摘要:

Assemblies of hollow capillary tubes, termed ‘‘Kumakhov optics,’’ can be used to control x rays for a large variety of applications. Measurements of x‐ray transmission in polycapillary glass tubes were performed for the purpose of understanding their behavior in such devices. X‐ray transmission was measured for straight, uniformly curved, and nonuniformly bent fibers. The data agree well with a computer simulation based on classical ray tracing.

ISSN:0021-8979    

DOI:10.1063/1.355204

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The time centroid of the current pulse induced at the anode of a semiconductor drift detector is calculated as a function of the interaction coordinate for arbitrary drifting fields. The effects of its behavior on the determination of the absolute position of the interaction point are studied. For a typical bias condition of the detector, the paper shows that an error up to few hundred micrometers is made in the position reconstruction of the event if the described effects of the induction are not taken into account. The paper also shows that the time shift due to the perturbation of the drifting field caused by the discreteness of the field electrodes, is only of less than 1 ns, and therefore negligible in most applications.

ISSN:0021-8979    

DOI:10.1063/1.355205

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Based on the electron optical canonical aberration theory, up to the fifth‐order geometric aberrations have been analyzed for an equal diameter two‐tube electrostatic lens with the gap of 0.1 diameter and accelerating voltage ratio ranging from 5 to 40. The precisions are controlled rigorously at every step. For the computational results presented the computed first‐ and third‐order electron optical properties agree with the accurate values published in the literature of about 0.2%, and thus the fifth‐order aberration is believed to be acquired in a precision of about 1%. The contributions of third‐ and fifth‐order aberrations to the total aberration with respect to the filling factor or the accelerating voltage ratio have been first calculated numerically in the above‐mentioned electrostatic lens. The method of accurate numerical differentiation of an analytical or a digital function up to the sixth order would be expected to make a contribution to the development of computational electron optics.

ISSN:0021-8979    

DOI:10.1063/1.355206

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

One‐dimensional volume diffraction may be analyzed in a manner similar to the problem of an electron subject to a periodic potential. The quantity analogous to the diffraction Nath parameter &rgr; is then the ratio &Dgr;W0/V, whereVis the strength of the electron potential and &Dgr;W0the spacing between the free‐electron‐energy eigenstates. The crossover between the Bragg and Raman–Nath diffraction regimes is marked by a violation of the (1/&rgr;)≪1 condition, and corresponds to the requirement that (V/&Dgr;W0)≪1 in order to preclude electron eigenstate mixing. Bound‐state perturbation theory as developed for use in quantum mechanics may be applied to the diffraction problem to obtain a (1/&rgr;) expansion for the intensities of diffracted grating orders.

ISSN:0021-8979    

DOI:10.1063/1.355207

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Amplified spontaneous emission on the second xenon excimer continuum at 172 nm wavelength was observed in dense gas evaporated from a solid xenon surface and pumped by heavy ions. A pulsed 3.78 MeV Kr+beam from a radio‐frequency quadrupole accelerator was used for the experiment. A series of 800 &mgr;J particle pulses each 10 ns long was focused to a small, elliptical beam spot leading to a pump power density of the order of 1 GW/g. Optical gain in the target was deduced from the angular distribution of light emitted along the target axis, and from a variation of optical intensity with gain length. A maximum gain of 26%/cm was determined using a model calculation which reproduced the experimental data.

ISSN:0021-8979    

DOI:10.1063/1.355208

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We report on an optically activated phase modulator (OAM) and modulator array on GaAs‐GaAlAs compound semiconductor rib waveguides. A rib waveguide device with an optical activation window of 5 &mgr;m in diameter was fabricated. Optical activation was produced by using a HeNe 632.8 nm wavelength as the free‐carrier generator and a 1.3 &mgr;m laser as the signal carrier. A 33% modulation depth was observed and 10−2index modulation was experimentally confirmed on an OAM working in the phase modulation regime. OAMs working in both phase‐ and cutoff‐modulation regimes were further determined by considering the variation of the waveguide confinement factor. An 8.2 dB modulation depth was observed on an OAM working at the cutoff regime. Furthermore, the activation source for the free‐carrier generation is in the mW power region, which significantly reduces the size and cost of all optical switching devices.

ISSN:0021-8979    

DOI:10.1063/1.355209

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Experimental data on the 248 and 308 nm wavelength excimer laser ablation at poly(tetrafluoroethylene) doped with polymide (PI) are reported for a range of fluences and dopant concentrations. Threshold fluences were determined and a correlation was obtained between the dopant concentration and the threshold fluence. The threshold fluences and the limiting etch rates at high fluences decreased with increasing dopant concentration, and there is a minimum dopant concentration below which there is no ablation at both of the wavelengths. The side wall taper of the ablated holes increased with increasing dopant concentration. At subthreshold fluences, the polymer surface was modified with selective removal of PI from the polymer blend. The etch rates have been modeled using a two parameter thermal model to describe the etching process. The parameters obtained by fitting the data are qualitatively correlated to the dopant concentration and the measured limiting etch rates.

ISSN:0021-8979    

DOI:10.1063/1.355210

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A hot‐filament chemical vapor deposition reactor in which the substrate is a heated wire was used to analyze the energy transport to the substrate during diamond deposition. In this reactor, radiation and convection contribute negligibly to substrate heating. Atomic hydrogen recombination to molecular hydrogen on the substrate surface accounts for ∼90% of the energy reaching the substrate. The atomic hydrogen recombination rate and the thermal accommodation coefficient for the energy released by atomic hydrogen recombination were estimated frominsitumeasurements for tungsten and diamond surfaces. The atomic hydrogen concentration gradient was estimated for simple geometries. The experimental conditions under which atomic hydrogen transport to the substrate is diffusion controlled were found. Addition of methane reduced the atomic hydrogen recombination rate on the substrate. An optimum pressure was found for the transport of atomic hydrogen to the substrate.  

ISSN:0021-8979    

DOI:10.1063/1.355211

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Two‐dimensional ion velocity distribution functions are measured in electron cyclotron resonance (ECR) argon plasmas under a divergent magnetic field configuration using a directional analyzer. Ions produced in the ECR source grow to a beam in the downstream region inside an allowed angle, while the distribution function is almost isotropic outside the angle. The beam energy corresponds to the potential difference between the ECR source and downstream locations. The ion beam is almost parallel to an applied magnetic field, the beam being deflected along the divergent magnetic field lines. The energy spread and the temperature of the ion beam, and the temperature of the bulk ions are also shown as a function of the distance from the ECR source or of the gas pressure. The validity of the directional analyzer measurements is discussed by considering the motion of an ion in a sheath in front of the analyzer.  

ISSN:0021-8979    

DOI:10.1063/1.355212

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A mathematical model has been developed describing transport phenomena in gas‐metal arc welding. In the statement of the model a cylindrical electrode was considered and attention was concentrated on representing the electrodynamic, heat‐transfer, and fluid‐flow phenomena in the plasma column. Solutions were generated for the axisymmetric Maxwell’s equations, Navier–Stokes equations, and thermal‐energy balance equation for variable properties. The specific system considered involved the use of an aluminum electrode and argon as the shielding gas. Several current levels were explored and the theoretical predictions of temperatures were found to be in good agreement with spectroscopically measured temperatures. This appears to have been the first time that gas‐metal arc‐welding problems were treated in such a fundamental manner.

ISSN:0021-8979    

DOI:10.1063/1.355213

出版商:AIP    

年代:1993

数据来源: AIP