摘要:

A computer model of the unstable‐resonator CO electric‐discharge laser is presented. The molecular kinetics model treats CO/Ar/He mixtures and includes the processes of VV and VT energy transfer, spontaneous and stimulated emission, electron collisions of the first and second kind, and one‐dimensional gas flow with heat addition. Optical propagation in the unstable resonator is treated with diffractive calculations based on the Fast Fourier Transform. An assumed initial field distribution is propagated back and forth between the mirrors of the resonator and allowed to interact with the laser medium according to a thin‐sheet gain model. These propagations are continued until successive ones yield nearly identical values for intensities, saturated gains, temperature, etc. These are the values predicted for the laser operating under the assumed conditions. The results of sample calculations are presented and discussed.

ISSN:0021-8979    

DOI:10.1063/1.325038

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Monolithic integration is described of an embedded stripe DH laser with an embedded strip waveguide of vapor‐phase‐grown GaAsP. The waveguide is composed of high‐resistivity GaAs0.9P0.1and surrounded by GaAs0.85P0.15, whose refractive index is slightly lower, to provide the optical confinement in both directions parallel and perpendicular to the guide plane. The intensity modulation of the output light was efficiently achieved by applying an electric field to the waveguide.

ISSN:0021-8979    

DOI:10.1063/1.325039

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A calculation of the effect of stripe width on the threshold current density of stripe‐geometry GaAs‐Al&khgr;Ga1−&khgr;As DH lasers is given. This calculation includes the effects of lateral current spreading, carrier out‐diffusion from the stripe, and optical mode losses. The relative importance of each of these effects is determined and threshold calculations are done for a variety of typical laser parameters such as Al content of the cladding layers, sheet resistance of the layers above the active layer, active layer thickness, and carrier diffusion length of the minority carriers in the active layer. Calculated curves for the variation of the threshold current density with stripe width and active layer thickness are compared to experimental data for a variety of types of stripe‐geometry lasers. The agreement obtained between theory and experiment is excellent in all cases.

ISSN:0021-8979    

DOI:10.1063/1.325040

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A new phenomenon that the electroabsorption of an‐p‐nheterodiode is enhanced by the absorbed light is reported. The electroabsorption is essentially based on the Franz‐Keldysh effect, where the light absorption edge of the heterodiode shifts towards a longer‐wavelength region under the applied voltage. It is shown that the optical enhancement of the electroabsorption is caused by the space charges accumulated through trapping of photogenerated free carriers.

ISSN:0021-8979    

DOI:10.1063/1.325041

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Higher‐order lateral modes produced in wide GaAs‐GaAlAs DH lasers were spectrally analyzed and photographed by the use of spatially resolved spectroscopy. These modes behave differently in mesa‐ and stripe‐geometry lasers. They were studied in detail as a function of pumping current for the mesa structure. The spacing between lateral modes could be approximated by a simple model based on a sandwich‐type symmetrical dielectric waveguide. Stripe‐geometry lasers follow Hermitian‐Gaussian mode patterns which are produced by parabolic refractive‐index profiles. An anomalous development of mode intensities near threshold was observed in the mesa diode. Immediately above threshold, higher orders dominated the near‐field patterns. Explanation for this could be found in the lateral optical gain profile produced by the interaction of the nonlinear characteristics of thep‐njunction and the geometrical series spreading resistance of the substrate.

ISSN:0021-8979    

DOI:10.1063/1.325042

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Previous models for Rayleigh‐ and Lamb‐wave electromagnetic transducers have been based on the assumption that the current distribution in each transducer conductor is uniform. We present solutions for the dynamic magnetic fields surrounding an array of flat conductors above a ground plane in which the current distribution is allowed to vary. The resulting solutions are used to calculate space‐harmonic curves and to derive a new transducer model including electrical inductance, eddy current resistance, acoustic impedance, and transducer efficiency. A direct analogy to the interdigital transducer is established. For fundamental frequency operation, this model is nearly equivalent to previous flat field models, provided the conductor width/spacing ratio is 1/2 or less. For harmonic transducer operation, the present analysis is substantially different from other models and it matches data more accurately. A method for measuring the individual insertion loss of dissimilar transducers in a lossy medium is presented.

ISSN:0021-8979    

DOI:10.1063/1.325043

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Starting with the coupled‐paraxial‐wave equations for Rayleigh waves propagating under a SAW grating, modes are derived with characteristic transverse‐mode patterns. Modes exist below the first‐order Bragg frequency both within a passband (real propagation constant) and a stop band (imaginary propagation constant). Cutoff (disappearance of guided mode solutions) is reached within the stop band above the Bragg frequency. No passband is found immediately above the stop band. Guidance of the waves by the grating is due to reflection at the grating edges and not due to a velocity difference of the Rayleigh waves between the regions outside the grating and underneath the grating. We take up the study of the effect of the velocity difference and find enhancement of guidance (as expected) when the outside region has a higher Rayleigh velocity. When the outside region has a smaller velocity, guided modes do not necessarily disappear. In fact, some guidance is provided by the velocity discontinuity.

ISSN:0021-8979    

DOI:10.1063/1.325034

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The torsional composite oscillator enables the viscosity, shear modulus, strain rate, and fluid thickness of nonelasticoviscous and elasticoviscous fluids to be determined quickly and accurately, making it a powerful technique for measuring both static and transient phenomena. In this paper the equations relating the measuredQand period to the fluid viscous properties are derived and the resulting viscosity for four nonelasticoviscous fluids from 10−3to 2 Pa s is confirmed to 1/2&percent; and better by comparison with literature values. Experimental arrangements and procedures are described which indicate how this technique can be used for strain rates from as low as ∼10−5–10−3s−1to as high as ∼105–107s−1.

ISSN:0021-8979    

DOI:10.1063/1.325035

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Convection in wall‐stabilized high‐pressure arcs is found to be highly sensitive to the relative material properties of the discharge gases. A method has been found to experimentally determine net‐radiative‐emission coefficients that are consistent with more reliably calculated electrical and thermal conductivities. The electrical conductivity of mercury arcs obtained using the electron scattering cross section for mercury derived by Rockwood gives better agreement with experimental temperature profiles than does that obtained by use of McCutchen’s cross section. Using these material properties with a theoretical convection model, good agreement was obtained with measured arc‐temperature profiles in the midplane, with the conical appearance at the bottom of the vertical arc and with the electrical properties. For 18‐mm‐i.d. walls and mercury pressures up to 13 atm, the reduction in radiation found for high mercury pressures was found to be caused by self‐absorption and not by an increase in radial thermal conduction because of turbulence or shear‐induced eddies. No evidence was found for such eddy diffusion, turbulence, or for multicellular convection.

ISSN:0021-8979    

DOI:10.1063/1.325036

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Single‐wire Fe spectra collected from two different exploded‐wire generators (Gamble II and Owl II) were analyzed to determined the ionization stages produced in the plasmas. The temperature for the hot‐plasma pinches for both generators was 1.4±0.2 keV at which an abundance of Fe XXIV transitions is produced. The FeKspectra from exploded wires are basically similar to those produced in the pinched plasma generated randomly in the vacuum spark; however, the exploded wires have lower plasma temperatures than the hottest pinches produced in the vacuum spark. A detailed interpretation of the FeLspectra formed in the exploded wires permitted line and ionization stage identifications in the 7–12‐A˚ region. Such spectroscopic data is useful for analysis of complex Fe spectra generated in multitemperature plasma devices like Tokamaks.

ISSN:0021-8979    

DOI:10.1063/1.325044

出版商:AIP    

年代:1978

数据来源: AIP