摘要:

We report on direct and heterodyne detection of 70‐GHz radiation, using nonhysteretic superconductor‐insulator‐superconductor Josephson junctions with &mgr;m dimensions. The best value of noise equivalent power in the direct detection experiments was about 10−14W at 1‐Hz postdetection bandwidth and the best single sideband conversion efficiency in the heterodyne modeL−1c= −10 dB. In an experiment withL−1c= −11 dB a mixer noise temperature, including noise of the impatt local oscillator, of 2300 K is estimated.

ISSN:0021-8979    

DOI:10.1063/1.329518

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Positive light ions (He4) are extracted from a pulsed plasma source and accelerated in two states, first at constant potential and subsequently by a time varying voltage which is programmed to generate a time compressed beam bunch, downstream at a defined distance form the accelerator. Time compression of a 1‐&mgr;s extracted beam pulse into an 8‐ns bunched pulse at a distance of 66 cm from the source has been achieved. The technique provides useful applications for concentrated energy deposition on targets and is part of a proposed Light Ion Fusion Experiment (LIFE) accelerator system where 20:1 axial pulse compression would be programmed to occur during the ballistically focused and neutralized transport of intense ion beams.

ISSN:0021-8979    

DOI:10.1063/1.329519

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

We have examined the fluorescence spectra of Na2excited by Kr+(6471 A˚) and HeNe (6328 A˚) lasers in an effort to identify the optically pumped laser lines of this molecule [H. Welling and B. Wellegehausen,LaserSpectroscopyIII(Springer‐Verlag, New York, 1977), p. 365, and H. Itoh, H. Uchiki, and M. Matsuoka, Opt. Commun. 18, 271 (1976)]. For the 6471‐A˚ pump, the line positions in our fluorescence spectrum show significant systematic disagreement with the optically pumped laser lines reported by Welling and Wellegehausen; however, our transition probability calculations have been used to make proper assignments. For the 6328‐A˚ pump, in addition to the optically pumped laser lines reported by Itoh, Uchiki, and Matsuoka, we have observed some very interesting transitions which appear to be ideal wavelengths for a HeNe laser pumped Na2laser. For both cases, we have listed a number of additional wavelengths which should lase under slightly improved conditions.

ISSN:0021-8979    

DOI:10.1063/1.329520

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Results of experiments investigating the influence of resonance radiation trapping on the power and efficiency of the atomic thallium photodissociation laser are reported. Transverse pumping of a thallium iodide cell with added free metallic thallium has enabled conversion efficiencies from the ArF laser pump beam of greater than 7% to be achieved on a single Tl laser transition at &lgr; 535.0 nm. Collisional deexcitation of the 72S1/2upper laser level imposes a limit on the TlI densities which can be employed.

ISSN:0021-8979    

DOI:10.1063/1.329521

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A single‐mode AlxGa1−xAs/GaAs laser of excellent performance was made by metalorganic chemical vapor deposition. The laser has a double heterostructure with a small V‐shaped active region of a self‐aligned junction stripe geometrically grown on a groove‐etched substrate. The self‐aligning process was based on a newly found anomalous zinc diffusion phenomenon. The minimum threshold current and the maximum differential quantum efficiency in continuous operation were 15 mA and 65% for a 250‐&mgr;m‐long device. The output power up to 40 mW was attained with an Si3N4coated device. The beam shape from the laser was nearly circular with an aspect ratio less than 1.5.

ISSN:0021-8979    

DOI:10.1063/1.329522

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The performance of anx‐axis neodymium‐doped lanthanum beryllate laser (Nd:BeL) was compared to that of Nd:YAG operating as repetitivelyQ‐switched lasers. At 1 Hz, theQ‐switched outputs of Nd:BeL were twice that of Nd:YAG in rough agreement with their respective stimulated emission cross sections; however, at 10 Hz, the output with Nd:YAG was essentially constant while that of Nd:BeL fell appreciably. Analysis showed that this could be attributed to thermal lensing in Nd:BeL.

ISSN:0021-8979    

DOI:10.1063/1.329523

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The propagation of guided waves in planar optical waveguides characterized by an intensity dependent refractive index is analyzed. Closed form expressions for &Dgr;&bgr;k, the change in the propagation constant of the symmetric waveguide, were obtained using perturbation theory and were evaluated to predict optimum thickness for maximizing &Dgr;&bgr;. It is found that the maximum value of &Dgr;&bgr; is inversely proportional to the optimized thickness of the waveguide.

ISSN:0021-8979    

DOI:10.1063/1.329516

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

SiO2‐Ta2O5waveguide film exhibits a refractive index decrease up to 2% and a simultaneous film thickness increase proportional to the index decrease by CO2laser irradiation. A partial restoration to the pre‐irradiated state is observed by annealing in air at temperatures between 700 and 780 °C. The origin of the index decrease may be due to the density change with Ta2O5crystallization. For application to the optical circuit design, the effective refractive indices of the index‐decreased area are estimated, and a TE0‐TE1mode separation experiment by a 20°angle is done successfully, in order to examine the usefulness of the effective index.

ISSN:0021-8979    

DOI:10.1063/1.329517

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Multiple scattering of acoustic waves by random distribution of discrete scatterers is treated within the framework of quantum mechanical potential scattering with the use of an acoustic potential operator. The effective field approximation (EFA) and quasicrystalline approximation (QCA) are imposed on the multiple scattering equations. The use of the operator technique facilitates the introduction of coherent potential (CP). Solutions are obtained for the complex effective propagation constant in the low frequency limit for spherical scatterers. Results from the three approximations, EFA, QCA, and QCA‐CP (quasicrystalline approximation with coherent potential) are compared. Numerical results of the effective propagation velocities and the attenuation rates, as a function of the fractional volume occupied by the scatterers, are illustrated.

ISSN:0021-8979    

DOI:10.1063/1.329524

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The acoustic domains in CdS caused by the two‐step pulse are studied withEfan ultrasonic injection method and Brillouin scattering measurement. When the first‐step fieldEfis smaller than the synchronous fieldEai.e.,Ef?Ea , the factormoffm( f; frequency) of the lattice attenuation (&agr;l) increases with increasingEfand we finally obtainedm= 2 atEf=Ea. This means that the deviation fromf2.0is caused not only by the nonlinear process but also by the shock excitation. On the other hand, whenEf≳Ea, the amplitude of the current waveform decreased drastically and the maximum intensity of the frequency spectra becomes weak and it’s frequency becomes higher. This means that the nonlinear process is suppressed.

ISSN:0021-8979    

DOI:10.1063/1.329525

出版商:AIP    

年代:1981

数据来源: AIP