摘要:

We report the observation of coherent emission from three rare‐earth ions in electro‐optic crystals. Oscillation is observed from Nd3+ions in Bi4Ge3O12, LiNbO3, and Ba0.75Ca0.25Nb26O at room temperature, and from Tm3+and Ho3+ions in LiNbO3at 77°K. Second‐harmonic radiation is obtained from LiNbO3:Tm3+and electric‐field modulation of threshold is observed for certain crystals of LiNbO3:Nd3+. The latter effect is believed to arise from crystal strain. The propagation angle for phase‐matched second‐harmonic generation is calculated to lie at 43° to thecaxis for both LiNbO3:Tm3+and LiNbO3:Ho3+at 77°K. Phasematched second‐harmonic generation from LiNbO3:Nd3+is not possible, since the maser line is an extraordinary wave. However, the polarization of the maser line in LiNbO3:Nd3+is appropriate for phasematched parametric frequency conversion in the near infrared. Attempts to observe such radiation were not successful due to the limited power available in the fundamental.

ISSN:0021-8979    

DOI:10.1063/1.1657047

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The transient temperature distribution produced by a surface heat source with Gaussian distribution in one dimension and of infinite extent in the other is calculated. The heated medium is a thin metallic film on a thick substrate. The transverse temperature gradient in the thin film is neglected and it is assumed that all the heat is generated in the thin film. The heat source is assumed to be a light beam. A stationary medium and one moving at constant velocity under the beam are considered. Numerical result of maximum temperature and heated area width are given for a glass and copper substrate.

ISSN:0021-8979    

DOI:10.1063/1.1657049

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The transition temperatureTcof a lead film has been determined from both the resistance along the film and from tunnel measurements of an aluminum‐aluninum‐oxide‐lead junction.Tcby resistivity was 7.214°K and from tunneling 7.208°K. The agreement indicates that tunneling measurements may be used for accurate determinations of the transition temperature.

ISSN:0021-8979    

DOI:10.1063/1.1657050

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

It is shown that the energy analysis of scattered electrons (EASE) is a useful tool when used in conjunction with the conventional LEED surface studies. It is demonstrated that the sensitivity is such that 0.02 monolayers of Cs can be detected on a Si surface. The Auger peak for K on a Ge(111) surface has been calibrated quantitatively and this calibration has been used to determine the K coverage after the overlayer was partially desorbed by heat treatments. The coverage measurements were used along with the LEED patterns to determine the surface structure.

ISSN:0021-8979    

DOI:10.1063/1.1657051

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The pinch effect or excess magnetic pressure is calculated and measured for an rf induction plasma in argon. This excess magnetic pressure (Pm), which hitherto has been overlooked in all previous investigations concerning the induction plasma, explains the reported anomalous flow behavior of the plasma torch. Theory for calculatingPmis given using a model of the plasma as a solid conductor of constant electrical conductivity. From current density and magnetic field distribution within the plasma, the local Lorentz force is evaluated, and summation across the plasma radius gives the maximumPmat the center of the peripheral discharge path. Published values for coupling efficiency and temperature profile are employed in conjunction with measured oscillator circuit parameters in order to make the calculation. The calculatedPmat the center of a 4.7 MHz, 2.5 kW argon induction plasma in a 30 mm tube is 64.5 dyn/cm2. At the center of the plasma,Pmwas measured with a cooled probe and found to be 71.5±3 dyn/cm2. AlthoughPm/P≈10−4, the magnetic pressure has an appreciable effect on the fluid mechanics of the discharge. The pinch or compressive force acts inward around the circumference, but not at the ends of the cylindrical plasma. Consequently, a magnetically induced flow occurs out from both ends of the plasma.

ISSN:0021-8979    

DOI:10.1063/1.1657052

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The integrals0∞xl(x2n+a2n)−1ex(ex±1)−2dxare evaluated in closed form in terms of the trigamma function. The casen=2,l=4, and some related integrals are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1657053

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The dc sparking potential of pure nitrogen gas has been measured under uniform electric field conditions in the pressure range 15–3000 psi(1–200 atm) and at electrode separations ranging from 0.25–25 mil (6.3–635 &mgr;). Departures from Paschen's law are found to occur at very high fields and to depend upon cathode conditions. A model is proposed in which current is field‐emitted from the cathode under the combined effect of the applied field and a positive‐ion space charge on an insulating layer at the cathode; at sufficiently high fields, the cathode current becomes unstable and breakdown results. The model predicts a relationship between an electron multiplication factor and the applied field, which is found to be consistent with the experimental results.

ISSN:0021-8979    

DOI:10.1063/1.1657054

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The gross features of previous computer results on stable accumulation and depletion layers are explained analytically. Further, the drift velocity of the accumulation plane in the singular limit,D=0, is obtained by a simple geometric construction based solely on the velocity‐field characteristic. This result is related to the drift velocity of the finite accumulation layer, at the same outside velocity, for theD≠0 case via a stringent inequality. For the general case,D=D(F), a new integral equation is derived from the starting differential equations.

ISSN:0021-8979    

DOI:10.1063/1.1657055

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The effect of strain rate on the room‐temperature strength of soda‐lime‐silica glass was determined. The strength of acid‐etched glass rods increased continuously from 190 200 to 284 800 psi on increasing the strain rate from 9×10−4to 15×10−2in./in./min. No difference in strengths was observed on testing in laboratory atmosphere or with the specimens wetted with distilled water. For abraded glass rods the strength in laboratory atmosphere varied from 12 555 to 16 540 psi on varying the strain rate from 3×10−3to 9×10−2in./in./min. Tests conducted with the abraded samples wetted with distilled water caused approximately a 10% reduction in strength, but no appreciable change in the strain‐rate sensitivity. The stress corrosion model proposed by R. J. Charles successfully predicts the room‐temperature strain‐rate sensitivity of the failure process for both acid‐etched and abraded glass samples. Using relationships derived from this model, it was further shown that the stress concentration relationship proposed by Inglis is valid for acid‐etched glass.

ISSN:0021-8979    

DOI:10.1063/1.1657056

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A method has been developed to measure thermal properties of a media from time‐dependent temperature distributions. Data from a number of locations and times are used to construct polynomial approximations to the observed phenomenon. Derivatives appearing in the differential equation describing the temperature field are evaluated from the polynomials and are then used to determine the parameters in the equations. Two examples are included. The first is a measurement of the thermal diffusivity of copper. A simple experiment is shown to give results over a range of 100°C which agree with the literature to within 3%. The second is an investigation of the space dependence of the heat generation due to nuclear radiation in a metal cylinder placed in a reactor.

ISSN:0021-8979    

DOI:10.1063/1.1657057

出版商:AIP    

年代:1969

数据来源: AIP