GaAs junction lasers has been measured at about 200°K. The peak of the spontaneous emission shifts by +1.09×10−5eV/atm, which is in agreement with the pressure coefficient of the band gap in GaAs determined by experiments based on the change of resistance under pressure. The shift of the coherent modes is much smaller, namely, +2.96×10−6eV/atm. The effect of the compressibility on the latter shift is shown to be negligible. It is concluded from considerations of a simple model that the shift of the coherent radiation is primarily due to a change of the dielectric constant with pressure.

ISSN:0021-8979    

DOI:10.1063/1.1729101

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Measurements have been made of the electrical conductivities of gaseous mixtures formed by the addition of small fractions of cesium vapor to nitrogen, helium, neon, or argon. The mixtures were maintained near thermal equilibrium at temperatures in the 1500°–2000°K range and a total pressure of one atmosphere. The cesium vapor pressures ranged over two decades, from 0.1 to 10 Torr.The apparatus consists, in essence, of two heated zones connected by a slow flow. The first zone is a low‐temperature (200°–400°C) oven where the body‐gas flow picks up the cesium vapor. The second zone is a small electrically heated furnace (1250°–1850°C) containing a diode test section.The principal measurements taken were the seeding temperature, furnace temperature, and voltages and currents in the test section.The results exhibit variations with temperature, seeding pressure, and gas species that correlate reasonably well with simple theory and values for electron collision frequencies and cross sections taken from the literature.

ISSN:0021-8979    

DOI:10.1063/1.1729102

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Small differences between the emission and absorption spectra of three‐level maser centers can have a pronounced effect on maser operation. This paper considers the effects of a Stokes shift, the simplest and most probable difference. If there is a Stokes shift which is large compared to the linewidth, the operation of the maser will be essentially four level. If there is a small Stokes shift (some fraction of the linewidth) the operation will still be three level, but the Stokes shift will significantly affect the operation of the maser. The principal effects will be a shift of the maser line from the peak in the fluorescent emission line (away from the absorption peak) and a reduction in the upper level population required to reach the threshold of oscillation.The evidence is not conclusive as to whether there is a Stokes shift in the rubyR1line, but if there is a shift it is at most a small fraction of the fluorescent linewidth at room temperature. Shifts of the ruby maser line to the red have been observed by D'Haenens and Asawa and have been attributed to large temperature changes. It is likely that the temperature shift, while important, will not explain the shift which has been observed. Gires and Mayer have found the lower state population of an operating ruby maser to be approximately 75% of the unexcited population rather than approximately 50% and have suggested a Stokes shift as a possible cause of the reduction in the upper state population at threshold. This paper considers the effect of such a small Stokes shift on the operation of an otherwise ideal three‐level maser.

ISSN:0021-8979    

DOI:10.1063/1.1729103

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The disk model of an electron beam, generalized to allow a distribution of dc velocities, leads to a set of equations that include space charge and accurately describe the nonlinear behavior of a multivelocity electron beam in a drift region. Difference equations are obtained which are suitable for solution on a digital computer. Excellent agreement is obtained at small‐signal levels with linearized theory. Available for the first time as a result of the validity of the present analysis for nonlinear conditions are: (1) harmonic behavior at small‐signal levels and (2) fundamental and harmonic behavior at large‐signal levels.

ISSN:0021-8979    

DOI:10.1063/1.1729104

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The nonlinear disk electron analysis in Part I is applied to a practical example. Two changes are imposed on the analysis to decrease the computer running time. Electron trajectories and the first three components of current are calculated for a beam with a rectangular velocity distribution that is simulated by eight dc velocity classes. Excellent agreement is obtained with a linear theory for small values of initial density modulation. Periodic variation of the space‐charge parameter leads to the equivalent of scalloped beam amplification in a multivelocity beam.A linear force‐taper correction is derived and its stabilizing effect is shown. Its use is suggested for improving the accuracy of monovelocity disk electron calculations.The interpretation of space‐charge wave decay in multivelocity electron beams as spatial Landau damping of the fast wave is questioned. It is suggested that damping is due to multidimensional effects not taken into account by present linear and nonlinear one‐dimensional theories.

ISSN:0021-8979    

DOI:10.1063/1.1729105

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The ultrasonic‐diffraction effect was utilized as a shutter to gate and amplitude modulate the output of a ruby optical maser (laser) by regulating the optical feedback within the Fabry‐Perot interferometer. In addition, an oscillation resembling limit cycle operation was induced in the ruby laser by an ultrasonic‐progressive wave that periodically changed the optical path length between the interferometer reflectors by varying the refractive index.

ISSN:0021-8979    

DOI:10.1063/1.1729106

出版商:AIP    

年代:1963

数据来源: AIP