摘要:

In this article, we present the characteristics of the &Dgr;F=±1, &Dgr;mF=±1, &pgr; microwave transitions which appear in the response of cesium beam resonators operating with U‐shaped waveguide Ramsey cavities bent in the plane of theHfield. Such resonances are due to the presence in the cavity of microwave magnetic induction perpendicular to the static field direction. It is shown that the &pgr; resonance feature is derived from a pure two‐level atomic system interacting with four spatially separated oscillating fields. Good agreement is found between experimental data and theoretical predictions when we take into account the actual transverse microwave field profile in the cavity obtained with tridimensional electromagnetic field computations. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.360652

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Electro‐optic properties of thin‐film materials grown on opaque substrates are determined utilizing the principles of reflection differential ellipsometry. The scheme of the measurement involves the detection of the field‐induced phase shift in a probing light beam reflected from thin‐film samples. To quantitatively determine the field‐induced indices change or birefringence and the field‐induced strain it is essential to model the differential ellipsometric process in the stratified structure. The modeling reveals that the field‐induced changes of the ordinary and the extraordinary indices contribute to the measured phase shift with different incident‐angle dependences. The field‐induced strain gives yet another unique incident‐angle distribution. By means of an incident‐angle‐varying technique, therefore, the field‐induced changes of ordinary index and extraordinary index in a thin‐film material may be determined separately. Detailed descriptions of the measuring technique and the modeling work are presented. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360587

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A theoretical and numerical investigation of the effects of azimuthal and radial spreads of canonical momentum on an electron beam focused by a magnetic lens in the presence of space‐charge forces is presented. The particles are inserted with an initial Gaussian distribution in the transverse space and in the momentum coordinates or with a uniform initial current distribution. The particle trajectory equation is derived for parameters of an arbitrary applied fields configuration with cylindrical symmetry, and a nonvanishing initial canonical momentum. In the absence of an initial momentum spread particles launched above a critical radial distance from the axis exhibit aphase‐spacetearingeffect in the electron distribution. The inclusion of initial canonical momentum spread in the model allows for skewed trajectories with strong centrifugal force which prevents the appearance and overshadows the effect of strong space‐charge forces near the axis, which are responsible for the phase‐space tearing effect. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360647

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Numerical simulations of quantum tunneling with time‐dependent barriers show that there is a resonance, with a marked increase in the tunneling current. For square barriers the resonance occurs when the tunneling particles absorb modulation quanta and the length of the barrier is a multiple of one‐half de Broglie wavelengths. The resonance has a similar mechanism with triangular barriers. However, the relationship is more complex because the absorption and emission of modulation quanta takes place throughout the full length of the barrier, whereas this exchange only occurs at the ends of a square barrier. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360667

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Theoretical analysis of the output performance of a transverse discharge pumped neon Penning laser (585.3 nm) using a mixture of Ne/H2is described. The validity of the kinetic model is confirmed by comparing the results to the experimental discharge and laser performance. It is theoretically shown that the optimum mixing ratio of the Ne/H2mixture is 1:2.5, and the optimum operating pressure is about 56 Torr. The model also predicts that the intrinsic efficiency reaches a peak of 8.5×10−6at an excitation rate of 0.5 MW/cm3under the optimum mixing ratio and operating pressure conditions. At excitation rates in excess of 0.5 MW/cm3the laser output power is slowly increasing and then saturates due to electron collisional quenching of the upper laser level. The laser power extraction is increased by laser injection seeding in order to rapidly build up the lasing. The improved intrinsic efficiency is about two times higher than without the injection seeding. The improved specific laser output is 8 W/cm3, therefore, a discharge volume of 125 cm3will be able to generate the peak laser power reaching 1 kW. This power value is sufficient to obtain the same treatment effect as the gold vapor laser used in photodynamic therapy. Moreover, by fitting this model to the experimental results of the laser output energy with a Ne/D2mixture, it is shown that the Penning ionization rate constant of H2is larger than that of D2. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360677

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this article, we address the nonlinear properties of bulk acoustic waves in anisotropic solids. While ordinary driving waves are obtained by means of the quasiwave mode concept in the discussion on propagation problems, we focus our analysis on the driving wave satisfying the resonant condition which exhibits the characteristics of three‐dimensional spatial accumulation. Then a theory as the basis for solving nonlinear boundary value problems is developed. The novel analysis is presented for nonlinear reflection of bulk acoustic waves at a free surface of a generally anisotropic solid, which reveals that the surface may generate freely propagating second‐harmonic waves, and that the reflective second‐harmonic waves increase two dimensionally in the bulk. This technique can also be applied to wave reflection problems at other kinds of planar boundaries. Some numerical calculation is carried out for the case in an isotropic solid. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360615

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The kinetics of rise and decay of ground‐state atomic oxygen was investigated in a low‐pressure O2radio‐frequency discharge. The ground state of O was monitored using laser‐induced‐fluorescence spectroscopy. The discharge was operated in two modes: a continuous mode and a pulsed mode. Typical discharge settings are rf power of 100 W, a pressure of 10 Pa, and a gas flow of 10 sccm. Using a pulsed mode the behavior of the O density was determined in a pure O2discharge with no reaction products, and in a discharge during etching of organic polymers. Production and loss mechanisms for O in a pure O2discharge are discussed. For an O2discharge during etching of resist it is found that under the given experimental conditions atomic oxygen does not play a significant role in the chemical etch mechanisms involved. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360630

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A collisionless dynamic sheath model for multispecies plasmas has been derived for the application of plasma immersion ion implantation (PIII) processes with multispecies dopant gases. In this dynamic sheath model, a general form of an effective massM, which includes species compositions and ion masses, is used to determine the sheath expansion during the pulse. The total ion current, total implant dose, and the corresponding dose components for different species can also be determined with this effective mass. This offers a method for easily evaluating PIII processing and obtaining the correct implant doses for different species. A plasma simulation is used to compare this model. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360640

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Visible photoluminescence at room temperature has been observed in amorphous hydrogenated silicon particulates during their formation in a silane radio‐frequency plasma. Oxygen injection along with mass spectrometry measurements demonstrate that oxygen has no influence on the photoluminescence. The appearance of visible photoluminescence coincides with a particle agglomeration phase as shown by laser light scattering experiments, and electron microscopy shows silicon nanocrystals within these particulates. These observations of visible photoluminescence are consistent with the model of quantum confinement in the silicon nanocrystals. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360582

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A theoretical model for the microsecond‐conduction‐time plasma opening switch (POS) based on magnetohydrodynamics is presented. The operating processes are associated with the magnetic field transport in the switch. The concept of the freezing‐in of magnetic field in fluids is used to analyse the dynamics of this field in the plasma. One‐dimensional and two‐dimensional numerical simulations lead to the identification of two operating regimes, related to the Hall and the snowplow effects. The transition between these two regimes is determined by the plasma density. Scaling relations are developed from this model. In particular the electrical chargeQ, conducted by the POS during the conduction time, provides a useful tool for comparisons between theory and experiments; it is shown to be the essential parameter for the switch design. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360583

出版商:AIP    

年代:1995

数据来源: AIP