摘要:

The simultaneous occurrence of stimulated Raman scattering and optical frequency mixing in LiIO3at kHz PRF’s (pulsed repetition frequency) has previously been investigated using a two‐mirror internal Raman configuration. These simultaneous processes produce multiple visible outputs that are selectable by rotating the LiIO3crystal. In this paper, the same simultaneous processes are investigated using a three‐mirror configuration. It is found that the three‐mirror configuration yields smaller average visible output powers, but larger peak powers, than the corresponding two‐mirror configuration.

ISSN:0021-8979    

DOI:10.1063/1.327403

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

It is possible to obtain uniform stable long‐pulse excitation (?100 &mgr;s) in gas mixtures involving highly electronegative constituents (SF6, CCl4, NF3, and I2). Such a system was used to investigate the atomic fluorine laser. In the hollow cathode, lasing on fluorine transitions in the doublet system lasted for up to 80 &mgr;s with no signs of the self‐termination as reported previously in positive‐column devices. The excitation process of the laser appears to depend heavily upon the fluorine donor utilized. For instance, a single‐step process is involved when NF3is used whereas a two‐step process is evident for SF6. The details will be discussed.

ISSN:0021-8979    

DOI:10.1063/1.327405

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

In this study three theoretical models which yield the temporal evolution of photon densities and population levels for a pulsed chemical laser are compared. The models are applied to the Cl2/HI/He chemical laser system. The simplest one is the well‐known Boltzmann equilibrium model (BEQM) which assumes instantaneous rotational equilibrium throughout the lasing period. This assumption is removed in the detailed rotational nonequilibrium model (DRNM) which follows the time development of each vib‐rotational population level separately. A third model, recently introduced by Baer, Top, and Alfassi, is an approximate rotational relaxation model (ARRM) which represents the rotational distribution in each vibrational level as a linear combination of three known functions with time‐dependent coefficients. The main conclusions are as follows: (1) The BEQM is inadequate for providing the properties of a laser operating under low and intermediate inert‐gas pressures. It can serve at most to derive an upper bound for the actual laser performance. (2) The ARRM provides very good estimates of total laser energy and efficiency as well as of more detailed properties, such as band intensities and the temporal behavior of the vibrational populations, for a wide range of pressures. (3) The use of the DRNM cannot be avoided if fine details, such as spectral distribution of output energy or rotational energy profiles, are required.

ISSN:0021-8979    

DOI:10.1063/1.327406

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The scattered radiation patterns from surface cracks irradiated by acoustic surface waves are interpreted to provide estimates of crack length and aspect ratio, geometric crack parameters needed to enable failure prediction. The technique is demonstrated for circular and elliptical cracks as small as 100 &mgr;m in depth with an accuracy of about 10%. The key features are the positions and spacing of peaks and nulls in angular frequency dependence of scattered surface wave intensity. A simple model based on optical diffraction theory is demonstrated on cracks in commercial hot‐pressed silicon nitride studied at 100 MHz and on spark‐eroded slots in commercial aluminum studied at 2–10 MHz. The results are used to calculate the stress intensity factors and to describe the direction of crack propagation for a variety of real and simulated cracks. Implications of the technique with respect to crack closure and effects of stress and time are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.327407

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The interaction of horizontally polarized shear (SH) magnetoelastic waves with drifting carriers is analyzed in a ferrite‐semiconductor hybrid structure. Wave amplification occurs when the drift velocity of carriers exceeds the phase velocity of the wave. The more magnetostatic the wave, the stronger the interaction of the wave with carriers. The imaginary part of the wave number increases linearly as the drift field (or the drift velocity of carriers) increases, is proportional to the conductivity of the semiconductor, and takes a maximum value in the vicinity of the cutoff frequency of ferrite‐air (FA) modes. These results are supported by an approximate solution for the imaginary parts of the wave numbers for the magnetoelastic surface wave interacting with a semiconductor. It is clear that elastic waves and carriers can interact through the medium of the magnetostatic surface wave by means of magnetoelastic coupling and interaction between the magnetostatic surface wave and carriers.

ISSN:0021-8979    

DOI:10.1063/1.327408

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A volumetric constitutive law for snow is developed by considering the deformation of the ice grains and grain bonds which form the porous material. The equations of equilibrium and mass conservation are applied to both the grain body and neck regions to calculate the rate of change of grain geometry and neck geometry. The matrix material, ice, is assumed to be a nonlinear viscoplastic material. Comparison with data shows excellent agreement for a wide range of initial densities and for large volumetric deformations. Calculations are also made to evaluate grain and neck deformation during compaction. The model can be applied to porous metals and foams, although the constitutive law for the matrix material would have to be altered.

ISSN:0021-8979    

DOI:10.1063/1.327394

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The electron ionization coefficients for Ar, Kr, and Xe have been measured in the lowE/Nregion [(0.5–4) ×10−16V cm2] using a drift‐tube apparatus. At low field values, the ionization coefficient was found to be anomalously large, a fact attributed to surface photoelectron emission from radiating metastables. This contribution also explains the discrepancy between earlier measurements and recent calculations based on the transport equation. The measurements were analyzed on the basis of two contributions to the ionization rate and calculations of the transport equation, yielding a revised set of inelastic cross sections which differ from earlier ones primarily in the inclusion of shape resonances.

ISSN:0021-8979    

DOI:10.1063/1.327395

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Careful measurements have been made of the ion content of air humidified by boiling water. A very sensitive cell of new design was used, having 40 parallel plates with a total area of 6.6×104cm2spaced 0.66 cm apart. A compensating cell with much smaller plates but with an identical insulator configuration was used to correct moist air conductivity data and to study insulator leakage. Results show that unexpectedly high concentrations of small ions (106–107/cm3) are present in air humidified by boiling water and that, in a closed container, a high ion concentration can be maintained for several hours after water vapor generation by boiling water has ceased.

ISSN:0021-8979    

DOI:10.1063/1.327396

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

An investigation was made of the distribution of Dy atoms and ions and iodine atoms in the central region (r/R≲0.6) of a DyI3/Hg‐arc plasma. The arc is operated horizontally; it is centered magnetically. The mercury pressure is 4.5×105N m−2, the input power 500 W, the electrode distance 37 mm, and the tube diameter is 15 mm. The temperature profile was determined from the emission of the optically thin Hg 577.0‐nm line. The side‐on emission distributions of optically thin Dy+and Dy lines, in combination with the optical absorption of Dy+resonance lines, indicate a radial depletion of dysprosium at the arc center, which can be explained by a simple model. Combination of experiments and calculations in which ambipolar diffusion is taken into account yields the distribution of Dy atoms and ions in the central region. The distribution of the iodine atoms was determined from the emission of the optically thin I 905.8‐nm line. The iodine content of the arc exceeds the dysprosium content by about an order of magnitude. The chemical composition of the arc plasma is discussed. Measurements and calculations on self‐reversed Dy lines also show that ambipolar diffusion is a dominant process.

ISSN:0021-8979    

DOI:10.1063/1.327397

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We have obtained extreme ultraviolet (XUV) spectra of plasmas created by focusing nanosecond CO2laser pulses onto massive planar targets of Al, Ti, and CH2. The instrument used to obtain these spectra was a normal incidence extreme ultraviolet spectrograph with the entrance slit removed. The concave spherical grating of such a slitless spectrograph diffracts and focuses the XUV radiation, and the resulting images are recorded on Kodak 101 film. The XUV images are therefore space resolved but time averaged over the lifetime of the plasma. The wavelength range covered in these spectra is 200–500 A˚. In this range, the emission lines of aluminum are due to transitions between the 2s22pk, 2s2pk+1, and 2pk+2configurations within the ions from Al V through Al X. For titanium plasmas, emission lines from Ti VII, Ti XI, and Ti XII have been identified. The prominent images obtained from polyethylene plasma result from 2l‐3l′ and 2l‐4l′ transitions within the C IV ion. The general morphology of the plasma expansion shows that the most highly ionized species (Al X, Ti XII) expand away from the target surface in well‐collimated cylindrical structures. These most highly ionized species also exhibit two component structures; one component expanding along the target normal and the second component expanding parallel to the incident laser direction. The images of the low‐ionization stages (Al V, Ti VII) are also cylindrical although their spatial extent is much less than the images from the high‐temperature ions and they are not as well collimated. The observations are interpreted in terms of particular temperature structures in such plasmas and the presence of self‐generated magnetic fields.

ISSN:0021-8979    

DOI:10.1063/1.327398

出版商:AIP    

年代:1980

数据来源: AIP