摘要:

Radiance amplification has been demonstrated in a two‐stage fluorescence radiation converter consisting of fluorescent acrylic glasses and suitably attached reflectors. The experimental results are in agreement with the theory for such systems. Internal absorption of the fluorescence radiation reduces the radiance amplification considerably. Fluorescence converter systems seem to offer some advantages in the detection of diffuse, nondirectional quantum and particle radiation and for the application of small semiconductor detectors with high sensitivity in the long‐wavelength region of the visible spectrum.

ISSN:0021-8979    

DOI:10.1063/1.1658234

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A little‐known result of Townsend and Donaldson is extended to show that, for a solenoid carrying ac or rf current, the ratio of the average applied longitudinal fieldEzto the induced azimuthal fieldE&thgr;at the periphery of the solenoid is equal to the ratio of the circumference of the solenoid to its pitch. For conventional solenoidal coils such as are used to excite electrodeless rf discharges, this ratio is typically ≳15–30. Applicability of theEz/E&thgr;ratio to the design of coils and shields is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658235

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Variance fluctuations in band‐limited vacuum‐tube flicker noise, current noise in a germanium p‐n junction, and current noise in a carbon resistor are measured by determining probability amplitude distributions of the noise signals with a multichannel pulse‐height analyzer. The variances of 30 noise specimens, each 100 sec in duration, for the three noise sources are obtained from the width of the probability amplitude distributions, all of which obey a normal‐distribution law. Fluctuations in variance are largest in the case of resistor current noise and least for current noise in a p‐n junction. Even in the latter case, however, the variations are well in excess of artifacts resulting from sampling errors, as demonstrated by examining Nyquist noise signals. It is concluded that all three 1/fnoise sources exhibit variance fluctuations to varying degrees.

ISSN:0021-8979    

DOI:10.1063/1.1658236

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The elevated‐pressure resistance behavior of differently doped samples suggests that the ratio of mobility in the [000] conduction band to that in the [100] band is constant and independent of initial mobility. A mobility ratio of 39 is indicated at atmospheric pressure. Carrier freeze‐out with respect to the [100] band was observed for S‐ and Si‐doped samples but not with Se and Te.

ISSN:0021-8979    

DOI:10.1063/1.1658237

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A He&sngbnd;Ne laser heterodyne system was utilized to evaluate the dispersive effect at 3.39 &mgr; in a He&sngbnd;He laser. The dispersion introduced by lasering atoms at 3.39 &mgr; was measured as a function of cavity loss, excitation level, and deviation of the laser frequency from line center. Theoretical and experimental results were compared, and close agreement was obtained if the natural linewidth was taken to be 115 MHz and the Doppler linewidth was taken to be 315 MHz for the 3.39‐&mgr; transition.

ISSN:0021-8979    

DOI:10.1063/1.1658238

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Output power and gain saturation characteristics are analyzed for a class of high speed flowing gas molecular lasers. Those flow lasers are treated for which laser action occurs within an optical cavity with an axis transverse to the flow direction, during the vibrational relaxation period following an initial excitation process that takes place upstream of the cavity. Performance predictions for an electrically excited fluid mixing CO2laser based upon recent experimental measurements are presented. The concept of an ``equivalent nonflow laser'' is introduced which facilitates flow laser performance analysis in certain cases.

ISSN:0021-8979    

DOI:10.1063/1.1658239

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Theoretical and experimental studies of absorber switching efficiencies are described for a ruby laser operating at 77°K. The various operating regimes of absorber‐switched lasers are reviewed and the importance of inclusion in the theory of nonsaturable losses associated with the laser and absorber media is demonstrated. A particular dye‐host combination is found to have a markedly superior switching efficiency, the essential factor being a low residual loss under saturation conditions. The residual loss of vanadium phthalocyanine is shown to be host dependent and some tentative explanations of this are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658240

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Gadolinium and yttrium dispersions were prepared in pure niobium by solidification from the melt; the size, shape, and distribution of the particles were determined metallographically. The superconducting critical temperature and critical field of niobium were unaltered by the presence of the dispersions indicating that neither gadolinium nor yttrium have measurable solubility in solid niobium. Both gadolinium and yttrium dispersions produced large hysteresis in magnetization and large critical current densities. The degree of magnetic hysteresis produced in niobium by these dispersions has only been exceeded in niobium by fast neutron irradiation. Ferromagnetic gadolinium and weakly paramagnetic yttrium appear equally effective as flux pins. It is suggested that the nature of the particle superconducting matrix interface is more important for flux pinning than the bulk magnetic properties of the dispersed phases.

ISSN:0021-8979    

DOI:10.1063/1.1658241

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A study was made of the correlation between substrate flaws and the performance of GaAs injection lasers fabricated by liquid‐phase epitaxy. These devices arep+/nstructures where thep+ region is deposited epitaxially, followed by heat treatment to displace thep‐njunction about 1–2 &mgr; into then‐type substrate. The melt‐grown substrates were studied with the aid of transmission electron microscopy, infrared transmission, x‐ray topography, etching studies, and photoluminescence. It is concluded that the dislocation density of the substrate is not the controlling factor in laser performance unless it exceeds 105cm−2. A dislocation density of 103–104cm−2is not excessive. Precipitates and impurity striations in the substrate are probably the most damaging imperfections. In Te‐doped GaAs the presence of Ga2Te3precipitates is to be avoided. In the case of Si‐doped materials, the precipitation problem appears to be less severe. Nevertheless, small clusters have been detected by electron transmission microscopy in the back portion of some melt‐grown ingots (furthest from the seed end). Their nature is unknown but they severely degrade laser performance. We show that a good correlation exists between the relative photoluminescence efficiency and laser performance. Thus, photoluminescence measurements are useful in the selection of Si‐doped substrates.

ISSN:0021-8979    

DOI:10.1063/1.1658242

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An inversion procedure for determining a domain wall profile from the associated Lorentz‐microscopy electron‐density distribution is discussed. This procedure is verified by application to computer‐simulated electron‐density distributions derived from assumed wall profiles. The experimental realization of the inversion procedure is demonstrated for high‐resolution Lorentz micrographs of films ranging in thickness from 100 to 500 Å; unreliable profiles were obtained for thicker films. The importance of correcting for the effects of nonmagnetically scattered electrons is emphasized; these effects increase with increasing sample thickness and defocussing distance. The experimental domain wall profiles exhibit first a rapid, then a slow increase of wall angle with distance from the wall center. Wall widths derived from these profiles are consistent with theoretical predictions if corrections are made for nonmagnetic scattering; if such corrections are not made, the large widths reported by other authors are obtained.

ISSN:0021-8979    

DOI:10.1063/1.1658243

出版商:AIP    

年代:1969

数据来源: AIP