摘要:

We have performed single photon detection experiments at 1.3 &mgr;m and measured the error ratere. This quantity is relevant for the possible use of such a detector as a quantum limited lightwave receiver. We have also determined the dependence ofreon the quantum efficiency &eegr;.

ISSN:0003-6951    

DOI:10.1063/1.94864

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Subwave length‐resolution optical image recording is demonstrated by moving an extremely narrow aperture along a test object equipped with fine‐line structures. Details of 25‐nm size can be recognized using 488‐nm radiation. The result indicates a resolving power of at least &lgr;/20 which is to be compared with the values of &lgr;/2.3 obtainable in conventional optical microscopy.

ISSN:0003-6951    

DOI:10.1063/1.94865

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Data are presented demonstrating room‐temperature operation of a strained‐layer quantum‐well injection laser. The laser structure, grown by molecular beam epitaxy, consists of an active region with three InxGa1−xAs (x∼0.35) quantum wells (LZ∼40 A˚) separated by two GaAs barriers (LB∼30 A˚). These layers are centered in a larger GaAs collection/confinement region (LZ∼1600 A˚) bounded by AlyGa1−yAs ( y∼0.45) cladding layers. The lasers operate at &lgr;∼1.0 &mgr;m with greater than 4‐mW optical power output/facet under pulsed conditions at 300 K. Threshold current densities between 1000 and 2000 A/cm2are obtained.

ISSN:0003-6951    

DOI:10.1063/1.94866

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Shorter switching times in liquid crystal devices are traditionally achieved by raising the switching voltage. However, one of the limitations in multiplexing the boundary layer display is the necessity to keep the rms switching voltageVson the not‐yet‐selected pels below a critical threshold voltageVththat would hold them in an asymmetric state and prevent switching. By using a periodic square wave to simulate a sequence of bipolar switching pulses, we show that their orienting effect in a ‘‘dual‐frequency’’ liquid crystal can be prevented by simultaneously applying a voltage at a higher frequency where the dielectric anisotropy is negative. This permitsVs>Vth, and in principle allows faster multiplexing. The goal of increased speed was not achieved in our simulation experiment due to the inherently slow response of the dual‐frequency material used. Nevertheless, the demonstrated scheme will be advantageous when faster dual‐frequency materials are developed.

ISSN:0003-6951    

DOI:10.1063/1.94867

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A spectral linewidth of <7×10−4A and diffraction‐limited beam divergence has been obtained from a long pulse, electric discharge xenon chloride laser with intracavity Fabry–Perot etalons. A gain duration of 100 ns provided for multipass operation of the etalons, significantly improving both contrast and finesse. The electrical discharge circuit required to produce this long gain duration was comprised of a pulse forming network, saturable inductor magnetic switch, and a tapered, constant impedance, interface transmission line.

ISSN:0003-6951    

DOI:10.1063/1.94868

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

High‐energy electrons emit resonant electromagnetic radiation when passing through a spatially periodic medium. It is conventionally assumed that ultrarelativistic electron beams are required to obtain significant emission. We demonstrate theoretically the feasibility of exploiting solid‐state superlattices with short spatial periods to obtain both spontaneous and stimulated emission in the extreme‐ultraviolet and soft x‐ray range using nonrelativistic beams.

ISSN:0003-6951    

DOI:10.1063/1.94869

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A comparative study of the laser produced plasma (LPP) in vacuum at the surface of transparent crystalline &agr;‐Al2O3(sapphire) and Al metal generated by 248‐nm excimer laser pulses of 15‐ns duration is reported. It was found that the threshold fluence for strong LPP emission in sapphire is 0.55 J/cm2, which is significantly lower than that needed for the same process in clean Al (1.7 J/cm2). At fluences higher than 4 J/cm2the LPP emission from both targets is similar. The results obtained in sapphire require that its absorption coefficient increase by many orders of magnitude during the laser pulse. A possible explanation for the observed threshold difference is that the greater thermal diffusivity of Al more than compensates for its greater volatility; hence, a greater fluence is necessary to create the LPP in Al.

ISSN:0003-6951    

DOI:10.1063/1.94870

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Experimental evidence is presented indicating that a nonthermal electron energy distribution occurs in a collapsing gas shellZpinch at the time of pinch. It is estimated that these results can be explained if less than 10% of the current is associated with an energetic (∼4 keV) electron beam. Interpreting the spectroscopic diagnostics consistently with the nonthermal electron energy distribution indicates that the temperature of the plasma ‘‘hot spots’’ could be as low as ∼400 eV instead of the 1 keV obtained by assuming a thermal distribution.

ISSN:0003-6951    

DOI:10.1063/1.94863

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

In spite of the technical interest in the Hf‐N system the form of the phase diagram is not yet clear, and therefore it is difficult to predict the phase composition of thin films. In this letter Hf‐N films have been prepared by reactive dc planar magnetron sputtering and the phase composition of the films investigated by x‐ray diffraction. Between the &agr;‐Hf and HfN single phase regions a multiphase region was found consisting of &agr;‐Hf, &egr;‐Hf3N2, and/or &zgr;‐Hf4N3and also HfN in the nitrogen rich part. For the mononitride a lattice parameter of 4.54 A˚ was found which is slightly higher than reported bulk vlaues. This deviation is caused by intrinsic stresses in the films. If the nitrogen content is increased above that of the mononitride, the (111) interplanar distance increases further while all other interplanar distances decrease. At still higher nitrogen contents new reflections start to appear indicating a new phase. In this region the films also change from being conducting and nontransparent to electrically insulating and transparent.

ISSN:0003-6951    

DOI:10.1063/1.94871

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The critical volume fraction of percolation in conductivity has been determined for di‐phasic Ge films. Unlike Si, two values were found, 0.15 and 0.4, corresponding respectively to low and high substrate temperatures. Furthermore, scanning electron microscopy revealed a random spherical growth for the former value as contrast to an essentially columnar growth for the latter. The higher and lower values are consistent with the theoretical limits for two‐ and three‐dimensional percolation.

ISSN:0003-6951    

DOI:10.1063/1.94872

出版商:AIP    

年代:1984

数据来源: AIP