摘要:

This paper describes a study of the decomposition of pentaerythritol tetranitrate (PETN) using a high‐resolution time‐of‐flight mass spectrometer. The decomposition was induced by fracturing single crystals and by laser irradiation. In the fracture experiments, the energy input was varied from the lowest level necessary to produce smooth cleavage surfaces to high‐energy loading which produced rough conchoidal fracture surfaces. In the laser experiments, a ruby laser was used in both normal andQ‐switched modes, and again the energy input was varied. For all the various experiments, the reaction products were analyzed and reaction schemes are proposed. It is shown that low‐energy fracture causes decomposition which follows the same reaction pathway as that induced thermally, with initial failure at the RO‐NO2bond. However, high‐energy fracture results in the breaking of the C‐C bonds. Two reaction pathways were observed with the laser irradiation. The first is the normal thermal process, but evidence was also found for failure at the R‐ONO2bond. The reaction continued for several milliseconds after the end of the laser pulse, suggesting a ‘‘partial’’ ignition of the explosive. In other experiments, the conditions for laser initiation of PETN in vacuum were investigated. Explosion occurred whenQ‐switched pulses of 1 J energy were applied to a molten layer of PETN.

ISSN:0021-8979    

DOI:10.1063/1.336743

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The populations of the 46 levels belonging to the configurations 2s22p2, 2s2p3, 2p4, 2s22p3s, 2s22p3p, and 2s22p3dhave been calculated for ions in the C I isoelectronic sequence with atomic numbersZ=18, 22, 26, 30, 34, and 36 and for electron densities from 1015to 1022cm−3. The populations of the 2s22p3plevels are relatively large owing to the large electron collisional monopole excitation rates from the ground configuration and to the small radiative decay rates to the ground configuration. This results in population inversions for transitions of the type 3s–3p. The gain coefficients for these transitions are determined and are compared to previous calculations. At high electron densities where collisional mixing of the excited levels becomes important, the intensities of the x‐ray transitions from the 2s22p3plevels to the 2s2p3levels decrease relative to the x‐ray transitions from the 2s22p3sand 2s22p3dlevels. The density dependence of these x‐ray line ratios is also presented. These line ratios represent a promising diagnostic for electron density.

ISSN:0021-8979    

DOI:10.1063/1.336695

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In optical communication systems operating near the zero‐dispersion wavelength of the fiber, the wavelength of semiconductor lasers should remain stabilized to minimize the effects of fiber dispersion. We analyze theoretically the requirements for mode stabilization when external dispersive feedback is used to select a longitudinal mode. The feedback bandwidth should be less than the external‐cavity mode spacing to avoid the excitation of side modes corresponding to the longitudinal modes of the external cavity. By a suitable choice of laser parameters, a multimode laser can remain stabilized in the vicinity of the feedback‐selected wavelength even when the free‐running wavelength has drifted by more than 10 nm.

ISSN:0021-8979    

DOI:10.1063/1.336696

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Stimulated emission of bremsstrahlung radiation by electrons in high Rydberg states is analyzed theoretically. This approach to bremsstrahlung masers is shown to overcome some of the previous difficulties in realizing a practical value for the bremsstrahlung gain in the millimeter‐wave regime by allowing volumetric production of monoenergetic electrons within a time period which is short compared to the thermalization time of the electron energy distribution, and by relaxing the criteria on the energy dependence of the collision cross section for achieving a positive bremsstrahlung gain coefficient.

ISSN:0021-8979    

DOI:10.1063/1.336697

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The dependence of the laser output power on the flow velocity at a cavity for a compact chemical oxygen–iodine laser is reported. The flow velocity is changed by using two vacuum pumps (3000 and 15 000l/min). It becomes experimentally clear that the laser output power is proportional to the flow velocity and the extractable O2(1&Dgr;) concentration. Output power in excess of 100 W has been extracted efficiently. The maximum overall reaction efficiency of 16.8% with the chlorine flow rate of 413 mmol/min is obtained.

ISSN:0021-8979    

DOI:10.1063/1.336698

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

It is shown that the calculated gain spectrum of the radiation generated by a two‐photon process, evaluated from a high‐order approximation solution of the wave equation, is larger than the one obtained from a zero‐order approximation. The difference between the two approximations becomes very important when the ratio of the frequency of the generated radiation to that of a focused pump is large and/or when the pump power is low.

ISSN:0021-8979    

DOI:10.1063/1.336699

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Thermal particle detection is a new approach to the detection of generic particulate contaminants on products. The method takes advantage of the low thermal conductivity of a particle/substrate interface by using rapid thermal heating to raise the particle temperature over the temperature of its surroundings. The perturbed particle is then detected by its subsequent thermal emissions with a highly sensitive IR detector. The physics of particle heating and detection both in vacuum and in air is described.

ISSN:0021-8979    

DOI:10.1063/1.336700

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Correlation photoacoustics detected from the unilluminated surface of a sample have been studied to detect well‐characterized surface grooves and subsurface inhomogeneities in nickel. The correlation image of a line scan across an opaque sample by transmission technique can present the information on the surface or subsurface characteristics of the sample. This method is especially advantageous to detect subsurface grooves or inhomogeneities which exist anywhere in an optically opaque solid because the photoacoustic signals depend on the thermal and geometrical features in the transmission process of thermal waves. The system developed makes it possible to measure the impulse response of unstable samples because of the short time taken to collect data.

ISSN:0021-8979    

DOI:10.1063/1.336701

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Metallic Faraday shields commonly in use in many ion cyclotron resonance heating experiments have been shown to have two adverse effects on the antenna‐plasma coupling properties: magnetic shielding of the antenna current and possibly significant ohmic losses. The purpose of this paper is to investigate these two effects for shields of finite thickness using a detailed analysis of the fringing fields induced by the Faraday shields. Naturally, the extension to finite thickness introduces the question of shield cross‐section shape. Considerable attention is given to this point through two case studies of a square‐edged and a rounded‐edge shield. It is shown that magnetic shielding properties of a given cross section can be characterized by a single parameter, dependent only on cross‐section shape and dimensions. Ohmic losses are seen to be 30%–40% less for a cross section with rounded edges than for the square‐edged cross section. Also of interest is a minimum in the ohmic loss versus thickness relation for the round cross section, indicating the existence of an optimum ohmic loss design with respect to shield thickness.

ISSN:0021-8979    

DOI:10.1063/1.336702

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The production of soft x rays in the plasma of a spherical pinch is estimated, using the simple concepts of Bernstein and Comisar. It is shown that a relatively minor modification of the spherical pinch dynamics is required to account for the effect of radiation loss on the behavior of the plasma. The various time constants governing the plasma are examined and it is shown that of these, the confinement or ‘‘bounce’’ time, the radiation decay time, and the electron‐ion equilibration time are the most important. A computer program has been developed which shows that, to retain most of the energy of the discharge in the electrons and thereby maximize the x‐ray exposure, it is important to choose the correct time relationship between the central spark and the peripheral inductive discharge of the pinch.

ISSN:0021-8979    

DOI:10.1063/1.336703

出版商:AIP    

年代:1986

数据来源: AIP