摘要:

Interparticle force measurements have been performed upon various configurations of linear chains and planar layers of chrome steel balls immersed in a steady uniform applied magnetic field. These force measurements, made for particles in contact and at various separations, reveal that the attractive forces are enhanced in the case of particle chains parallel to the applied magnetic field and slightly decreased in the case of perpendicular layers. The magnetic saturation exhibited by the steel balls has only a modest effect on the force. Experimental data obtained for two‐particle chains correlate reasonably well to force calculations based upon a linear multipolar expansion using a relative particle permeability value of &mgr;r=100. It is also found that data obtained with longer linear chains as well as with planar particle arrays do not deviate drastically from the predictions of the two‐sphere problem.

ISSN:0021-8979    

DOI:10.1063/1.352916

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have studied the temperature sensitivity of strained‐layer InGaAs/Ga(In)As(P)/GaInP separate‐confinement‐heterostructure quantum well lasers emitting at &lgr;∼980 nm. We observed that the lasers with GaAs confinement layers exhibited higher temperature sensitivity than those with GaInAsP confinement layers. It was also found that using the GaAs confinement layers, the lasing characteristics dramatically degraded at elevated temperatures, in particular, as the quantum well width was reduced. These phenomena could be attributed to a poor carrier confinement present in the case of InGaAs/GaAs quantum wells.

ISSN:0021-8979    

DOI:10.1063/1.352917

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The optical properties of grating coupled waveguides are theoretically modeled and practically demonstrated using nematic and smectic liquid crystals as thin (0.7 &mgr;m) waveguide layers. Voltage induced reorientation of the liquid crystal is shown to lead to large changes in reflectivity and transmissivity when the angle of incidence initially corresponds to a guided mode resonance. Time resolved measurements using these thin cells show that the switching time for the nematic phase can be faster than the smectic phase.

ISSN:0021-8979    

DOI:10.1063/1.352918

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The potassium of KTiOPO4has been exchanged for protons or ammonium ions to form optical waveguides. Proton exchange is relatively fast, does not give depth profiles expected for diffusive processes, and distinct potassium‐depleted phases are formed. The kinetics for ammonium exchange are relatively slow and diffusion limited, similar to those for Rb and Tl exchange processes. Increases in surface refractive index of up to 0.053 for proton exchange and 0.046 for ammonium exchange have been observed, with higher values for mixed NH4/H and Rb/H exchanges.  

ISSN:0021-8979    

DOI:10.1063/1.352919

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Laser parameters for the 1.73 &mgr;m (5d[3/2]1−6p[5/2]2) xenon transition in fission‐fragment excited Ar/Xe, He/Ar/Xe, Ne/Ar/Xe, and He/Ne/Ar/Xe gas mixtures are presented. Using a cw F center laser, time resolved small signal gain was probed as a function of total pressure, xenon concentration, pump power, He/Ne/Ar buffer ratio and impurity concentration. Small signal gains of up to 2%/cm were observed for pump rates of 30 W/cm3. Addition of helium and/or neon to the argon buffer increased the width of the time resolved laser gain pulse and reduced the absorption observed under some experimental conditions. Experimentally determined gain scaling laws for several gas mixtures are presented. The measured small signal gain was coupled with the results of laser cavity measurements to calculate the saturation intensity for several gas mixtures. The addition of helium or neon increases the saturation intensity for several gas mixtures. Laser cavity measurements as well as the gain × saturation intensity product indicate that the 1.73 &mgr;m power efficiency is approximately 2% for several gas mixtures.

ISSN:0021-8979    

DOI:10.1063/1.352920

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The results of small signal gain measurements of the 2.03 &mgr;m (5d[3/2]1−6p[3/2]1) xenon transition in fission‐fragment excited Ar/Xe, He/Ar/Xe, Ne/Ar/Xe, and He/Ne/Ar/Xe gas mixtures is presented. Time resolved small signal gain was probed using a cw He/Xe discharge laser as a function of total pressure, xenon concentration, pump power, He/Ne/Ar buffer ratio, and impurity concentration. Small signal gains of up to 6%/cm were observed for pump rates of 15 W/cm3. Addition of helium and/or neon to the argon buffer increased the width of the laser gain and reduced the absorption observed under some experimental conditions. Experimentally determined gain scaling laws for several gas mixtures are presented.

ISSN:0021-8979    

DOI:10.1063/1.352921

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In an elastically isotropic semiinfinite medium having a free surface with a weak harmonic corrugation, the interaction between the Rayleigh wave guided along the free surface and the shear vertical and pressure bulk elastic waves propagating in the substrate is investigated for the propagation directions lying in a plane perpendicular to the average free surface and containing the grating vector. The governing equations of this interaction are deduced and are shown to be consistent with the requirements of reciprocity and power conservation. The theory is applied to determine the characteristics of the output coupler in which the Rayleigh wave guided along the free surface radiates the bulk elastic waves in the substrate as well as those of an input coupler in which the shear and the pressure bulk elastic waves in the substrate incident on the corrugated region of the free surface launches the Rayleigh wave. Techniques for optimizing the performance of the input coupler to achieve maximum excitation efficiency of the Rayleigh wave are examined. The characteristics of these transducers are presented with the help of some illustrative numerical results.

ISSN:0021-8979    

DOI:10.1063/1.352922

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The critical plasma parameters for plasma source ion implantation (PSII) are the ion implantation current, the sheath expansion characteristic, the energy of the implanted ions, and the electric field intensity on the electrode surface. These quantities have been calculated for spherical electrodes using a fluid dynamic model. The results show that for the implantation time larger than ten ion plasma periods, both the ion current and the sheath expansion characteristic of the fluid dynamic model are consistent with that of the previous analytic models. But for implantation time less than ten ion plasma periods, the results are quite different. As the sphere radius gets smaller, the difference in the results becomes greater. In our experiments, the measured cathode current and the sheath expansion characteristic of the spherical cathode are shown to fit the fluid dynamic model better. The negative high voltage pulse employed in our experiments has a rising edge of less than 1 &mgr;s and a flat top approaching the theoretical model. The secondary electron emission coefficients for stainless steel and copper under PSII conditions have also been estimated using two different methods: retarding static electric field energy analyzer and the cathode current measurement. It is found that under PSII conditions, secondary electron emission coefficients are in general larger than the values taken under the condition of atomically clean surfaces in ultrahigh vacuum.

ISSN:0021-8979    

DOI:10.1063/1.352923

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Various probe diagnostic methods have been applied to rf plasmas with non‐Maxwellian electron energy distribution functions (EEDF) and the results of these diagnostic methods have been compared. Plasma density and electron temperature were obtained using standard procedures from the electron retardation region (classic Langmuir method), the ion saturation region, and the electron saturation region of the measured probeI/Vcharacteristic. Measurements were made in a 13.56‐MHz capacitive argon rf discharge at two gas pressures:p=0.03 Torr, where stochastic electron heating is dominant, andp=0.3 Torr, where collisional electron heating dominates. Thus, the measured EEDF at each gas pressure manifests a distinct departure from thermodynamic equilibrium being bi‐Maxwellian at 0.03 Torr and Druyvesteyn‐like at 0.3 Torr. Considerable differences in electron density and temperature were obtained from the different parts of the probe characteristic and these values differ dramatically in many cases from those found from integration of the measured EEDF’s, thus demonstrating that using standard procedures in non‐Maxwellian plasma can give misleading results.

ISSN:0021-8979    

DOI:10.1063/1.352924

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Magnetron discharges are widely used as sputtering sources for thin film deposition. Despite the importance of the sheath region where the electric field can be very high, there have been few experimental investigations of this region in magnetron plasmas. We report values of the sheath thickness deduced from measurements of the electric field distribution using laser spectroscopy. With this technique, a transition which is normally forbidden becomes in the presence of an electric field partially allowed so that laser induced fluorescence on this transition can be used as a measure of the electric field. It was found that the sheath thickness was approximately equal to the maximum displacement, in the absence of collisions, of a secondary electron from the cathode surface.  

ISSN:0021-8979    

DOI:10.1063/1.352925

出版商:AIP    

年代:1993

数据来源: AIP