ISSN:0021-8979    

DOI:10.1063/1.1713875

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Buildup and decay transients were observed when polar or nonpolar liquid cells were placed within the resonator of a helium—neon laser operating in the red at 6328 Å. Similar but smaller effects were also observed with two solids. Time constants were the order of a few seconds for all materials, which suggests a thermal phenomenon, but general heating effects were ruled out by the strong localization of the phenomenon. Transverse motion of the cell by about one beam width caused new transients similar to the initial ones.It is believed that the effects are caused by absorption of the red light in the material, producing a local heating in the vicinity of the beam and a lens effect arising from the transverse gradient of refractive index. Absorptions of 10−3to 10−4parts per centimeter are sufficient to produce the effects, and are believed to be reasonable values for the materials studied. One of the most important applications may in fact be for the measurement of small absorbancies.The experiments are described, and analysis of the lens effect from absorption is given. Alternate explanations which were considered are stated briefly.

ISSN:0021-8979    

DOI:10.1063/1.1713919

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A transmission‐line analog is developed for crossed‐field space‐charge flows from the simultaneous solution of Maxwell's equations, the Lorentz force equation, and the continuity equation. A thin one‐dimensional injected beam is assumed. The resulting fifth‐degree secular equation is solved for several values of &ohgr;c/&ohgr;p. The five system waves consist of a pair of hybrid waves, a pair of near‐cyclotron waves and a near‐synchronous wave. The results indicate that noise transformers may be based on an equivalent piecewise uniform transmission line.

ISSN:0021-8979    

DOI:10.1063/1.1713930

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The saturated emission currents from uranium carbide in cesium vapor were measured for four different bath temperaturesT: 167°, 197°, 227°, and 250°C (the cesium arival rates &mgr;a, in 1019atoms/cm2, were 0.3, 1, 3, and 6, respectively). The measurements were made with a ``plasma anode'' tube at constant temperature. The plot of log&mgr;avs 1000/Twas used to extrapolate the electron emission ``S'' curves to arrival rates that differed by a factor of ten. Since calculations based on the assumption of a homogeneous surface yields unexpectedly high binding energies and surface coverages, it seems likely that some surface patchiness exists.

ISSN:0021-8979    

DOI:10.1063/1.1713862

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Electrons that are confined in a Penning discharge geometry by electric and magnetic fields are observed to gain energy from a superimposed rf field. By shaping the electrodes in the form of hyperboloids of revolution the prebreakdown motion can be accurately described by the Mathieu equation. Resonances are predicted when the frequency of the electron in the electrostatic well is a multiple of half the rf frequency. In the pressure range investigated (air at 10−2to 10−5Torr), values as low as 40‐V dc and 3‐V rf were observed at the first resonance under conditions where the Penning mechanism alone required over 400‐V dc. Between resonances the Mathieu equation predicts runaway energy gain at considerably higher values of the rf voltage, but breakdown is observed at values much lower than the prediction. The explanation is found in energy gain through collisions with gas atoms. The collision resets the phase of the motion and allows the electron to continually gain energy from the rf field. Breakdown curves are calculated for the regions between resonances and are found to agree with experiment.

ISSN:0021-8979    

DOI:10.1063/1.1713872

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An experimental study of light modulation at 16 Gc/sec, using the linear electro‐optic (Pockels) effect, has been performed. The principal result has been the demonstration of a new type of traveling‐wave‐like light modulator, which takes advantage of the fact that in crystals which have a 4¯ axis (such as KDP— potassium dihydrogen phosphate) an electric field parallel to this axis is equivalent to a field in the opposite direction if the crystal is rotated 90° about the axis. The modulator is made of a stack of crystals alternately rotated 90° with respect to one another and of a height such that the electric field changes phase by 180° in the time light takes to pass through one crystal. In this way, the electrically induced birefringence increases with optical path even though the microwave modulating field is a standing wave with no spatial variation in the direction of light propagation. For the experiments to be described, the microwave field is obtained with a multimode solid dielectric cavity efficiently driven in its TE101mode. Results on simple devices containing two and three crystals are reported, and a discussion of the general properties of this type of device is presented. In addition, the magnitude of the electro‐optic effect in KDP and ADP (ammonium dihydrogen phosphate) has been found to be the same at 16 Gc/sec, within experimental errors of 25% in ADP and 12% in KDP, as the low‐frequency clamped effect in these materials, in agreement with previous observations at 9 Gc/sec. Results concerning the variation with optical wavelength of the electro‐optic effect in these materials at 16 Gc/sec are also reported.

ISSN:0021-8979    

DOI:10.1063/1.1713882

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The characteristics of the He&sngbnd;Ne gas laser used in a new simple interferometric technique have been studied experimentally and theoretically. The interferometer has two novel features: first, the intensity of the laser itself is used to detect the fringes and second, because the intensities of the 0.63‐&mgr; (red) and 3.39‐&mgr; (infrared) laser beams are coupled, interference in the infrared can be detected by a simple photomultiplier monitoring the red beam.The system does not respond instantaneously to changes in the optical path length; experimental measurements show that when the red beam is used to follow interference in the infrared, the maximum detectable response is limited to about 3×106fringes per second. Discussion of the frequency response and the cross‐coupling between the two wavelengths leads to the conclusion that the frequency response is limited by the red channel only.Experimental details of the interferometer are described, including the application of a multipass system which, with some loss in spatial resolution, increases the sensitivity of the interferometer by at least a factor of 20.

ISSN:0021-8979    

DOI:10.1063/1.1713893

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A theory of the excitation of elastic waves arising from photoelastic coupling with light is presented. It is similar in character to the theory of optical parametric amplification in spatially extended media. Special attention is given to the self‐excited transient case. A novel form for the space—time development of the instability appears for the case in which the spatial dimensions of the interaction region are large compared to the distance traveled by an elastic wave during the illumination time. The predicted effects should be readily observable with existing giant pulse lasers.

ISSN:0021-8979    

DOI:10.1063/1.1713918

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Levitational forces exerted by spatially nonuniform ac magnetic fields on nonmagnetic conducting spheres are derived as the negative gradient of a potential function. Surfaces representing this potential for a small rigid diamagnetic sphere are used to visualize the levitational properties of several typical fields established by circular coils. Topological characteristics of these surfaces indicate that dipole fields have very shallow potential wells only for vertical and near‐vertical positions of the coil axis, and are only marginally levitational. Helmholtz and mirror fields have similar shallow potential wells. Quadrupole fields, however, have deeper potential wells in the vicinity of the central nodal point for all positions of the coil axis, and are strongly levitational. Higher‐order multipole fields can have potential wells similar to those in quadrupole fields. The description is also applicable to the levitation of nonmagnetic superconducting bodies in nonuniform ac magnetic fields.

ISSN:0021-8979    

DOI:10.1063/1.1713920

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A study has been made to determine the average duration of dc arcs in various gases at slightly higher than atmospheric pressure. These arcs were drawn between ¾‐in. copper contacts with power being supplied from a 125‐V dc generator. The experimental vessel, which contained about 1 liter volume, was provided with two liquid‐nitrogen traps through which gas was admitted and withdrawn. The gases studied were hydrogen, helium, argon, nitrogen, oxygen, and sulfur hexafluoride. It was found that in the current range studied (about 1 to 45 A) arc duration was always statistical and finite. This behavior is similar to that observed earlier for metal vapor (vacuum) arcs. For a given current, average arc duration increased for those gases in the order listed above. In the case of the latter two (O2, SF6), arc stability is believed to have been strongly affected by arc reaction products. It was concluded that for each of the gases studied, arc duration was greater than that found for a copper vapor arc at the same current, using the same generator source. It is believed that the gases blanket the cathode surface during the arc and reduce the loss of metal vapor from cathode emission sites below that occurring in the vacuum arc. There has been strong evidence in earlier work that abundant metal vapor at the arc cathode enhances arc stability.

ISSN:0021-8979    

DOI:10.1063/1.1713921

出版商:AIP    

年代:1965

数据来源: AIP