摘要:

In an earlier paper, measurements of the electron mobility in GaAs as a function of electric field using a magnetoresistance technique were presented which revealed variations in the mobility due in part to field‐dependent scattering centers. These centers were hypothesized to be multiply ionized acceptor impurities which by their large Coulomb cross section adversely affected the electron mobility in the material. Further studies using photoconductivity techniques at liquid‐nitrogen temperatures to obtain the necessary sensitivity have shown that in the above case, acceptors, probably copper, exist in the material, and can be assumed to be the source of the observed field‐dependent effect. The relatively high purity of these materials, as evidenced by their good performance as microwave sources, indicates that the concentration of the impurity is of the order of 1012/cm3.

ISSN:0021-8979    

DOI:10.1063/1.1662548

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Theoretical as well as experimental investigations were carried out for the propagation of leaky waves along an important class of optical thin‐film waveguides. For this type of guiding structure which may consist of heteroepitaxial deposition of ZnS or ZnSe on GaAs, the dielectric constant of the thin film is less than that of the substrate. Consequently, only the leaky type of guided waves may exist. Theoretical results show that the attenuation constants of leaky modes, which may be TE or TM, are inversely proportional to (thickness of layer)3and directly proportional to (wavelength)2, and that TM modes are more lossy than TE modes. The existence of these leaky modes has also been demonstrated for three different thicknesses.

ISSN:0021-8979    

DOI:10.1063/1.1662549

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The analysis of LiH and LiD nanosecond — created laser plasmas reveals correlations between the various parameters of each plasma event. Relationships are found involving the energy spectra of the ion species, the target reflectivity, neutron production, hard and soft x‐ray emission, the electron temperature, and the input laser energy. Ion — expansion spectra of nonthermal origin are observed under the condition of high target reflectivity. High target reflectance is correlated to neutron and hard x‐ray production as well as an apparent decrease in electron thermal content for laser energies of 18–70 J. The ion — expansion spectra are obtained with mass and charge separation by the parallel electric and magnetic fields of a Thomson parabola ion analyzer. A novel feature of this device is the conversion of the analyzed ion beam to a visible image via an electron multiplier array, providing complete information on a single — shot basis. The Nd+3glass laser used in these experiments delivers up to 70 J to the target in 2.5 nsec (FWHM) pulses from a four‐amplifier system. Isolation and protection of the smaller amplifiers from amplified target feedback is accomplished by insertion of a pulsed Faraday rotator between the second and third amplifiers.

ISSN:0021-8979    

DOI:10.1063/1.1662550

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A large‐signal theory of oscillator noise is presented, which is applicable to oscillators employing active elements that can be described by a time‐dependent differential equation with a Langevin noise source. The method uses a modified quasistationary perturbation theory with an rf amplitude‐dependent perturbing noise voltage (current) source, which has been mathematically expressed in terms of the ``initial'' (preoscillation) amplitude and phase noise modulation rates. The usual requirement that this noise voltage (current) be a member of a normal random process, which results in equality of the two initial power spectra, is not invoked here. The rf amplitude dependence of the open‐circuit perturbing noise voltage (short‐circuit noise current) has been obtained from the differential equation of the active element, under the condition of sinusoidal current (voltage) excitation at the frequency at which it would normally oscillate. Upon linearizing in stochastic quantities, expanding the deterministic terms by means of Fourier series and Fourier transforming the result, a system of linear equations in the frequency domain is obtained for the noise voltages (currents) at frequencies about multiples of the excitation frequency and at the baseband frequency. In this way, most of the conversion processes in the active element can be taken into account. The Fourier transforms and power spectra of the initial modulation rates have been determined in terms of the upper‐ and lower‐sideband noise voltages (currents); they are used in the modified formulas of a quasistationary perturbation theory to obtain the AM and FM noise spectra of the oscillator output. The theory has been applied to IMPATT diode oscillators and the computed spectra have been compared with various experimental data. A good agreement between the theoretical predictions and experimental data has been found. Additional insight into IMPATT diode noise has been provided, since the above method has made it possible to separately evaluate the dependence of the AM and FM noise spectra on the rf output power of the oscillator as well as on other diode and circuit parameters. As a result, guidelines have been obtained for determining the optimum parameters of an IMPATT diode oscillator, for minimum noise.

ISSN:0021-8979    

DOI:10.1063/1.1662551

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Long‐pulse emissions characteristics of an oscillator which uses a thin‐walled tube of Nd: glass as the lasing medium are described. Slope efficiency in the single‐shot mode was 0.9%, with 70% of the energy being contained in a full divergence angle of 1.7 mrad. Single‐shot characteristics were maintained at repetition rates up to 0.2 pps in close agreement with the calculated thermal time constant. Peak output of 4.1 times the single‐shot value was obtained at 2–3 pps.

ISSN:0021-8979    

DOI:10.1063/1.1662552

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The morphology and crystallography of Co and Co(P) thin films (<500 Å), produced by electroplating, were examined by electron microscopy and diffraction. It was found that the pH of the plating solution affects phase constitution and texture as it does in thicker films. Films deposited at low pH showed appreciable proportion of fcc grains, and the hexagonal grains were oriented with their axes of easy magnetization parallel to the film plane. At high pH, the deposits were hexagonal and showed ⟨00.2⟩ fiber axis. A pH of 3 to 4 corresponded to the transition region. Phosphorus was co‐deposited with cobalt by adding hypophosphite ion to the plating solution. It acts as grain refiner, stabilizes the hexagonal phase, and randomizes the texture. An explanation of the effect of phosphorus on magnetic properties, which enables magneto‐optic recording, is suggested.

ISSN:0021-8979    

DOI:10.1063/1.1662553

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A detailed investigation of the Hall mobility has been carried out on a series of [inverted lazy s]2‐&mgr;‐thickn‐type {001}Si/{011¯2}Al2O3films. A specially designed Hall bridge pattern has been used to obtain independent measurements of mobility as a function of current direction in the plane of the film. The data show an anisotropy in the mobility of approximately 9%, with a maximum in mobility occuring along the ⟨100⟩ Si direction that is parallel to the ⟨21¯1¯0⟩ Al2O3direction in the plane of the substrate. This behavior is found to be a consequence, through the piezoresistance effect, of the anisotropic thermal contraction of Al2O3on cooling from the deposition temperature, which leads to an anisotropic thermally induced stress in the Si.

ISSN:0021-8979    

DOI:10.1063/1.1662554

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Laser‐supported detonation waves are generated with a pulsed CO2laser with energies up to 18 J, for a duration of 25 &mgr;sec and focused on solid surfaces in air. The time‐integrated spectrum in the visible and near‐uv range is found to consist mainly of N+and O+. The temperature and the electron density in the plasma are estimated to be greater than 25 000 °K and 1.5×1017/cm3, respectively, through a theoretical analysis of the air composition.

ISSN:0021-8979    

DOI:10.1063/1.1662555

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper reports on fluorescence and induced emission of Nd2O3‐doped glass ceramics.

ISSN:0021-8979    

DOI:10.1063/1.1662556

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Laser‐molecular‐beam techniques have been used to observe the hyperfine structure of molecular I2. A 5145‐Å argon laser, tuneable over 0.05 Å, is used to induce fluorescence in a molecular beam of I2. The measured width of the individual I2transitions is 3 MHz, i.e., a resolution of 5×10−9. The natural width of the lines has been estimated to be less than 800 kHz.

ISSN:0021-8979    

DOI:10.1063/1.1662557

出版商:AIP    

年代:1973

数据来源: AIP