摘要:

Results are presented for the stopping power for protons of 1–100 MeV energy by Ni+nions with 0≤n≤26. Older Al stopping power results are re‐examined to better estimate and reduce the error, new asymptotic stopping power parameters are obtained from improved Al and Ni ion optical oscillator strengths, and Ni stopping power results are presented with an estimated accuracy of 20%.

ISSN:0021-8979    

DOI:10.1063/1.349764

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Outer surfaces of simple objects such as plates, cylinders, spheres, etc. may be approximately reproduced (in an infinite number of ways) by closely assembling a number of insulated metal stripes or wires. If those stripes or wires are then suitably connected through purely reactive impedances, one obtains a system that exhibits either ‘‘magnetostatic’’ or ‘‘electrostatic’’ modes. These modes are analogous to those predicted and observed in solid bodies of corresponding shapes (plate, cylinder, sphere, etc.) made of respectively magnetic or dielectric materials. The proposed systems can thus constitute models on which a number of basic features characterizing the magnetostatic or electrostatic modes can be easily demonstrated and studied. Two specific examples, the ‘‘magnetic’’ plate, and the ‘‘magnetic’’ cylinder, will be described in detail in this paper, both theoretically and experimentally. Other models exhibiting electrostatic modes will also be presented but only on the theoretical side.

ISSN:0021-8979    

DOI:10.1063/1.349765

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A scheme with the potential for generation of an electron beam with high brightness and several &mgr;s pulse duration for microwave generation, electron accelerators, or free electron lasers is investigated experimentally. An electron beam is extracted transversely to the flow of a plasma jet. The transverse boundary of the plasma allows extraction of a space charge limited electron current for 7 &mgr;s at a current density of 18 A/cm2. At present, a normalized microscopic brightness of 8×108A m−2rad−2is achieved. Closure of the extraction gap by invasion of plasma has been observed with a typical velocity of 0.1 cm/&mgr;s. Higher current density and higher brightness are expected for higher plasma densities and larger extraction fields.

ISSN:0021-8979    

DOI:10.1063/1.349766

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Upconversion‐pumped lasing characteristics near 3 &mgr;m on the4I11/2‐4I13/2transition of the Er3+ion in Er:YSGG (erbium‐yttrium‐scandium‐gallium garnet) and Er:YAG (erbium‐yttrium‐aluminum‐garnet), laser state spectroscopy, and population kinetics, are the main subjects discussed. The wide difference in lasing patterns of both garnets can be attributed to the difference in population inversion kinetics which was studied by analyzing the rise and decay of fluorescence starting from the laser states. It is shown that the effective decay times, &tgr;1and &tgr;2of the lower and upper laser states, are changed during lasing by the nonlinear energy‐transfer processes such that the resulting ratio becomes &tgr;1/&tgr;2<1. In Er:YSGG this condition is established during the declining phase of the4I11/2population, whereas in Er:YAG it occurs only for a short time during the rising phase. Consequently Er:YAG lases in a self‐terminating pulsed mode. The role of various energy‐transfer processes in the upconversion‐pumped population inversion kinetics is discussed and analyzed. It is experimentally shown that the lower4I13/2laser state in both garnets is depopulated by the cooperative energy summing due to the di‐ and tri‐ionic interactions. Because of these interactions, the4I11/2and4S3/2states are populated with ensuing fluorescence from these states at 980 and 550 nm, respectively. The indication that the latter state is populated directly by the tri‐ionic interaction, rather than via the former state by two sequential ion‐pair interactions, follows from the experimental fact that the 550‐nm fluorescence rises faster and reaches its maximum sooner than the 980‐nm fluorescence. The previously proposed kinetic rate equations for Er:YAG and Er:YSGG were modified by adding a cubic term to represent the tri‐ionic interaction. The steady‐state solutions yielded approximately cubic dependence of green fluorescence intensity on the intensity of pump radiation in agreement with the experiment. These solutions also explained deviations from cubic dependence observed experimentally in several erbium‐doped crystals.

ISSN:0021-8979    

DOI:10.1063/1.349767

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present a numerical investigation of all‐optical switching of solitons in two‐ and three‐core nonlinear fiber couplers. Both self‐switching of solitons and phase‐sensitive switching are considered. The extension of the results to multicore couplers is briefly discussed.

ISSN:0021-8979    

DOI:10.1063/1.349768

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Second‐ and third‐harmonic generations in ultrathin (200‐A˚)films of fluoro‐bridged aluminum phthalocyanine polymer have been observed in the geometry of Maker fringe experiment using Nd:YAG laser fundamental light. Two types of films, single‐crystalline and polycrystalline films, with different orientations grown by the molecular‐beam epitaxy technique have been used. Observed dependence of the generated second‐ and third‐harmonic intensities on the polarization of light and the angle of incidence is discussed based on the symmetry of the film structures. Enhancement of the harmonic intensities is realized in the single‐crystalline film.

ISSN:0021-8979    

DOI:10.1063/1.349769

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A copolymer of methyl methacrylate and azo‐dye‐substituted methacrylate is corona‐poled. Cerenkov‐type second‐harmonic generation (SHG) of Nd:YAG laser is observed in the poled polymer waveguide even though there is strong absorption of the SHG wavelength. The total SHG conversion efficiency is 1.72 × 10−3%, and the net SHG conversion efficiency in the waveguide is 0.21%.

ISSN:0021-8979    

DOI:10.1063/1.349770

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Output characteristics of an optically pumped tantalum vapor laser and the distribution of tantalum vapor generated by irradiation of a laser have been investigated experimentally. Ta vapor is generated by irradiation of a pulsed YAG laser and then the Ta atoms are optically pumped by a KrF excimer laser. It is observed that the maximum output energy is 160 nJ, the maximum optical conversion efficiency is 0.01%, and the ground‐state Ta atoms are distributed not only in the luminous space of the vapor but also around it.

ISSN:0021-8979    

DOI:10.1063/1.349771

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In this paper the authors applied an original transfer function method for calculations of radiation patterns in the case of Bessel circular transducers. It is known that the amplitudes of some natural vibration modes of circular plates are Bessel functions of zero order [R. R. Aggarval, JASA24, 463 (1952)]. In the paper the natural vibrational modes of a circular disk‐shaped ultrasonic transducer were employed. As it follows from the numerical calculations, it is possible to obtain for Bessel‐like transducers the nondiffracting main lobe. The latter is in accordance with the suggestions of the paper [J. Durnin, J. Opt. Soc. Am.4, 651 (1987)].  

ISSN:0021-8979    

DOI:10.1063/1.349772

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Pinch formation in fiber pinch experiments has been investigated in the lower terawatt regime. The main results are: (1) there are upper limits of breakdown voltage (∼700 kV) and current rise rate (∼20 kA/ns) beyond which leak discharges develop within the vacuum feed of the pulseline KALIF; (2) there is a lower limit of fiber radius (∼10 &mgr;m) below which pinch disruptions take place at a pinch current of ≳300 kA; (3) the hot (Te≤1 keV) inhomogeneous pinch plasma develops typically 10 ns after local collapses (micropinches) at a pinch current ≳400 kA and lives for more than 50 ns; (4) neutron emission (yield of CD2fibers ∼1010) appears mostly isotropic; (5) all fiber pinches show global expansion with velocities reaching from typically 10 &mgr;m/ns (initial expansion) to ≳100 &mgr;m/ns; and (6) the power requirements for the fiber ablation process are contradictory to those for the final pinch phase.

ISSN:0021-8979    

DOI:10.1063/1.349773

出版商:AIP    

年代:1991

数据来源: AIP