摘要:

Data analysis in the laser‐pulse method of measuring thermal diffusivity is based on the solution of the heat diffusion equation, assuming several boundary and initial conditions. The initial condition generally results from considering the material opaque to the laser’s radiation. This requires building special absorbing layers on the sample’s surface when the material is transparent. A more general solution of the heat diffusion equation was obtained in this paper, in order to simplify sample preparation, and in some cases (high temperatures, sample contamination, etc.) even make possible the measurement of partially transparent materials. Based on an exponential‐like absorption of the laser’s radiation, the solution includes an absorption‐depth parameterp, which describes the material’s degree of transparency. A computer‐programmable data‐reduction procedure, including a least‐squares estimation algorithm of nonlinear parameters, was also developed. It permits the simultaneous determination of both the thermal diffusivity and the absorption depth from a single laser‐pulse experiment. The accuracy of the method was verified by measuring a sintered glass sample, both with the usual and the new procedures. The results indicate an accuracy level compatible with the current state of the art.

ISSN:0021-8979    

DOI:10.1063/1.339950

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We describe a surface laser‐light scattering (SLLS) spectrometer, which uses optical heterodyne detection to measure the temporal behavior of the thermally generated capillary waves at a fluid/fluid interface. From the measurement the interfacial tension and one of the bulk fluid viscosities are calculated. An instrument resolution model is described that characterizes the resolving power of the SLLS spectrometer based on the optical parameters measured at the photodetector. The instrument resolution is defined and measured, and the resolution is adjusted to optimize the signal‐to‐noise ratio. The model was verified using light‐scattering measurements with wave numbers in the range 250–1750 cm−1and with instrument resolution varied by more than a factor of 2. Measurements were made on several liquids whose viscosities vary over an order of magnitude. Data reduction used the analysis of thermally generated capillary waves recently published [A. Hajiloo and J. C. Slattery, J. Colloid Interface Sci.112, 325 (1986)]. The values calculated for both surface tensionandliquid bulk viscosity were in good agreement with the literature.

ISSN:0021-8979    

DOI:10.1063/1.339951

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We describe the realization of a source of Mg atoms in the metastable triplet 3s3p3Pand we report a theoretical model describing the dynamic process of production of metastable atoms via electron impact excitation. Experimental results concerning atomic flux and velocity distribution are reported and compared with the theoretical model; the efficiency of production of metastable atoms was 40%, in good agreement with the computed value, and the velocity distribution showed a dependence from the discharge current close to the theoretical prediction.

ISSN:0021-8979    

DOI:10.1063/1.339952

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Multiple scattering from a randomly rough surface is studied with the Kirchhoff approach. High‐order scatterings from the surface are contributed from the statistically distributed pairs of specular points. The shadowing effects in sequential scatterings are taken into account. An explicit formula is developed to compute the bistatic double‐scattering coefficient of polarized scattered waves.

ISSN:0021-8979    

DOI:10.1063/1.339953

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A study of dye solution flow characteristics in a planar dye laser cell, and their influence on the thermal properties affecting the optical quality of the lasing medium, particularly thermal lensing, is presented. Steady temperature gradients generated in the dye laser cell (∼10−3M rhodamine‐6G in methanol) by a high‐frequency repetitive copper vapor laser, extended from 1 to 2 mm upstream relative to the pump laser impact position to the entire cell length downstream. The steady nature of the gradients is related to vorticity of the dye solution flow, resulting in a 3–4 orders of magnitude apparent enhancement of the thermal diffusivity.

ISSN:0021-8979    

DOI:10.1063/1.339954

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Time‐dependent calculations of multiplexed short‐pulse amplification are presented which show that cascaded short pulses in KrF lasers, with an appropriate time interval between the pulses, can extract energy with only a small cost in extraction efficiency as compared to a single long pulse. This dynamic characteristic of KrF* permits the design of a novel, simpler angular multiplexing system. Calculations include nonsaturable and saturable absorption, amplified spontaneous emission effects, and an end mirror for double‐pass amplification. The dependence of the extraction efficiency and the energy gain on the time interval and pulse shape are calculated.

ISSN:0021-8979    

DOI:10.1063/1.339955

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The effect of buffer gases on the operating performance of a self‐sustained discharge ArF laser employing a charge transfer excitation circuit has been analyzed theoretically. By the analysis of the electron kinetics, the ArF* formation, the ArF* relaxation, and the absorption of theB→Xlaser radiation, the pump rate dependence of intrinsic efficiency, small‐signal gain, and absorption could be clarified for the Ne‐ and He‐diluted mixtures. It is found that there is no appreciable difference in the intrinsic efficiency of the ArF laser between Ne‐ and He‐diluted mixtures when employing a laser resonator with a strong output coupling. After optimizing output coupling in each case, a higher efficiency is obtainable for the Ne diluent than for the He diluent. For a 4‐atm mixture of 4.9% Ar and 0.1% F2in Ne, an intrinsic efficiency of 4% is obtainable, while less than 2% is obtainable for the He‐diluted mixtures. However, a higher specific output energy is achievable for the He‐diluted mixtures than the Ne‐diluted mixtures because the use of He‐diluted mixtures can efficiently transfer the stored energy to the laser discharge load.

ISSN:0021-8979    

DOI:10.1063/1.339956

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have modeled the properties of a transverse electron beam pumped argon ion laser using Monte Carlo techniques. We studied the lasing transitions at 4765 and 4880 A˚ for electron energies up to 300 eV, for conditions of pressure and degree of ionization similar to those employed in conventional lasers. We find lasing efficiencies to be comparable to those in the conventional axial discharge argon ion laser. However, it may be possible to attain higher efficiencies if much higher degrees of ionization can be reached.

ISSN:0021-8979    

DOI:10.1063/1.339957

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Fabrication and lasing characteristics of short cavity GaAs/AlGaAs multiquantum‐well (MQW) lasers with dry‐etched facets are described in detail. The lasers are fabricated from GaAs/AlGaAs double‐heterostructure wafers grown by molecular‐beam epitaxy. Fabry–Perot cavities are formed by a reactive ion‐beam etching technique with Cl2plasma. The dependence of lasing characteristics on the cavity length is examined. A threshold current as low as 30 mA is achieved for 20‐&mgr;m‐long cavity MQW lasers with 12 110‐A˚‐thick GaAs wells separated by 11 50‐A˚‐thick Al0.2Ga0.8As barriers. The very short cavity lasers with large mode spacing realize the stable single‐longitudinal‐mode operation. Furthermore, the lasers show good high‐frequency performance. A relaxation oscillation frequency as high as 32 GHz is observed with a 30‐&mgr;m‐long laser. Temperature characteristics are also presented.

ISSN:0021-8979    

DOI:10.1063/1.339958

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Analytical results are presented for the reflection of acoustic waves from liquid‐laminated composite interfaces. The composite is oriented such that the laminates are stacked normal to thex3directions with propagation confined to thex1‐x2plane. The fluid‐composite interface is assumed to be normal tox2. Because of the complex microstructure of composites, continuity conditions exist on both the macro (liquid/composite interface) and micro (laminate interface) scales. Because of the number and nature of these conditions, exact solutions are exceedingly difficult, if not impossible, to obtain. As an alternative, we formulate an approximate analysis in which the composite medium is replaced by a homogeneous, yet dispersive, medium. In the process of replacing the composite with such a material model, the microcontinuity conditions are utilized. Numerical results are presented to demonstrate the dispersive behavior of leaky surface waves on the composite.

ISSN:0021-8979    

DOI:10.1063/1.339959

出版商:AIP    

年代:1988

数据来源: AIP