摘要:

The factors affecting spark ultraviolet (UV) emission and transmission, photoionization, and photoelectron loss mechanisms in CO2TEA laser gas mixtures have been investigated and compared with the results of other workers. We found two different sources of UV radiation: N2and an unidentified emitter, postulated to be associated with ionized electrode material; C (from CO and CO2) appeared to have little effect. UV emission was directly proportional to the amount of stored electrical energy in the spark‐discharge circuit and to the cube of the peak current produced by the discharge of this energy. The uniformity of preionization produced by two kinds of spark‐free space and notched surface guided was examined and the free‐space spark was found to be superior. Photoionization was found to be due to the presence of low ionization potential (IP) alkenes in unseeded and fresh gas mixtures and also to NO and NO2in sealed devices—these were formed as a result of spark plasma reactions. The nature of the photoionization process in NO and C3H6(an alkene) was investigated; both were ionized in a single‐step process. The absorption coefficient for ionizing radiation in CO2was measured in a gas mixture containing 9% N2and a N2free mixture and values of 1.3 and 1.9 cm−1atm−1were obtained. It is thought that this may be due to changes in the spark UV emission spectrum when N2is present. The loss of photoelectrons by third body attachment to NO, NO2, and O2was monitored and only the attachment to O2was found to be significant. However, the oxides of N can play a dominant role in the subsequent negative ion reactions on a millisecond timescale.

ISSN:0021-8979    

DOI:10.1063/1.341992

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An experimental test bed has been used to extensively investigate the operating characteristics of various types of cathode and anode in an x‐ray preionizer. The temporal development, intensity, and uniformity of x‐ray beams generated by a carbon fiber cold cathode and corona plasma cathode were measured and compared. Electron densities of >108cm−3in N2(1 atm) and >109cm−3in Ar (1 atm) could be generated. Factors affecting the high repetition rate operation of both cathodes were examined. The effect of transmitting target material and thickness on x‐ray output were investigated.

ISSN:0021-8979    

DOI:10.1063/1.342478

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An experimental investigation has been conducted to determine the frequency stability of a pulsed, rf‐excited waveguide CO2laser. Unlike transversely excited atmospheric CO2lasers, for which the optical extraction of energy (laser‐induced medium perturbation) is typically the dominant source of frequency instability, the driver in the long pulse (>30 &mgr;s) waveguide laser is the thermal heating of the gain medium due to the rf input energy. Modeling of the chirp in the pulsed waveguide laser is performed. Included are both finiteV‐Teffects in the short term and heat conduction and particle migration out of the laser bore by the gaseous gain medium in the long term.

ISSN:0021-8979    

DOI:10.1063/1.341993

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Highly Bi‐substituted garnet films (BiLu)3Fe5O12(Bi=0.89/f.u.) have been grown on (111)‐oriented Gd3Ga5O12substrates by liquid‐phase epitaxy with only Bi2O3as a flux. The specific Faraday rotation &thgr;Fattains −0.14 deg/&mgr;m at 1.3 &mgr;m. Guided‐optical‐wave propagation loss of 0.6 dB/cm at 1.3 &mgr;m is obtained by doping an appropriate amount of MgO in the melt. Magnetostatic backward volume wave (MSBVW) is launched efficiently into the film as expected from the measured small ferromagnetic resonance linewidth of 0.7 Oe, whereas magnetostatic surface wave and magnetostatic forward volume wave are subject to the severe attenuation due to their coupling to spin‐wave modes. The interaction between guided optical wave and MSBVW is investigated in a transverse configuration where the input optical wave passes almost orthogonal to MSBVW. The TM‐TE optical‐mode conversion induced by MSBVW is observed over the frequency range of 3.5–7.5 GHz. Its efficiency, as high as 47%/0.8 W at 4 GHz, is obtained for the interaction length of 7 mm.

ISSN:0021-8979    

DOI:10.1063/1.341969

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A periodic system of lenses with central holes can confine and guide laser beams with small diffraction losses. In the fundamental mode an intensive part of the laser beam can be concentrated in the holes and the system may be used for high‐power beams.

ISSN:0021-8979    

DOI:10.1063/1.341970

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We analyze the nature of radiation signals detected from electrical arcing events originating on highly charged dielectric surfaces. Starting from a simple model of the arc current pulse, we calculate the electromagnetic radiation signal incident on a distant radio‐frequency receiver. The receiver is tuned to some central frequency and operates in a given bandwidth. Because the receiver responds to the arc currentderivativerather than the arc current itself, the detected radiation pulse profile can differ substantially from the current pulse profile, even when the receiver bandwidth is large compared to the reciprocal pulse width. This signal distortion significantly affects the interpretation of arc radiation data. To illustrate the point, we show that at high frequencies the detected pulse width carries very little information on the arc itself, and that even a scan of pulse width versus frequency may provide a misleading picture of possible arc dynamics. Finally, we argue that arc radiation data from radio‐frequency measurements are most useful atlowfrequencies, when the receiver frequency and bandwidth are both comparable to the reciprocal arc duration.

ISSN:0021-8979    

DOI:10.1063/1.341971

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An experiment demonstrating the propagation of a 42‐MeV electron beam from an rf linear accelerator through 1 m of H2at pressures from 10−3to 1.25 atm is reported. Measurements were made of the transmitted current and the beam’s radius, transverse position, and angular divergence along the path. The beam current was fully transmitted at all pressures, without the often detrimental plasma interactions (space‐charge neutralization, magnetic neutralization, and various plasma instabilities) seen in previous studies. The observed beam expansion was consistent with calculations of multiple scattering. The propagation can be attributed to the 4‐ps duration of the accelerator’s electron bunches. This time is three to four orders of magnitude shorter than that used in the earlier work and is shorter than the growth times for the beam‐plasma interactions. Such a beam should prove suitable for a gas‐loaded free‐electron laser.

ISSN:0021-8979    

DOI:10.1063/1.341972

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The spectra of highly ionized titanium, Tixiiithrough Tixxi, and CviLyman lines were excited in laser‐produced plasmas. The plasma was produced by uniformly irradiating spherical glass microballoons coated with thin layers of titanium and parylene. The 24‐beam Omega laser system produced short, 0.6 ns, and high intensity, 4×1014W/cm,2laser pulses at a wavelength of 351 nm. The measured wavelength for the 2p‐3sTixiiiresonance lines had an average shift of +0.023 A˚ relative to the Cviand Tixxspectral lines. No shift was found between the Cvi, Tixix, and Tixxlines. The shift is attributed to a Doppler effect, resulting from a difference of (2.6±0.2)×107cm/s in the expansion velocities of Tixixand Tixxions compared to Tixiiiions.

ISSN:0021-8979    

DOI:10.1063/1.341945

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The parametric decay of a Langmuir wave into a Langmuir wave and an ion acoustic wave is studied in a plasma slab. The coupled mode equations are solved using the perturbation technique which yields a dispersion relation for the parametric instability. The growth rate of the instability is found to increase with the width of the plasma slab and approaches the value for an infinite uniform plasma.

ISSN:0021-8979    

DOI:10.1063/1.341946

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The effect of sheath collision processes on the energy and directionality of surface bombardment in reactive ion etching is modeled. Although the methods used are generally applicable, all the numerical examples are for a low‐pressure high‐frequency oxygen plasma. Charge transfer is shown to be the dominant process controlling bombardment energies. The effect of momentum‐transfer collisions on ion bombardment energies is shown to be negligible. Equations are derived for the average energy of ions and neutrals, the average ion energy, the average neutral energy, and the ion energy distribution function. The ion drift velocity at a point in the sheath is related to the voltage distribution by an equation that provides a rigorous basis for a self‐consistent theory of the sheath voltage distribution. These equations are generally applicable to high‐frequency, low‐pressure plasmas where charge transfer is the dominant collision process. The angular distribution of energetic species is modeled using elastic scattering theory. These angular distributions can be used as input to etching models that calculate profiles and process latitudes.

ISSN:0021-8979    

DOI:10.1063/1.341947

出版商:AIP    

年代:1988

数据来源: AIP