摘要:

Previous studies of a commerical passive gas cell Rb87frequency standard showed a strong dependence of the output frequency &ngr;Rbupon the microwave powerP&mgr;&lgr;. A major conclusion of that work was that the dependence of &ngr;RbuponP&mgr;&lgr;was due to a line inhomogeneity effect. The line inhomogeneity interpretation suggested that substituting a wall coating for the usual buffer gas would reduce the dependence uponP&mgr;&lgr;. As a part of the present work, a wall coating (a form of paraffin) was used and a reduction of this dependence by a factor of 100 was obtained. The present work has led to a more convincing theoretical demonstration of the line inhomogeneity effect. The paper discusses some of the details of the analytical procedure. There are certain major requirements that a wall coating would have to satisfy if it is to be superior to the usual buffer gas, and these are discussed in the text. The advantages demonstrated by the present work indicate that further studies are warranted to determine if an improved standard could be built based on a wall coating.

ISSN:0021-8979    

DOI:10.1063/1.328348

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Magnetization and demagnetization behaviors of ordered &bgr;′‐NiAl B2 phase are measured as a function of time under the constant applied fields by varying the electronic circuit time constant &tgr;cof magnetometer. It is clarified that the &bgr;′‐NiAl does not have magnetic after effect at room temperature. The after effect of the phase observed previously at &tgr;c=30 sec was found to be the circuit response of the measurement system. This response showed the Voigt‐Kelvin type anelastic behavior.

ISSN:0021-8979    

DOI:10.1063/1.328349

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Optical beam deflection near a heated surface was recently introduced as a method of photothermal spectroscopy. Photothermal spectroscopy (PTS) is closely related to photoacoustic spectroscopy (PAS) in its ability to measure optical properties of opaque solids and liquids. This paper develops a theory of this effect and compares this theory with extensive experimental observations. Both are in excellent agreement. The relationship between this form of PTS and PAS is explicitly developed. Applications to the measurement of thermal diffusivity of gases is described.

ISSN:0021-8979    

DOI:10.1063/1.328350

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The lateral spread of ∼100 keV recoils in Au foils has been determined by a radioactive counting technique. A uniform distribution of recoils initially moving nearly parallel to the foil surfaces was generated by (n,2n) reactions with a high‐energy neutron beam from a cyclotron. The fraction of (n,2n) activity which escapes the transverse surface is a measure of the transverse spreading of the recoils. Projected ranges were measured by orienting some of the foils perpendicular to the incident neutron beam. The experimental results are in excellent agreement with the predictions of the MARLOWE binary collision code, and indicate that the transverse range ⟨‖ x‖⟩ of ∼100 keV self‐ions in Au is approximately one‐sixth of the projected range.

ISSN:0021-8979    

DOI:10.1063/1.328351

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The cross sections are reported for the collisional excitation of the ground state of hydrogen, H2X1∑+g(v″=0), leading to vibrational excitation of all fourteenv″levels. These cross sections pertain to energetic electron collisions populating theB1∑+uandC1∏±uelectronic states which in turn radiate to theX1∑+g(v″) levels. The cross sections are in the range 10−18–10−17cm2. An estimate is made of contributions from higher states.

ISSN:0021-8979    

DOI:10.1063/1.328352

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

In order to reach the power density and total energy required for inertial confinement fusion targets using electron beams, a modular approach employing multiple diodes, plasma channel transport, and relativistic electron beam (REB) overlap is being pursued. This paper reports on an analytic study of the conversion efficiency of REB’s to ions by a combination of magnetic reflection and electrostatic reflexing of the electrons in the overlap region. The initial power density (but not total power) of the incident electron beam in this scheme is reduced by the ratio of electron beam overlap radius to final pellet radius squared, and the required power density gain in the overlap region is relaxed to unity. We find for a uniform REB energy distribution (the most probable distribution function at the overlap radius): (1) the ions cannot reach the full potential of the generator; (2) ion beam conversion efficiency remains low (∼5% in energy) and increases slowly with outer shell thickness; and (3) ion voltage remains almost constant for a wide range of generator voltages.

ISSN:0021-8979    

DOI:10.1063/1.328353

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The performance of several electron sources has been investigated and compared for generating low‐current‐density microsecond electron beams with applications to gas laser excitation. A brush cathode made with 10‐&mgr;m‐diam carbon filaments gave the best peformance among the various field emitters tested. It emitted well at fields as low as 10 kV/cm. Space‐charge‐limited flow was established in ∼60 ns and apparent gap closure velocities of 1.5 cm/&mgr;s were characteristic of this cathode. Two regimes of plasma injected diodes were investigated. First, substantial control of the diode impedence was obtained when the plasma was allowed to fill the entire anode‐cathode volume prior to application of the high‐voltage pulse; however the anode current density was found to be nonuniform with poor reproducibility from shot to shot. Second, more predictable behavior was obtained when the plasma was constrained to be on the cathode surface at the time the high‐voltage pulse was applied. In this case the time integrated anode current density was found to be uniform within ±15%. Apparent gap closure velocities as low as 2 cm/&mgr;s were measured. A description of the high‐voltage pulser and of the various plasma sources used for this experiment are also presented.

ISSN:0021-8979    

DOI:10.1063/1.328354

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The velocity distributions and state densities of metastable Ca(4s4p 3P2) atoms emerging from discharge beam sources were measured by probing the Doppler shift in laser induced fluorescence. In order to cover the widely spread distribution of the longitudinal velocity component a single‐mode dye laser was used in mode hopping technique. In this way up to 4 A˚ can be covered in steps of 182 MHz distance. The longitudinal and transverse components are sampled simultaneously. For the gasdynamic jet the transfer velocities were measured from some 10 m/s up to supersonic values. Using the transverse laser beam the absorption caused by Ca in the3P2state was tested. Absorptions up to 0.995 could be achieved in the free jet. A3P density of 7×1011cm−3is calculated. Similarly for the atomic beam 2×1010cm−3is found, the flux being 4.7×1015metastable atoms/s sr. Details of the atomic beam source for metastable atoms are given.

ISSN:0021-8979    

DOI:10.1063/1.328361

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This paper presents an electromagnetic analysis of magnetic surface wave propagation on a thick transversely magnetized YIG slab. The effect of transverse variation of wave field has been taken in account; this leads to hybridization of TE and TM modes. Using the interface model the general dispersion relation has been obtained which reduces to the well‐known limiting forms. The numerical results indicate restricted validity of the earlier analyses. Specifically, for any realistic set of parameters, the propagation of surface wave inXband can be satisfactorily described only by the present analysis.

ISSN:0021-8979    

DOI:10.1063/1.328329

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The theoretical model proposed in the paper explains the influence of an inhomogeneous laser radiation in the junction plane upon the behavior of the first derivativeI dV/dIabove threshold. These inhomogeneities are connected with the existence of lateral modes. Calculations are carried out for modes represented by trigonometric functions for a buried or mesa stripe geometry laser. The condition of constant mode gain causes an increase of the average junction voltage due to the inhomogeneity of the minority carrier concentration in the active layer. This effect is observed as the ’’unsaturated’’ junction voltage above threshold.

ISSN:0021-8979    

DOI:10.1063/1.328330

出版商:AIP    

年代:1980

数据来源: AIP