摘要:

The scaling characteristics of large diameter (6≤d≤12 cm) high repetition‐rate copper‐vapor lasers are investigated using a radially dependent laser‐discharge model. Results of the model are verified with experimental data obtained on several devices including an 8‐cm‐diam 100‐W copper‐vapor laser. Two effects, penetration of the applied electric field into the plasma and gas heating, which we show are the primary considerations in volumetric scaling, are discussed in detail. Thermal constriction of the discharge resulting from gas heating is prevented by plasma skin effects that allow stable performance at large diameters. These same effects are shown to explain the sequential excitation of the laser levels, resulting in both temporally and spatially dependent behavior of the laser pulse. Projections of output power and light‐pulse characteristics are made for lasers up to 12 cm in diameter.

ISSN:0021-8979    

DOI:10.1063/1.332499

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The temperature dependence of the threshold currentIthhas been measured for (GaAl)Asv‐channeled substrate inner stripe lasers emitting in the wavelength range of 781–697 nm.Ith(350 K)/Ith(300 K) is found to increase below 750 nm with decreasing wavelength in spite of the fairly large heterojunction step height &Dgr;xof 0.4. This is well explained by the model of carrier leakage due to unconfined carriers in the active layer. The calculation indicates that the threshold‐temperature sensitivity below 750 nm is almost determined by the carrier leakage in the cladding layer when &Dgr;xis smaller than ∼0.4, and it is determined by the temperature dependence of the fraction of the total electrons in the direct conduction band of the active layer when &Dgr;xis larger than ∼0.6.

ISSN:0021-8979    

DOI:10.1063/1.332500

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The performance of a pulsed D2O laser pumped longitudinally by a CO2laser and emitting at 385 &mgr;m is investigated numerically. These studies point out the limitations in pumping efficiency due to the ‘‘bottleneck’’ effect in the vibrational deexcitation of D2O. The influence of a buffer gas on the saturation behavior is discussed. The results of this numerical simulation are in good agreement with experimental measurements. Design parameters are predicted for a D2O laser system suitable for Thomson scattering diagnostics of a Tokamak plasma.

ISSN:0021-8979    

DOI:10.1063/1.332501

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A high power D2O laser, pumped by a single mode CO2laser, has been optimized to produce 1 &mgr;s pulses at 385 &mgr;m. Pump energies up to 100 J were available using ane‐beam preionized CO2amplifier at 2.5 atm. Far infrared pulse energies of 140 mJ in multimode and 40 mJ in single mode operation have been obtained from a 4‐m unstable resonator. During parametric studies the influence of operating pressure, spatially inhomogeneous pump intensity, resonator feedback as well as saturation effects have been investigated.

ISSN:0021-8979    

DOI:10.1063/1.332502

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The self‐focusing of laser pulses in a plasma is theoretically investigated for the situation in which the refractive index change is not in equilibrium with the pulse. In particular, the analysis models a CO2laser–plasma interaction experiment in which the ponderomotive and thermal conduction dominated mechanisms of self‐focusing are dominant. The moment method and the Gaussian shape ansatz are used to describe the laser pulse propagation. Threshold powers are derived for the transient self‐focusing process, which reveals that self‐focusing can occur even for times much less than the characteristic dielectric relaxation time. Because of the behavior of the pulse heating, thermal conduction dominated self‐focusing is inherently a transient phenomenon without a true steady state limit. The governing equations are also numerically solved, revealing the existence of ion acoustic waves created by the action of moving focal spots. These transversely propagating waves may be responsible for breakup or filamentation of the laser pulse.

ISSN:0021-8979    

DOI:10.1063/1.332503

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Birefringence changes induced in LiNbO3:Fe by a light beam have been measured to determine the photovoltaic characteristics such as the saturation value of space charge field, dielectric relaxation time, the probability &fgr; of creating a free electron by an absorbed photon and the mean migration lengthLof the electron. These quantities are determined for different wavelengths covering the region 400–600 nm. The product &fgr;Lthat determines the photorefractive sensitivity of the material increases with decreasing wavelength. This increase is largely due to the increase of &fgr;, the variation of the migration length being relatively small.

ISSN:0021-8979    

DOI:10.1063/1.332504

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In an elastically isotropic thin film having a free surface with a weak periodic corrugation, deposited on a semi‐infinite substrate of another elastically isotropic material, the interaction between the Love wave guided along the film and the horizontal shear bulk elastic wave propagating in the substrate is investigated for the propagation directions lying in a plane perpendicular to the film and containing the grating vector. The transport equation for the guided Love wave incorporating the effect of the coupling with the bulk elastic wave is deduced. The theory is applied to obtain the characteristics of the output coupler in which the Love wave guided along the film radiates a bulk elastic wave in the substrate as well as those of an input coupler in which a bulk elastic wave incident on the grating region of the film launches the Love wave along the film. Energy conservation principle and the reciprocity between the output and the input couplers are examined.

ISSN:0021-8979    

DOI:10.1063/1.332505

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In this paper a new approach for using acoustic measurements to evaluate residual stresses in the presence of unknown material property variation is presented. Procedures previously applied to the evaluation of stress with acoustic measurements are reviewed, and it is shown that these involve using measurements with bulk waves propagating along the normal to the surface of a plate and do not provide sufficient information to separate the influences of stress and material property variations. To overcome this fundamental limitation, an alternative theory is developed that governs the propagation of shear waves polarized horizontally with respect to the surface of a plate (SH waves), but propagating at oblique angles with respect to the surface normal. The question of separating the effects of residual stress and material properties on acoustic velocity is addressed in detail. A practical experimental procedure is developed that permits the evaluation of the in‐plane components of the principal stresses in a plate exhibiting an unknown inhomogeneous initial anisotropy caused by material texture or microstructure. The procedure is then verified experimentally using an aluminum specimen with a known residual stress state, but unknown initial anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.332506

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The unsteady flow of an incompressible fluid in distensible tubes is investigated by means of solutions of a nonlinear wave equation. The formalism applied is related to the theory of flat water waves; the propagation of impulses is described as solitons. Relations connecting parameters describing the propagation and the physical properties, respectively, are given. Various orders of approximation are compared. Dispersion relations of the linearized version are considered; flow patterns are calculated for typical cases.

ISSN:0021-8979    

DOI:10.1063/1.332507

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Electron current flow drawn off a hollow cylindrical cathode in a pinch‐reflex ion diode is observed to have a filamentary structure. Such filamentation can lead to nonuniform anode turn on and ion emission. Consequently, ion beam brightness is degraded. In this context a purely growing thermal‐resistive instability in the cathode plasma is examined. The instability causes current filamentation and grows on a time scale comparable to the electron–ion energy equilibration time. Electron inelastic collisions have a stabilizing influence on the instability.

ISSN:0021-8979    

DOI:10.1063/1.332508

出版商:AIP    

年代:1983

数据来源: AIP