摘要:

Monte Carlo calculations of keV electron‐energy‐loss distributions have been performed using a simple model of the generalized oscillator strength density to simulate inelastic collisions. The model, which rests partly on the use of empirical data (primarily the atomic mean ionization potential) expresses the generalized oscillator strength density as a sum of terms ( j) of the form [ fj&dgr;(W−Wj),Q<Wj;fj&dgr;(W−Q),Q>Wj] whereWis energy transfer,fjandWj( j=1,2,3,...) are a sequence of oscillator strengths and resonance energies, respectively, andQ=ℏ2q2/2m, where ℏqis the momentum transfer andmthe electron mass. Comparison is made with experimental results reported for 2an transmission through Al, and 7.3‐keV internal conversion electrons transmitted through surface layers of Fe.

ISSN:0021-8979    

DOI:10.1063/1.334709

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We have studied the dipole‐allowednd3/2‐nf5/2and the dipole‐forbiddennd3/2‐ng7/2transitions of sodium in the presence of thermal ions forn=15–17. Although the cross sections for the relevant ion–Rydberg atom collisons are too small to influence the observed transitions, these microwave resonance measurements indicate that there is a remarkable influence of even very low densities, 105cm−3, of ions on the atoms. For instance, thed‐gtransition can be easily driven with a single photon, and thed‐fandd‐gtransitions are shifted and broadened. Furthermore, the thermal sodium ions destroy the interference fringes obtained with the Ramsey method of separated oscillatory fields. Although these results are incompatible with reasonable estimates of ion‐atom collision cross sections, they may be explained quantitatively in terms of the time‐averaged charge of the ions.

ISSN:0021-8979    

DOI:10.1063/1.334710

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Experiments are described in which low‐pressure mercury, mercury‐argon, and mercury‐krypton discharges were irradiated with a dye laser pulse at 405 nm, thus exciting mercury atoms from the metastable 63P0level to the 73S1level. The 73S1level decays radiatively to the 63Plevels. By recording the time dependence of the 63P1level density at the 254‐nm fluorescence signal, the effective radiative lifetime of this level was determined. These measurements were performed for a wide range of mercury vapor densities. From the effective radiative lifetime and the 63P1level density, the 254‐nm output can be calculated. Reasonable agreement is found for two discharges of which the 254‐nm output had been measured directly.

ISSN:0021-8979    

DOI:10.1063/1.334711

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A general formulation is given for electromagnetic pulses which remain localized in a multidimensional space, and which propagate at the speed of light without dispersing (focus wave modes). It is shown that such modes necessarily have infinite electromagnetic energy in the source‐free, three‐dimensional space. Finite‐energy focus wave modes cannot exist without sources. A set of complete focus wave modes with Hermite–Gaussian transverse variation is derived. The relation of focus wave modes to the solutions of the paraxial wave equation is established.

ISSN:0021-8979    

DOI:10.1063/1.334712

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A spinning superconducting sphere generates a magnetic field (the London field) while excluding external magnetic fields from its interior (the Meissner effect), so that a torque on the sphere results if there are magnetic or superconducting materials nearby. We calculate the torque on such a sphere inside a concentric, infinitely long superconducting cylinder. We also calculate the torque on such a sphere inside a concentric, spherical superconducting shell in which there is a single circular hole.

ISSN:0021-8979    

DOI:10.1063/1.334713

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Double scattering lidar events involving long cylindrical particles are discussed. The scatterers are allowed to be randomly oriented and the geometry required in the scattering solution is described in detail. The geometry is general, made to be applicable to any type of particle for which the single scattering matrix is provided, relative to the main axis of the scatterer. Results of the double scattering calculations are presented for the penetration of the lidar light into clouds of different optical depth &tgr; (&tgr;≤0.5).

ISSN:0021-8979    

DOI:10.1063/1.334714

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Rubidium atomic frequency standards have been found to display a strong frequency dependence on the microwave power density or field intensity. It is, therefore, desirable to have simple and easily applied techniques for measuring not only the field strength but also the field distribution within the clock’s microwave cavity. A technique which makes use of adiabatic rapid passage (ARP) to measure field strengths in Rb clock cavities is described and demonstrated. Measurements using this technique are found to agree with field strengths extracted using standard microwave procedures. The ARP technique is particularly valuable in cavities where standard microwave measurements cannot be made.

ISSN:0021-8979    

DOI:10.1063/1.334715

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Experiments are described on a plasma cathode with biased grids to prevent entry of ions into the electron extraction gap. The cathode has potential applications to the generation of high‐current pulsed electron beams. Operation at 20 A/cm2is theoretically possible. The source combines the low average power consumption of a plasma cathode with many of the attractive features of thermionic cathodes, such as space‐charge‐limited extractor gap electron flow, fast turn‐on, and no diode closure. Initial experiments are reported at the 2 A/cm2level for pulse lengths to 160 &mgr;s.

ISSN:0021-8979    

DOI:10.1063/1.335479

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Using a high‐energy single‐pulse DF laser, a multiple‐pulse effect (MPE) occurs for aluminum alloys in air. It requires an incident fluence well above the plasma threshold fluenceeT. After a number of exposures, the thermally coupled fluence is almost three times the plasma‐enhanced value seen for single pulses aboveeT. The absorptance beloweTat 3.8 &mgr;m increases by a factor of 5. We now find that the MPE depends on the presence of O2. New experimental data were taken well aboveeTin air at low pressures and in gas mixtures at 1 atm with varied O2content. Plasmas were present but the MPE was not for low O2. The normal single‐pulse enhancement was absent without O2.

ISSN:0021-8979    

DOI:10.1063/1.334716

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

TE‐TM mode conversion caused by magnetic linear birefringence (MLB) has been studied in liquid‐phase‐epitaxially grown (BiGdLu)3(FeGa)5O12films. The films were grown on Gd3Ga5O12substrates of which the face normal is tilted from the (111) axis by the angle &thgr;c. The LPE growth on the substrate with &thgr;c≠0 made the magnetization of the film tilt from the film normal, and this enabled the mode converter to work without any applied external field. The theory developed to describe the function of the mode converter agreed well with the experimental results. The MLB coefficient is about −9 rad/cm at a wavelength &lgr;=1.15 &mgr;m. The Bi substitution is effective to enhance the MLB effect. A role of the MLB mode converter to realize a simple and compact waveguide optical isolator is discussed.

ISSN:0021-8979    

DOI:10.1063/1.334717

出版商:AIP    

年代:1985

数据来源: AIP