摘要:

In a dielectric‐loaded waveguide a slow rotating equilibrium of a relativistic electron beam which interacts with the electromagnetic waves is investigated in a self‐consistent way. General dispersion relations for the fundamental transverse magnetic modes in the presence of the external magnetic field are derived using the cold fluid Maxwell equations and the appropriate boundary conditions. For slow space charge and slow cyclotron modes an algebraic equation is obtained from the dispersion relation by using a tenuous beam approximation. Solutions of the resulting equation are obtained for variations of several parameters, such as the external magnetic field, the dielectric constant, the thickness of the dielectric material, and the gap between beam and dielectric materials. With the beam‐dielectric gap satisfying the stability condition, the growth rate of the space charge and the slow cyclotron instabilities show the same behavior as previous results for the no gap case [IEEE Trans. Plasma Sci.PS‐17576 (1989)]. Finally, emphasis in the analysis is given to the effect of the finite gap between the beam and dielectric and the comparison to the previous study of a no‐gap case. From this analysis it is also shown that as the gap width increases, the growth rate, &ohgr;icdecreases due to the finite geometric effect related to the gap width.

ISSN:0021-8979    

DOI:10.1063/1.346654

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The uniformity of focused laser beams, that has been modified with randomly phased distributed phase plates [C. B. Burckhardt, Appl. Opt.9, 695 (1970); Kato and Mima, Appl. Phys. B29, 186 (1982); Katoetal., Phys. Rev. Lett.53, 1057 (1984); LLE Rev.33, 1 (1987)], can be improved further by constructing patterns of phase elements which minimize phase correlations over small separations. Long‐wavelength nonuniformities in the intensity distribution, which are relatively difficult to overcome in the target by thermal smoothing and in the laser by, e.g., spectral dispersion [Skupskyetal., J. Appl. Phys.66, 3456 (1989); LLE Rev.36, 158 (1989);37, 29 (1989);37, 40 (1989)], result largely from short‐range phase correlations between phase plate elements. To reduce the long‐wavelength structure, we have constructed phase patterns with smaller short‐range correlations than would occur randomly. Calculations show that long‐wavelength nonuniformities in single‐beam intensity patterns can be reduced with these masks when the intrinsic phase error of the beam falls below certain limits. We show the effect of this improvement on uniformity for spherical irradiation by a multibeam system.

ISSN:0021-8979    

DOI:10.1063/1.346655

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The carrier generated by a solid‐state laser can be frequency shifted by a significant amount. This fact was exploited to implement a high‐resolution optical‐fiber fault locator. A resolution of 4 mm was achieved. Compared to the resolution of a frequency‐domain reflectometer that shifts the frequency of the AM modulation of the light, the proposed fault locator has a resolution about 1000 times better. The potential of developing the proposed reflectometer into an ultrahigh‐resolution integrated optics fault locator is also discussed. UFaipxr

ISSN:0021-8979    

DOI:10.1063/1.347179

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Cathodoluminescence and electron beam induced current are used to investigate the degradation of the graded‐index separate‐confining heterostructure laser devices grown on silicon substrates. By examining the evolution of the microscopic electronic properties of these devices during operation or under electron beam bombardment, a better understanding of the initial mechanism of degradation in a laser device results: it is concluded from this study that the degradation starts in the vicinity of thep‐njunction before attaining the active layer or the formation of dark line defects. This starting of degradation is attributed to the point‐defect migration or coupling in the space‐charge region. The built‐in electrical field plus the nonradiative recombination of excesses carriers seems to be related to these phenomena. It is also pointed out that the technological processes for device fabrication have a strong influence on the degradation mechanism.

ISSN:0021-8979    

DOI:10.1063/1.346656

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We describe the current status of tunable, cw, solid‐state lasers in the infrared region of the spectrum which may be tuned to the helium resonance transition near 1083 nm. The principal use for these laser devices is the optical pumping of3He and4He atoms via the 23S1metastable state. The tunable lasers we have examined include Nd3+‐doped YAlO3, LaxNd1−xMgAl11O19(x∼0.15), Nd:LiNbO3, and Nd:silica glass fibers. Power outputs from these lasers range from a milliwatt to more than 1 W at the helium transition. Laser emission bandwidths range from less than 40 MHz (single‐mode operation) to several GHz. Applications include magnetometry, dense nuclear targets, and polarized electron beams.

ISSN:0021-8979    

DOI:10.1063/1.346657

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An LNA (Nd‐doped lanthanum‐hexaluminate) crystal has been pumped with a cw, krypton arc lamp in a commercial Nd:YAG cavity. The cw output power greater than 6 W is obtained in a 28‐cm long, plane mirror cavity. The free‐running wavelength is near 1083 nm and has a width of about 0.8 nm. Inserting a 0.25 mm thick, uncoated solid etalon in the cavity permits the laser output to be continuously tuned from 1082 to 1084 nm by tilting the etalon. The laser bandwidth is reduced to below 0.016 nm. Over 3 W are obtained at the helium resonance transition. The maximum power output is limited by severe thermal lensing effects in the LNA crystal. The single, arc‐lamp pump is operated at less than 70% of its maximum rated current; thus, substantial increases in the power output can be expected if crystal quality can be improved.

ISSN:0021-8979    

DOI:10.1063/1.346658

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new model of ‘‘new donors’’ is presented, based on electrical, infrared measurements, transmission electron microscopy, and high‐resolution electron microscopy observations on Czochralski‐grown silicon single crystals containing ‘‘new donors.’’ In this model, the electrical activity of ‘‘new donors’’ originates from the uncoordinated Si dangling bonds on small dislocation loops resulting from oxygen precipitation. In comparison with other models, the present model can better explain the experimental results of the heat treatment Czochralski‐grown Si wafers.

ISSN:0021-8979    

DOI:10.1063/1.346659

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

First, an overview of the present state of art of imaging of three‐dimensional particle (or damage) distributions in the field of ion implantation is given. Usually, the direct measurement of three‐dimensional distributions in the field of ion implantation is restricted to cases when the impinging ion beam diameter is small against the size of the corresponding distributions, i.e., to ion energies above typically 100 MeV and to microbeams of a few &mgr;m diameter. To gain information also for lower ion energies without the restriction in the beam diameter, a modified tomographic reconstruction technique has been developed recently by us and is described here in detail. Three‐dimensional distributions are reconstructed from a number of one‐dimensional depth profiles, implanted under various angles. Competing algorithms for the solution are discussed. For the mathematical technique chosen, some consistency tests are presented. Good accuracy of a sufficient number of input profiles is vital for the quality of the three‐dimensional reconstruction

ISSN:0021-8979    

DOI:10.1063/1.346660

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Pulsed schlieren photography and fast helium‐neon laser deflection are used to study the hydrodynamics of laser ablation of polyethyleneterephthalate and polymethylmethacrylate by pulsed KrF (248 nm) radiation in atmospheric air, Ar and N2. Schlieren measurements show the evolution of shock waves, sound waves, and reduced‐density, hot gas plumes. A transition from sound to shock at the ablation threshold for both polymers is observed. The shock velocity of PET tends to approach agreement with blast wave theory at fluences higher than 1 J/cm2. Plumes in air are consistently larger than those produced in Ar and N2(at fluences below 5 J/cm2) suggesting that combustion may occur. Laser deflection measurements for PET at 150 mJ/cm2indicate a plume density of 0.6 kg/m3(50% atmospheric density).

ISSN:0021-8979    

DOI:10.1063/1.346661

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report for the first time the successful application of the leaky tube method to diffuse elemental Cd into InP at 500 °C. Specular surfaces are consistently realized while additional phosphorus in the ambient is not required. Free‐carrier concentration profiles and junction depths were experimentally determined for times ranging from 20 min to 21/2 h. A reproducible surface concentration of ionized acceptors is ∼1×1018cm−3(T=300 K). A concentration dependent diffusion coefficient ranging from approximately 1×10−14to 1×10−10cm2/s is calculated for the conditions under investigation. Secondary ion mass spectroscopy analysis shows the atomic Cd concentration to be very similar to that of the ionized acceptors, with the atomic surface concentration approximately two times greater than the surface hole concentration.

ISSN:0021-8979    

DOI:10.1063/1.346662

出版商:AIP    

年代:1990

数据来源: AIP