摘要:

A scalar field diffracted by a rigid rectangular plate can be computed with the formula that Otsuki derived by applying the properties of Weber–Schafheitlin’s discontinuous integral (also referred to as the Kobayashi potential). This method may be regarded as giving an eigenfunction expansion of the wave functions of the present configuration, although these functions are expressed by double infinite integrals. Expansion coefficients are determined from the matrix equations, and the matrix elements are given by double infinite integrals. An algorithm effective for computing these integrals is developed here by using the asymptotic expansions for the integrands. As a result, the original integral reduces to a finite double integral plus two finite single integrals. The numerical results for some diffraction patterns are presented. With relatively large plates, the results agree well with those obtained from the Kirchhoff diffraction integral. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366266

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The use of preferential etching and atomic force microscopy to measure refractive index profiles of optical fibers is investigated. Both the etch rate and the position of lateral features are shown to be independent of etch time. An elliptical core fiber was studied and the resultant profile was found to be in qualitative agreement with the preform index profile. It is shown, however, that the ellipticity of the core has changed during the drawing process. The method was extended to fluorine and germanium doped planar waveguides and the results correlated with the fabrication process. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366103

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The optimum performance of a regenerative Brayton cycle was analyzed. The model includes external and internal irreversibilities coming from four main sources: coupling to external heat reservoirs, turbine and compressor nonisentropic processes, pressure losses in the heater and the cooler, and the regenerator. In terms of the parameters accounting for each type of irreversibility, explicit numerical results are presented for the maximum efficiency, maximum power output, efficiency at maximum power output, power output at maximum efficiency, as well as for the pressure ratios required for maximum efficiency and maximum power. This analysis could provide a general theoretical tool for the optimal design and operation of real regenerative gas turbine power plants. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366104

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Distributions of the number of primary electrons produced per incident mono-energetic x-rays in the 1- to 41-keV energy range, which includes the xenonL- andK-absorption edges, were simulated in xenon gas detectors with the Monte Carlo technique. These simulated full-energy absorption distributions are calculated as frequency plots of the number of primary electrons produced per incident x-ray photon. The simulation includes the absorption of x-rays and the de-excitation of the residual xenon ions, followed by the development of the primary electron cloud. The discontinuities observed in the Fano factor,w-value, energy linearity and energy resolution reflect the discontinuities of the Xe photoionization cross-section at the photoabsorption edges. The simulation results are compared with experimental values measured with a gas proportional scintillation counter, and with recent data from other authors. The discontinuities in energy linearity produce an ambiguity in determining the x-ray energy in certain narrow ranges containing the edges. However, our simulation results permit a detailed analysis of observations in these regions. At theK-edge, the discontinuities in the calculated Fano factor and energy resolution were found to depend on the extent to which theK-fluorescence produced by the xenon atoms is allowed to escape. A discussion of the asymmetry of the calculated full-energy absorption peaks is made in terms of the distinction between the different decay branches initiated by photoionization of the Xe atoms, andK-fluorescence escape is found to influence strongly the skewness of the calculated distributions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366105

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Charge collection efficiency and the variance in the collected charge of semiconductor spectrometers are modeled. The model is based on a statistical approach and the extended Ramo theorem. The model yields an expression for variance in charge collection efficiency as a function of photon energy, bias voltage, and semiconductor parameters. These calculations as a function of absorption depth are particularly important in semiconductors with high atomic numbers, such as CdZnTe, since in these materials a uniform absorption cannot be assumed for a wide range of energies. Three different spectrometer configurations were considered: resistive, partially depleted Schottky barrier, and fully depleted Schottky barrier. An analytical model for the resistive configuration is presented and the results are compared to numerically obtained results of the Schottky configuration. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366106

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Short pulse laser-induced fluorescence experiments on the lowest-energy electronic states(&ugr;<10−4 cm−1)of trivalent praseodymium ions are reported. Crystals of lanthanum trichloride with a range ofPr3+concentrations were examined. We compute cross relaxation and upconversion coefficients for the metastable energy levels using a standard rate equation analysis. The limitations of the rate equation approach are examined with a focus on the underlying dynamics of this rare-earth system. The implications of these results for laser emission in the 1.3–7.2 &mgr;m spectral range are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366107

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article we carry out a careful investigation of the route to chaos exhibited by directly modulated semiconductor lasers as the modulation current amplitude is varied. The role played by the noise fluctuations in the route to chaos is analyzed. The laser is described by the rate equation model in which the noise is introduced through appropriate Langevin sources. For this analysis, we have first studied the dynamics of the underlying deterministic system. Using time integration, the bifurcation diagrams, when the modulation index is swept forwards and backwards, were obtained. These have provided only the stable solutions of the system. From these diagrams, the well known period doubling route to chaos is shown to coexist at certain intervals of the modulation index with a periodic three solution, showing a hysteresis phenomenon. Thorough explanation of the deterministic dynamics requires knowledge of unstable solutions, which we have found using a continuation method. This method reveals that the periodic three solution appears by a tangent bifurcation and that the hysteresis cycle involves chaotic bifurcations. At this point, we have introduced noise fluctuations, which allow the solutions to probe the surrounding dynamics. The route to chaos is found to be reversible and via period doubling, period quadrupling, and period tripling in agreement with experimental data. From this study, a consistent interpretation of the route to chaos was found in agreement with different experimental results. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366108

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fluorinated polyimide micro-objects (6–7.5 &mgr;m cross-sectional radius) fabricated using reactive ion etching have been both optically trapped and simultaneously rotated in both high and low relative–refractive index surrounding media. Symmetrical micro-objects with a low relative–refractive index were optically trapped by exerting optical radiation pressure through their center openings by using a strongly focused trapping laser beam. Micro-objects were both trapped and rotated by the radiation pressure when the horizontal cross sections of these objects showed dissymmetry (that is, not bilateral but rotational symmetry). In the case of micro-objects with a high relative–refractive index, the pressure is exerted on the outer walls. For objects with a low relative–refractive index, the pressure is exerted on the inner walls. The rotation speed versus optical power (typically, 0.4–0.7 rpm/mW) and the axial position of the laser focal point were investigated for high relative–refractive index micro-objects. The optically induced torque generated by aTEM01*(doughnut)-mode laser beam was found to be greater than that generated by aTEM00-mode laser beam. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366163

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this analysis, the generalized kinematic equation for the thickness of the molten film is derived by perturbation methods and the method of multiple scales is used to investigate the weakly nonlinear stability of the flow of molten material in laser cutting under a transverse uniform magnetic field, taking into account the effect of phase change at the liquid–vapor interface. Analysis of the linear stability of the molten layer shows that the optimum cutting speed can be increased through use of the magnetic field. Nonlinear stability analysis further shows that supercritical stability and subcritical instability exist in the laser cutting system with or without magnetic effect. In a magnetic field, the equilibrium amplitude of high cutting speeds decreases, and the minimum threshold amplitude increases at low cutting speeds. The effect of the magnetic field, measured by the Hartmann number(m)is to stabilize the flow regardless of the cutting speed value or gas velocity. An appropriate applied magnetic field improves the laser cutting process and counteracts surface roughness. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366109

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A study of the mechanical vibrations of a freely suspended (FS) ferroelectric liquid-crystal film has been carried out. Upon excitations by sound irradiation and also by electric-field application, the mechanical vibration of the FS film of the ferroelectric liquid crystal is effectively excited. In the frequency dependence, resonance vibrations are observed for both excitations and the resonance frequencies, and light reflection patterns are found to be different for both excitations, suggesting the different oscillating modes of the FS film for both excitations. In electric-field excitation, the vibration mode, which is consistent with the molecular model of the origin of the vibration due to the reorientation ofPsbyPs⋅Etorque is found. In addition, the application of the FS film of the ferroelectric liquid crystal as sensitive acoustic sensors is proposed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366162

出版商:AIP    

年代:1997

数据来源: AIP