摘要:

This paper presents a review on the latest state of the novel bulk devices, with an emphasis on lenses for electron beams. As one application of high critical‐temperature (Tc) bulk superconductors, the author proposed the lenses (Supertrons) and his group has developed them. The principle of the lenses is simple: When one injects electron beams into narrow superconducting tubes, the tubes confine the self‐magnetic field of the beams to the bore of the tubes because of the Meissner effect. The enhanced field accordingly focuses the beams into thinner ones. The first two sections outline high‐Tcsuperconducting materials and fundamental characteristics of electron beams. In the body of this article, the lenses are evaluated according to the focusing of intense electron beams (∼340 keV, ∼1 kA, ∼10 ns) and assigned a figure of merit. Lenses were made from powder‐pressed yttrium‐ (Tc=∼90 K), bismuth‐ (∼105 K), thallium‐ (∼120 K), and melt‐processed yttrium‐based superconductors. From the experimental results, one can say that powder‐pressed lenses are suitable for short pulsed, low repetition‐rate electron beams (a ferrite‐core model) and that melt‐processed lenses are, on the other hand, probably appropriate for continuous or slowly time‐varying electron beams. In addition to the temperature‐dependent focusing of the electron beams, a criterion for design of the lenses is discussed. To show the potential of the lenses, two applications of the lenses are described: a wiggler for free‐electron lasers and an electron‐beam guide for induction linear accelerators. Finally, other novel applications (current leads, magnets, and bearings) indicate the interest in bulk materials which are rapidly being developed. The review will provide fundamentals for potential applications of bulk superconductors.

ISSN:0021-8979    

DOI:10.1063/1.354944

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The Talbot effect in holography has been studied. The study has shown that in monochromatic illumination of a bleached off‐axis hologram of a periodic grating, self‐images of the grating are reconstructed in the real image region. These self‐images of the reconstructed grating appear not only in the rays of the ±1st orders but also in the zeroth diffraction order.

ISSN:0021-8979    

DOI:10.1063/1.355041

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Laser assisted particle removal (LAPR) is an innovative laser cleaning technique which can remove various particles from solid surfaces via laser induced explosive evaporation of a chosen energy transfer medium, e.g., water. An Ar+ion continuous‐wave laser (488 nm) was used to study the CO2laser pumped explosive evaporation of water adsorbed on a Si substrate. The probe laser beam was parallel to the sample surface at different displacements and interacted with the ejected material upon pulsed CO2laser irradiation in analogy with the time resolved laser beam deflection experiments on laser induced vaporization of copper by Guoetal. [Opt. Commun.77, 381 (1990)]. Using CO2laser energies which are much greater than the LAPR thresholds, we observed the generation and propagation of a shock wave at supersonic speeds followed by a water vapor/aerosol/particle cloud at a much slower speed. From the evolution of the shock wave, the total conversion efficiency of the incident laser beam into the shock wave has been determined using a self‐similar approximation.

ISSN:0021-8979    

DOI:10.1063/1.355017

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We employed a focused ion beam (FIB) to sputter the end mirrors on InGaP/InGaAlP laser diodes. This particular diode operates at a wavelength of about 670 nm. For this wavelength the quality of the sputtered mirrors is far more critical than for longer wavelength devices. The present lasers do, in fact, show a relatively large increase in their threshold current after FIB micromachining. In this article, we investigate the origins of this increase and how to prevent it. After optimization, the lasers with a FIB‐made end mirror have a threshold current comparable to that of cleaved‐facet devices. We have seen that the polycrystalline structure of the device metallization on top of the laser diode causes roughening of the mirror during sputtering, which results in severe scatter losses of the laser light. A method to decrease the surface roughness is given. A further reason for the increase in threshold current is optical absorption at the mirror, presumably by a Ga‐rich layer. This can be circumvented by chemical etching after FIB treatment to remove the absorbing layer. Finally, to demonstrate the quality and the applicability of the FIB‐made mirrors, the influence of the tilt angle of the end mirror on the threshold current of the laser has been investigated. This dependency can be excellently described by theory.

ISSN:0021-8979    

DOI:10.1063/1.355018

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The mirror temperature response of a diode laser to injection current is studied through the photodeflection method. A theoretical model is presented together with some experimental measurements. Theoretical results are compared with experimental measurements for an AlGaAs quantum well laser diode.

ISSN:0021-8979    

DOI:10.1063/1.355019

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We demonstrate asymmetric Fabry–Perot reflection modulators using both InGaAs and GaAs quantum wells which operate beyond the matching condition and exhibit zero phase change (zero chirp) when switched. These devices are structurally similar to devices which can operate before the matching condition, and with incorporation of only a small etch step enable planar realization of zero phase change modulators operating before and beyond the matching condition which reflect 180° out of phase. We also show how observation of the reflectivity spectrum can provide quick information about the voltage necessary to obtain this zero chirp behavior. These structures provide a basis for low chirp optical switching, beam steering, and spatial light modulation.

ISSN:0021-8979    

DOI:10.1063/1.355020

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

It has been shown that the resultant acceleration sensitivity of contoured quartz resonators vanishes for perfect symmetry of the resonator with respect to the support system. It has further been shown that any loss of symmetry in the combined resonator plus support configuration results in a linear increase in the acceleration sensitivity. Since it is impossible to construct a perfectly symmetric resonator plus support configuration in practice, a stiffened structure is investigated. The structure consists of the active biconvex quartz resonator attached to identical top and bottom quartz cover plates by means of small sidewalls around the periphery. The mounting clips are attached to the top and bottom cover plates without touching the active plate. An analysis of the linear increase in the in‐plane acceleration sensitivity of the stiffened configuration is performed. Results are presented which show the influence on the in‐plane and resultant acceleration sensitivities of differences in the properties of the clips and a mispositioning of either a clip or the mode shape for a range of thickness of the cover plates relative to the active plate.  

ISSN:0021-8979    

DOI:10.1063/1.355021

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The thermal diffusivity measurement through pulsed photodeflection in a modified collinear configuration is presented and discussed; comparison between theory and experiment is also shown.  

ISSN:0021-8979    

DOI:10.1063/1.355334

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A general solution to the hygrothermoelastic problem associated with an interface discontinuity between dissimilar anisotropic media is presented. The complex variable representation of Lekhnitskii [TheoryofElasticityofanAnisotropicElasticBody(Holden‐Day, San Francisco, CA, 1963)] is extended into the hygrothermoelastic problem by means of five complex functions including three stress functions, one temperature function, and one moisture function. A special technique of analytical continuation is used to deal with the continuous conditions of dissimilar media. Based on the Hilbert problem formulation, the linear relation between the boundaries of discontinuity can be derived into a type of Cauchy integral, which makes the solution in a compact version. The result shows that the heat or moisture flux exhibits an inverse square‐root singularity at the tips of discontinuity while the nature of singularity of the hygrothermal stresses possess the same trig‐log character as those obtained for the elastic problem.  

ISSN:0021-8979    

DOI:10.1063/1.355022

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A theory is presented to explain the observed electron emission characteristics of a hollow‐cathode‐based plasma source. The theory is compared with measurements made in a laboratory vacuum facility and is used to predict emission characteristics when the source plasma expands into an ambient space plasma. Crucial to understanding the observed emission current‐voltage characteristic of hollow‐cathode‐type devices is the recognition of the role of emission current, not just the current in the main discharge circuit, in ionization of the neutral gas flowing through the device. This ionization can lead to breakdown of the sort that is familiar in many gas discharge devices. Equally crucial to understanding the low impedance capability of the device in coupling spacecraft to an ambient space plasma is recognition of the role of escaping as well as trapped source electrons in the formation of the space potential profile. The presence of these electrons, according to the theory, results in space electron emission current‐voltage characteristics which are well approximated by those observed in laboratory chambers.

ISSN:0021-8979    

DOI:10.1063/1.355023

出版商:AIP    

年代:1993

数据来源: AIP