摘要:

The change in the refractive index at the surface of separation between two different media gives rise to the phenomena of reflection and refraction. Reflection requires that the boundary is not a geometrical surface but a thin transition layer. The depth of this layer was estimated by optical second‐harmonic generation and Raman scattering from the surface of a semiconductor superlattice. The function of the secondary electromagnetic waves excited in the medium was discussed.

ISSN:0021-8979    

DOI:10.1063/1.334462

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Stimulated rotational Raman scattering (SRRS) of a transversely excited atmosphere‐CO2laser in para‐H2was studied with a liquid‐N2‐cooled multiple‐pass cell. Line‐tunable output from 13.7 to 17.2 &mgr;m was obtained by changing CO2pump lines. Threshold pump energies required for SRRS were measured to be 0.9 and 1.5 J for the 9P(20) and 10P(20) CO2lines, respectively. Above the threshold, the Stokes output energies for the 10‐&mgr;m band pumping increased in proportion to the increase of the pump energies, while the increase of the Stokes output for the 9‐&mgr;m band pumping was limited. Para‐H2pressure dependence of the Stokes output energy showed that the Stokes gain became constant for pressures above 250 Torr at 100 K.

ISSN:0021-8979    

DOI:10.1063/1.334463

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A general transformation representative of the helical nature of the VAD (vapor‐phase axial deposition) process is presented which provides the basis for a general 3D characterization of the helical layer structure and associated properties throughout the VAD boule based upon rpm, axial growth rate, shape, and properties of the deposition surface. Graphical representations provide an illustration of the basic concept and dependencies. An analytical function for the 3D VAD refractive index profile based on completely invariant steady‐state deposition conditions is presented which properly exhibits both azimuthal and longitudinal phase dependencies; the VAD refractive index representation utilized by Okamotoetal. [Appl. Opt.20, 2314 (1981)] to predict VAD transmission characteristics is shown to be a subset of this general form. Preliminary experimental substantiation of the transformations validity for the representation of (VAD) helical layer structure is provided in the ripple characteristics of preform profiles as well as cross‐polarizer photographs. A practical application exists in extending the characterization of the deposition process such that the resultant VAD helical structure in the boule/preform/fiber is predictable and controllable. The distribution of the helical structure in the preform/fiber in fact fingerprints several aspects of the deposition process.

ISSN:0021-8979    

DOI:10.1063/1.334464

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Numerical calculations concerning transient pulse buildup processes are performed for a synchronously‐pumped mode‐locked dye laser system. Rate equations are used, including the amplified spontaneous emission (ASE) term. ASE is required to reach a stationary state. The calculated cavity length detuning characteristics are in good agreement with published observations. The observed large time‐bandwidth product and spectral width of the pulse are explained by the shift of the gain spectrum peak with population change. Inhomogeneous broadening in the active medium causes the frequency shift in the pulse.

ISSN:0021-8979    

DOI:10.1063/1.334465

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Rapidly degraded InGaAsP/InGaP double‐heterostructure lasers grown on (001)‐oriented GaAs substrates by liquid phase epitaxy have been investigated by photoluminescence topography and transmission electron microscopy. ⟨100⟩‐dark‐line defects and ⟨110⟩‐dark‐line defects are observed in the degraded region. The ⟨100⟩‐dark‐line defects correspond to interstitial type dislocation dipoles caused by recombination enhanced dislocation climb. Their origins are threading dislocations, V‐shaped dislocations, and dislocation networks. The ⟨110⟩‐dark‐line defects correspond to faulted dipoles extended from small faulted loops in the active layer, edge dipoles extended from threading dislocations, and glide dislocations. The velocities of the ⟨100⟩‐dark‐line defects are estimated by the operating time and the length of the dark lines, and are quite similar to those in rapidly degraded GaAlAs double‐heterostructure lasers.

ISSN:0021-8979    

DOI:10.1063/1.334466

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new computer‐based evaluation method is described which allows one to resolve rapid decay rates and to separate different decay mechanisms contributing to data from optical pump‐probe experiments. This computer‐fitting method is applied to the exemplary case of calculating the carrier lifetimes and quantifying different recombination processes in GaInAsP compounds observed experimentally by absorption bleaching. The carrier density is calculated by solving numerically the continuity equation in the general case of temporal, radial, and sample depth dependent generation and recombinations terms. Bleaching introduced by the pump beam is determined by using the appropriate theoretical relations and is then convolved in time and space with the probe beam to yield average bleaching values for comparison with the experimental ones. This evaluation method should also be applicable to many other pump‐probe experiments.

ISSN:0021-8979    

DOI:10.1063/1.334467

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The theory of the dynamical behavior of surface cracks which has previously been presented is here applied to the computation of the scattering of elastic waves in 3D geometry from planar cracks of a variety of shapes perpendicular to the surface of an elastic half‐space. Effects of crack size, shape, burial depth, and incoming wave frequency are illustrated. Appendices include discussions of reciprocity, simplifications in the long‐wavelength limit, the determination of model parameters from surface‐breaking criteria, results for in‐plane scattering from surface cracks in a 2D geometry, and scattering from buried and from partly closed 2D cracks.

ISSN:0021-8979    

DOI:10.1063/1.334468

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We give a potential representation to the differential equations of elastic waves propagating along the symmetric direction ofC∞anisotropic elastic bodies. The potential representation is a generalization of Lamb’s potential representation of the differential equations of isotropic elastic bodies. The generalized Lamb’s potential representation reduces the equations of motion to some two‐dimensional Helmholtz equations and constraint equations. Moreover, using the potential representation, we briefly prove the completeness of Mirsky’s solutions ofC∞anisotropic solid and hollow circular cylinders.

ISSN:0021-8979    

DOI:10.1063/1.334469

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Effects of both uniaxial tensile and compressive stresses on the magnetically induced velocity changes for 10‐MHz ultrasonic longitudinal waves were investigated in specimens of ASTM A‐36, SAE 4340, and HY‐80 steels. The magnetically induced ultrasonic velocity changes were found to exhibit characteristically different stress effects depending on the magnitude and sign, i.e., tensile or compressive, of the stress and the relative orientation between the stress and applied magnetic field . The effects of a compressive stress were particularly distinctive producing a prominent minimum in the velocity changes as a function of the applied magnetic field. The observed stress dependence of the magnetically induced velocity changes is qualitatively explained considering the effect of the stress and the magnetic field on the rotational motion of the domain magnetization caused by the propagating ultrasonic waves due to the magnetoelastic coupling.

ISSN:0021-8979    

DOI:10.1063/1.334470

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The acoustoelastic effect for surface and plate waves propagating in nonuniformly stressed media is analyzed. The theory is based on our earlier perturbation theory and normal mode technique which was used for volume waves. As with the earlier treatment, a Lagrangian description of the motion of the particles in an elastic medium is used. The results are applied to analyze the acoustoelastic effect for Rayleigh waves and Lamb waves in nonuniformly stressed media.

ISSN:0021-8979    

DOI:10.1063/1.334471

出版商:AIP    

年代:1985

数据来源: AIP