摘要:

The propagation of an annular intense relativistic electron beam inside a cylindrical drift tube is affected by many factors such as external magnetic field, drift tube geometry, the beam self electric and magnetic fields, etc. It is shown, experimentally and theoretically, that the deleterious influence of the self‐fields on the electron flow can be reduced when part of the beam return current is allowed to flow on a grounded conductor that is inserted coaxially within the beam. The improvement manifested itself by reducing the axial magnetic field needed to confine the electron beam or alternately by lowering the electron transverse velocities.

ISSN:0021-8979    

DOI:10.1063/1.362976

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A two‐dimensional treatment suitable both for perpendicular (Pockels readout optical modulators, etc.) and for parallel (image amplifiers, etc.) photorefractive devices is presented. A partial differential equation of the third order, valid for both families of devices, is set up and solved analytically for the relevant initial and boundary conditions in the full time domain. The results are illustrated in a few examples showing the relative significance of bulk and surface charges, and some new features of the solution for the perpendicular configuration. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362978

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Mid‐infrared lead‐chalcogenide diode lasers can be operated at convenient operation temperatures using short current pulses and thus allow a wide range of potential applications. Our goal was to optimize the spectral characteristics of pulsed lasers by well‐defined current pulse shaping. The high‐frequency current tuning coefficient has been evaluated experimentally for this reason. Different tuning mechanisms are discussed by use of a model calculation. The qualitative features can be explained by assuming a separate temperature for the carriers that form a thermodynamic system of their own and are heated by the current. The tuning characteristics can be explained due to carrier concentration variations induced by free‐carrier absorption. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362925

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Lamp‐pumped laser performance of Nd3+‐doped strontium fluorapatite, Sr5(PO4)3F or S‐FAP, has been characterized and compared with that of Nd3+‐doped yttrium aluminum garnet (YAG) at both 1.06 and 1.3 &mgr;m. Nd3+:S‐FAP was found to exhibit lower thresholds and lower slope efficiencies than Nd3+:YAG. The former is attributed to the higher emission cross section, and the latter to lower Nd3+concentration in S‐FAP. The 1.3 &mgr;m lasing of Nd3+:S‐FAP is of particular interest because of its high emission cross section (2.4×10−19cm2).Q‐switched and dual‐wavelength lasing operation were also demonstrated in Nd3+:S‐FAP. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362926

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The polarization properties of valence intersubband transitions inp‐type doped Si0.75Ge0.25/Si multiple quantum wells are investigated using Fourier infrared absorption spectra. It is found that TE and TM polarized light beams both can excite valence intersubband transitions in SiGe/Si multiple quantum wells. Meanwhile, a strong dichroism is also observed for HH1→HH2transitions because the splitting peaks between TE and TM absorption have different activity unders‐ andp‐polarized states. However, the strong mixing of light‐ and heavy‐hole states in split‐off state SO1weakens the dichroism of HH1→SO1transitions. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362927

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a fast algorithm for calculations of the temperature distributions induced by the energy beam in the three‐dimensional deposits of arbitrary shape. It combines analytical approximations, numerical fast Fourier transform, and the multigrid technique. The accuracy of the method is demonstrated with problems that can be solved analytically. The behavior of the center temperature in laser‐deposited spots and stripes of different shapes and sizes is studied. The results can explain explosive growth in laser‐induced deposition and instabilities in laser direct writing, and provide a tool for a quantitative analysis of energy beam microprocessing. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362928

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Computational modeling is a key tool for studying collisional plasma discharges, including capacitive, inductive, and dc discharges. This work compares electron‐neutral collision rates for a particle‐in‐cell code, a Monte Carlo code, a convected scheme Boltzmann code, and a spherical harmonic expansion Boltzmann code. In addition, comparisons with swarm experiments are presented where available. The comparison is performed over a range of reduced fields,E/N, appropriate to ac plasma display panels. The background gas is neon, with a simplified set of representative reactions. Ion and space charge effects are neglected. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362929

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report measurements of the energies and angular distributions of positive ions in an inductively coupled argon plasma in a Gaseous Electronics Conference Reference Cell. Use of two separate ion detectors allowed measurement of ion energies and fluxes as a function of position as well as ion angular distributions on the discharge centerline. The inductive drive on our system produced high plasma densities (up to 1012/cm3electron densities) and relatively stable plasma potentials. As a result, ion energy distributions typically consisted of a single feature well separated from zero energy. Mean ion energy was independent of rf power and varied inversely with pressure, decreasing from 29 to 12 eV as pressure increased from 2.4 to 50 mTorr. The half‐widths of the ion angular distributions in these experiments varied from 5° to 9°, or equivalently, the transverse temperatures varied from 0.18 to 0.29 eV with the distributions broadening as either pressure or rf power was increased. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362977

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Optical emission and absorption spectroscopy and double Langmuir probe diagnostics have been applied to measure the plasma parameters of an expanding magnetized hydrogen plasma jet. The rotational temperature of the excited state H2(d2&Pgr;u) has been determined by analyzing the intensity distribution of the spectral lines of the Fulcher‐&agr; system of H2. The gas temperature in the plasma, which is twice the value of the rotational temperature is equal to &bartil; 520 K. Several clear indications of presence of the ‘‘hot’’ electrons have been observed in the plasma: (1) Langmuir probe measurements (Te&bartil;1.4 eV), (2) appearance of the Fulcher‐&agr; system of H2(excitation potential &Dgr;E=13.87 eV), (3) low rotational temperature (T*rot&bartil;260 K) of the excited H2(d3&Pgr;u) molecules, (4) local excitation in the plasma of Ar I(&Dgr;E=15.45 eV), and Ar II(&Dgr;E=19.68 eV) spectral lines, (5) local excitation in the plasma of He I(&Dgr;E=23.07 eV and &Dgr;E=24.04 eV) spectral lines. Optical actinometry has been applied to measure the absolute density of hydrogen atoms and hydrogen dissociation degree in the plasma. The measured absolute density of hydrogen atoms are in the (1–1.4)×1020m−3range, and the corresponding dissociation degree of the hydrogen plasma is in the range of 8%–13%. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362930

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A set of electron‐molecule cross sections in CF4has been derived using the solution of the Boltzmann equation under the hydrodynamic regime. The set is evaluated by fitting the calculated swarm parameters to the experimental data. The obtained set is consistent with measured swarm parameters (drift velocity, transversal diffusion coefficient, ionization, and attachment coefficients), not only in pure gas but also in argon–CF4mixtures as well with the data available. Information about cross sections (form and magnitude) coming from direct determination has also been respected, even though it is scarce. In mixtures, the electron swarm parameters drastically change even when a small amount of CF4is added, showing a negative differential conductivity in the drift velocity. This phenomenon is studied in detail. Furthermore, the introduction of the superelastic collisions in the calculations is also justified. In the gas under study, due to the importance of the vibrational cross sections at low energy, the anisotropy of the electron energy distribution function is so high that it must be taken into account in the method used for solution of the Boltzmann equation. The validity of the set of cross sections (including elastic momentum transfer, vibrations, dissociation, ionization, and attachment) has been tested by comparing calculated and measured swarm data not used in the unfolding procedure. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362931

出版商:AIP    

年代:1996

数据来源: AIP