摘要:

The response of a magnetic gradiometer to various types of magnetic sources is analyzed. Both semiquantitative and quantitative methods for determining the noise immunity and the spatial sensitivity of the gradiometer are presented. A new class of magnetic gradiometers with unidirectional properties is introduced.

ISSN:0021-8979    

DOI:10.1063/1.327819

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Optical laser isotope separation (LIS) and chemical process concepts are developed that arise in the large‐scale application of LIS processes with continuous process streams. The discussion applies to one‐photon, two‐photon and multiphoton LIS and the separation of a multiple‐component mixture. It is partly based on a novel reaction chamber which provides throughout its volume a constant energy fluence or power density. Concepts discussed are the isotopic depletion, isotopic and process selectivity, isotopic abundances, abundance quotients &agr;* and &bgr;*, the photon utilization factor, and the material balance equations in the LIS plant. An expression is derived that gives the total process cost per unit separated product in terms of the isotopic selectivity, the isotopic depletion, and the natural abundance of the desired species. A total‐cost minimization is carried out which gives the optimum isotopic depletion of the process as a function of isotopic selectivity, photon cost parameters, and parameters characterizing the photochemical reaction and the feed costs. The expressions are applicable to ’’closed cycle’’ as well as ’’once through’’ feed processing. The results are used to estimate the cost per kg of heavy water as a function of laser efficiency and isotopic selectivity, for a formaldehyde‐based deuterium separation method.

ISSN:0021-8979    

DOI:10.1063/1.327820

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Using the Herman‐Skillman potentials and bound wave functions for each subshell of silver, we have computed the continuum wave functions, and subshell‐by‐subshell photoionization cross sections with photoelectron energies up to 10 keV. Applying a relationship between photoionization and electron impact ionization, we have obtained inverse mean free paths and stopping powers, again by subshell, for electrons penetrating through silver. The maximum electron energy considered is 100 keV. For the total photoionization cross section, comparison of our work with experiment shows excellent agreement for photon energies down to 100 eV, below which solid‐state effects should be included. Theoretical total inverse mean free paths, being strongly dominated by contributions from 4delectrons, are in good agreement with data around 1 keV, but about a factor of 2 larger at energies below 100eV. Our stopping power is in good agreement with other theoretical work above 400 eV and approaches the relativistic Bethe formula above 10 keV. Range is also computed and is in good agreement with other theoretical work.

ISSN:0021-8979    

DOI:10.1063/1.327821

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The generation of transition radiation resulting from the passage of relativistic charged particles through a periodic structure can produce intense and highly directional x rays. An optimization analysis accounting for material properties, multiple scattering, and statistical random errors in foil thicknesses is used to design an x‐ray emitter. The results demonstrate that transition radiation sources can be comparable in brightness to synchrotron emitters.

ISSN:0021-8979    

DOI:10.1063/1.327822

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Trajectories of particles emitted normally from a charged sphere into a constant magnetic field are examined. Calculations are made which separate such trajectories into two classes, those which return to the sphere and those which do not.

ISSN:0021-8979    

DOI:10.1063/1.327823

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We propose a new theoretical model for the light‐induced migration of charges which mediates the ’’photorefractive effect’’ (light‐induced refractive index change) in barium titanate and other crystals. We also present experimental results of various effects of this light‐induced charge migration in a single‐domain crystal of barium titanate, specifically, (1) energy transfer between two intersecting optical beams, (2) optical four‐wave mixing and optical‐beam phase conjugation, (3) erasure of spatial patterns of photorefractive index variations, and (4) photoconductivity. The theoretical model predicts the observed dependences of these effects on (1) beam intensities, directions, and polarizations, (2) crystal orientation, and (3) on an externally applied dc electric field. Time dependences of transients as well as steady‐state magnitudes are predicted. In this model, identical charges migrate by hopping between adjacent sites, with a hopping rate proportional to the total light intensity at the starting site. The net hopping rate varies with the local electric potential that is calculated self‐consistently from the charge migration pattern. In barium titanate the charges are positive with a density of (1.90.2) ×1016cm−3at 514 nm. The origin of the charges and sites is at present unknown. The hopping rate constant determined from optical beam interactions is used to predict the observed photoconductivity of 1.3×10−10cm &OHgr;−1 W−1at 514 nm.

ISSN:0021-8979    

DOI:10.1063/1.327824

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

High‐power (∼108W/l) discharges in metal‐doped Xe are modeled for typical metal atom densities of 1015–1017cm−3and Xe densities of ∼1020cm−3, and electron densities of 1014–1017cm−3as appropriate for proposed excimer lasers. Na is used as a prototype species, while its properties are varied to indicate some of the changes that could result from the use of different metals. The model includes sixteen excited levels of Na, three ionic species, the excimer levels of NaXe, and Na2. The degree of ionization is determined by collisional multistep excitation and ionization of excited atoms versus dissociative recombination of electrons with Na+2. Steady‐state conditions in the positive column are calculated for typical gas temperatures of ∼0.06 eV and electron temperaturesTeof 0.3–0.5 eV. The Na population distribution is largely Boltzmann at the electron temperature and the electron density is close to the Saha equilibrium value except at low electron temperatures and very high extracted laser powers. Useful gain and extracted powers of ∼10 MW/cm3are predicted for the higherTeand Na densities, with the pulse width limited to ∼10−7sec by gas heating. The model indicates that a metal which produces a deeply bound product state via dissociative recombination could yield a very efficient high‐power laser or gain cell.

ISSN:0021-8979    

DOI:10.1063/1.327825

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

With ferroelectric ceramic, principally BaTiO3dielectric capacitive coupling electrodes, simultaneous HF and DF pulsed laser action has been obtained as a function of [H2]/([H2]+[D2]) in H2+D2+SF6mixtures. The laser had a multiline output of 30 &mgr;J for an efficiency of 5.4×10−4at 120 pps. After 107pulses there has been no degradation of electrodes or decrease in laser performance. Alternate H‐source gases of CH4, C2H6, and C3H8had lower HF laser output than H2.

ISSN:0021-8979    

DOI:10.1063/1.327826

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An electro‐optic directional coupler switch has been fabricated with a GaAs homojunction structure and tested at 1.15 &mgr;m. Each single mode guide is made in an‐LPE layer grown on an+substrate, thep+rib used to confine the light being obtained by Zn diffusion and chemical etching. A calculation of the losses in the planar approximation roughly yields the large values of attenuation measured for TE and TM modes (∼8 cm−1). By reversely biasing the ’’stepped &Dgr;&bgr;’’ junctions with less than 17 V, more than 13 dB power isolation has been achieved for both switching states on a 6.3‐mm‐long device. Large improvements of the characteristics are expected from the additional design parameters provided by GaAs‐GaAlAs double heterostructure.

ISSN:0021-8979    

DOI:10.1063/1.327817

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Extensive data are presented on various photopumped multiple‐quantum‐well AlxGa1−xAs‐GaAs heterostructures, grown by metalorganic chemical vapor deposition, showing the variety of laser operation that can be observed one and two phonons below the lowest (n=1,n′=1′) confined‐particle electron‐to‐heavy‐hole (e→hh,n) and electron‐to‐light‐hole (e→lh,n′) recombination transitions. These experiments are performed on small cleaved rectangular samples that, because of two identifiable sets of orthogonal coupled modes, permit unambiguous identification of laser operation on LO‐phonon sidebands below the confined‐particle transitions. For a small number (two) of closely coupled (∼50 A˚) GaAs quantum wells of sizeLz∼50 A˚ laser operation occurs on multiples of h&slash;&ohgr;LOfrom one phonon below transitionn=1 (E1) to within a phonon or two of theLindirect band edge. AlxGa1−xAs‐GaAs heterostructures with more coupled GaAs quantum wells readily permit observation of laser operationtwophonons below the lowest confined‐particle transitions. Besides the use of size to reduce carrier scattering to lower energies in a GaAs quantum well, high Zn doping is used to screen and reduce the electron‐phonon interaction and thus reduce the carrier scattering to lower energies. The strong phonon participation in the laser operation of these quantum‐well heterostructures, which are not superlattices, demonstrates that the electron‐phonon interaction observed in this work is a true two‐dimensional effect (and not, e.g., the effect of Brillouin‐zone folding). An analysis and arguments are presented justifying this statement and, in addition, leading to the important conclusion that stimulated phonon emission is possible and might play (or likely plays) a role in the quantum‐well heterostructures of this work.

ISSN:0021-8979    

DOI:10.1063/1.327818

出版商:AIP    

年代:1980

数据来源: AIP