摘要:

A comparison of laser performance in electron beam pumped XeF using either neon or argon diluent is presented. Extraction measurements are performed at room temperature under high‐energy loading conditions (160 kW/cm3, 1 &mgr;s laser pulse lengths) using either NF3or F2as halogen fuels. It is found with neon diluent that the laser output remains relatively constant during the excitation pulse, but with argon diluent the output increases almost linearly during the pulse. This continuous rise of the laser output with argon diluent leads to efficiencies higher than with neon diluent for input energy loadings ≳100 J/l. There are also indications that the argon diluent mixture is less susceptible to halogen burn‐up.

ISSN:0003-6951    

DOI:10.1063/1.97364

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Comprehensive measurements of the differential quantum efficiency (&eegr;d) dependence on the active layer thickness (d) for 1.55 &mgr;m InGaAsP buried crescent (BC) injection lasers are presented. The results show that &eegr;dincreases rapidly asddecreases. The strongddependence of &eegr;din 1.55 &mgr;m BC lasers suggests that a large value of optical absorption in the active region is one of the dominant mechanisms which determines the &eegr;dof these InGaAsP lasers. The likely cause for large absorption in the active region is intervalence band absorption (IBA). Thus, by reducing the active layer thickness and hence, the effect of IBA, we have obtained 1.55 &mgr;m BC lasers which exhibit threshold currents as low as 9 mA at 25 °C, &eegr;dover 45%, and high‐temperature operation up to 100 °C.

ISSN:0003-6951    

DOI:10.1063/1.97365

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The threshold current density of single quantum well (SQW) GaAs/GaAlAs lasers is calculated, taking into account the carrier populations of the confining layer. We find that these populations are significant when compared to those of the quantum well. This effect explains the better performance of the graded‐index separate confinement SQW laser when compared to the separate confinement heterostructure laser, as well as theT0performance of such lasers.

ISSN:0003-6951    

DOI:10.1063/1.97366

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A semiconductor optical‐fiber ring laser was constructed using an AlGaAs/GaAs multiple quantum well laser diode as a gain medium. The single‐mode oscillation was demonstrated and the measured spectral linewidth was less than 45 kHz. This is consistent with a theoretical calculation of its linewidth.

ISSN:0003-6951    

DOI:10.1063/1.97367

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The relative mode intensities in the hybrid CO2laser output are investigated for subthreshold operation of cw gain section. The rate equation model developed for the purpose provides estimates in very satisfactory agreement with experimental results. The model also predicts the existence of an optimum pressure and length for the cw discharge section and shows that very good longitudinal mode discrimination is possible even when cw discharge section gain is only a tenth of that required for oscillation.

ISSN:0003-6951    

DOI:10.1063/1.97368

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

This letter presents theoretical and experimental results treating the interaction between Rayleigh waves and surface‐breaking discontinuities, such as cracks and grooves, in the regime where crack depth is large compared to the Rayleigh wavelength. Particular emphasis is placed on the mode conversion to bulk waves at the crack tip. Radiation patterns are presented for both the longitudinal and shear wave contributions. The experimental data agree well with theory and show that the generation of shear waves polarized perpendicular to the crack face is particularly efficient.

ISSN:0003-6951    

DOI:10.1063/1.97369

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In this letter, we report the modification of the scanning laser acoustic microscope for the purpose of holographic and tomographic imaging. A very simple quadrature receiver is utilized to perform holographic recording of the resultant acoustic wave field. This quadrature detector mainly consists of a highpass‐lowpass circuit pair and a multiplier, and is capable of generating accurate dual reference signals. In addition to the circuit design and frequency characteristics of the filter pair, we also provide the holographic image of a range finder reconstructed by using backward propagation method to demonstrate the resolution improvement due to this modification.

ISSN:0003-6951    

DOI:10.1063/1.97370

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Bulk samples of Fe1−xNix, withxcovering the whole concentration range 0≤x≤1, have been undercooled in a containerless state by electromagnetic levitation, yielding undercooling levels not achieved to date by any other technique. Comparison with a theoretical approximation indicates that, despite the large undercoolings attained, the limit of homogeneous nucleation is not yet reached. The solidification of the undercooled melts is initiated rather by heterogeneous surface nucleation originating from surface oxidation processes.

ISSN:0003-6951    

DOI:10.1063/1.97371

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The 105‐m drop tube at NASA/Marshall Space Flight Center has been used in a series of undercooling experiments on pure metals. Ti, Zr, Nb, Mo, Rh, Hf, Ta, and Pt were undercooled 17–20% of the melting temperature in a containerless, microgravity environment. Ir and Ru were undercooled to 13%Tm. Sample sizes ranged from 175 to 880 mg.

ISSN:0003-6951    

DOI:10.1063/1.97372

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Dry sliding properties of ion beam mixed multilayered Fe‐Ti structures deposited on AISI 304 stainless steel were studied over the composition range 0–100% Ti using samples with a linearly varying composition of constituents. Our measurements revealed that a ductile surface was formed with good sliding properties over the wide composition range by ion beam mixing of deposited layers. These beneficial effects were not obtained on as‐deposited samples or by ion bombardment of either a substrate or pure iron layer deposited on a substrate. Thus, it is concluded that both the ion beam processing and composition as well as the resulting microstructure are essential for improved tribology.

ISSN:0003-6951    

DOI:10.1063/1.97373

出版商:AIP    

年代:1986

数据来源: AIP