摘要:

Particle sizing uncertainties were calculated for the visibility and phase response functions of a dual‐beam laser Doppler velocimeter. This uncertainty primarily results from the nonmonotonic behavior of the response functions versus particle size and varies with particle index of refraction and the velocimeter optical configuration, in particular the receiving lens diameter and location. An exact Mie‐scattering algorithm predicted the velocimeter response functions for a number of particle indices of refraction and a variety of receiving lens configurations. Uncertainties were determined from the predicted particle size parameter increments corresponding to unit increments in the associated response functions. When examining uncertainties for particles with different refractive indices, the minimum and maximum response function values were used to obtain the associated size parameter increments. Particle sizing uncertainties tend to increase with the particle index of refraction for both visibility and phase. Receiving lens locations for minimal size measurement uncertainties are generally in the backscatter direction for visibility, and in the forward scattering direction near the incident beam plane, with a zenith angle of about 60°, for phase. A large receiving lens (f/♯≊1) minimizes uncertainties for visibility while a moderate lens (f/♯≊2) minimizes uncertainties for phase. Phase generally provides small uncertainties for particles with the same index of refraction but visibility provides smaller uncertainties when the particles have a range of refractive indices.

ISSN:0021-8979    

DOI:10.1063/1.350224

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A standard matrix method for tracing rays through an ion optical system is extended to include a recently discovered [W. Z. Liu and F. D. Bechetti, Rev. Sci. Instrum.60, 1228 (1989)] defocusing solenoidal lens. The results of the matrix approach are shown to correspond with results obtained by numerical integration of particle trajectories through real coil configurations. First‐order radial miss distances due to radial divergence of the beam, chromatic aberration of the lens system, and physical extent of the source are compared for one and two lens systems using the matrix formulation. It is demonstrated that a two lens system in a focusing‐defocusing arrangement can simultaneously correct to first order for chromatic aberration and beam divergence, producing a better focus for thin annular beams with significant energy spread and divergence. A new calculation of the focal length for the negative solenoidal lens is also included.

ISSN:0021-8979    

DOI:10.1063/1.350225

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present a theoretical analysis of a system composed of two periodic structures separated by a uniform waveguide section, taking into consideration the impedance mismatch at both ends of the system. First we examine the effect of the reflections on the output gain for a single stage system, i.e., when the uniform waveguide is not present. It is shown that if the product of the gain and the reflection coefficients is of order of unity, the output gain might be significantly smaller than the one‐pass gain as calculated by ignoring reflections. Introducing the uniform waveguide section, additional reflections occur from the two new planes of impedance mismatch. However, a proper location of these planes generates a wave, in the first slow wave structure, that practically may cancel the wave reflected toward the input end. The principle is similar to quarter wavelength tuning in transmission line or optical systems. The main difference is the fact that the electrons may have a significant influence on the waves, affecting the tuning condition.

ISSN:0021-8979    

DOI:10.1063/1.350226

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A new theory of absorption of microwave power by a lossy dielectric sphere in a resonant rectangular chamber is developed here. In this treatment, resonant modes of the cavity are resolved into traveling plane‐wave fields, and Mie’s theory of scattering and absorption of a plane electromagnetic wave by a sphere is utilized. The fields in the cavity containing the sphere are found by superposition of results for the individual scattering problem for each traveling plane wave. Absorbed power is then calculated by evaluating the time‐averaged Poynting vector and integrating over the surface of the sphere. Applications of microwave power absorption are discussed, with particular emphasis on processing of materials. Numerical studies based on the newly derived formulas are presented. The results exhibit the manner in which microwave absorption is influenced by a number of different experimentally controllable parameters. The examples considered were chosen with a view toward designing experiments and apparatus for containerless processing of materials in the microgravity environment of space.

ISSN:0021-8979    

DOI:10.1063/1.350227

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Analysis of blue/green/red coherent light radiated by surface‐emitting nonlinear generators is presented. It is shown that there are possibilities of obtaining efficient mW visible light out of these devices. Several problems in the calculation of the efficiency of these structures are discussed. These include the incorporation of the second‐harmonic reflections at the layer boundaries, the field and power continuity requirements, relation of device performances on different substrate orientations due to symmetry of the III‐V crystals, and an analysis of active surface‐emitting second‐harmonic generators.

ISSN:0021-8979    

DOI:10.1063/1.350228

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

O2(1&Dgr;)is generated in a bubble column reactor by the reaction between chlorine diluted in inert gas and a basic hydrogen peroxide solution. It is fed to an oxygen‐iodine laser system designed to operate under supersonic conditions. The O2(1&Dgr;) yield is measured as a function of the time elapsed from the onset of bubbling, type of diluent, and molar flow rate of chlorine and diluent. The yield when the chlorine is diluted with helium is significantly higher than when diluted with argon. This is explained as a consequence of the shorter residence time of the mixtures with helium where the molecular weight is smaller. A model that accounts for realistic physical and chemical processes in this system is presented. The model is divided into two stages which together describe the processes that occur between the reactor inlet and the measuring point of the O2(1&Dgr;) (before the supersonic nozzles). The first stage describes the processes occurring in the solution. It employs the film model for a fast reaction regime to describe the chlorine absorption, rather than film models where the instantaneous reaction regime is assumed and models assuming instantaneous absorption at the sparger outlet. The second stage describes the processes occurring in the gas phase above the solution. A good agreement between the model predictions and O2(1&Dgr;) yield data from this and other studies is obtained. In particular, the model accounts for the optimal clear liquid height in the reactor. Since the process of chlorine absorption and O2(1&Dgr;) production in the film is common to other types of reactor, the model can be used as a basis for analyzing the performance of those reactors as well.

ISSN:0021-8979    

DOI:10.1063/1.350229

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The concept of photothermal wave imaging has been adapted to the nondestructive inspection of transparent polymeric samples by specific generation of thermal waves. Utilization of light sources according to the absorption properties of the material secured pure surface heating which is necessary for sensible measurements. Thickness profiles of thin films made of poly(ethylene terephthalate), which are transparent in the visible spectrum, could be measured using a pulsed KrF laser. Examples for the nondestructive inspection of complex textile samples such as coated fabrics are presented.The photothermal analysis (PTA) of optically generated thermal waves is a powerful tool for nondestructive, contactless inspection and evaluation of intrinsic properties of a sample.1,2The method has been used for the observation of dynamic processes in adhesives, for the inspection of coatings on metal and of carbon fiber composites. A modulated light source, e.g., a chopped HeNe‐ or Ar+laser, is used for local, modulated heating at the sample’s surface resulting in a time‐ and space‐dependent temperature modulation which propagates through the material. In the case of a homogeneous layer heated only in a small volume at the surface the solution of the heat diffusion equation gives a heavily damped thermal waveT(x,y,z;t). In a one‐dimensional model3only the directionzperpendicular to the surface is considered and we obtain

ISSN:0021-8979    

DOI:10.1063/1.350230

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The problem of the thermochemical modification of chromium films is studied. The oxidation of the thin film on the glass wafer produced by local heating using laser radiation is considered. The temperature distribution is calculated. The width of recording trace is defined. The results of the experimental studies are presented and compared with the theoretical calculations. The effects of the parameter variations on the recording trace width are studied. The optimal conditions for optical recordings is defined.

ISSN:0021-8979    

DOI:10.1063/1.350231

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The power generation in a gasdynamic laser (GDL) has been theoretically studied. Quasi‐one‐dimensional unsteady flow equations are numerically solved simultaneously with the rate equation for the laser intensity inside the laser cavity. Steady‐state coupled solutions for the field variables and the laser intensity inside the GDL cavity are obtained by a time‐dependent numerical technique. The laser intensity variations along the axis of the flow (across the laser cavity) are computed for different laser gas mixture compositions and reservoir conditions. The analysis predicts a sharp spike in the laser intensity at the leading edge of the laser cavity followed by a sharp fall from which it recovers to a uniform constant value for the lower H2O concentrations. It is shown that the H2O concentration above 2% in the CO2‐N2‐H2O gas mixture is detrimental to the power generation.

ISSN:0021-8979    

DOI:10.1063/1.350232

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The input/output characteristic of a large aperture (270‐mm diam) electron‐beam‐pumped KrF laser amplifier is obtained for pulses of 6‐ and 40‐ps duration. The off‐resonance absorption coefficient is estimated by measurement of loss at 268 nm. The gain‐to‐loss ratio is found to decrease from 8 to 6 as the specific pump rate is increased from 0.3 to 0.65 MW cm−3. Gain depumping due to amplified spontaneous emission (ASE) is treated by a simple 1D code and found to give good agreement with experiment. A 3D code incorporating wall reflections gives even better agreement. The spatial distribution of gain and ASE is recorded using visible and ultraviolet imaging.

ISSN:0021-8979    

DOI:10.1063/1.350233

出版商:AIP    

年代:1991

数据来源: AIP