Thermal blooming of continuous wave laser radiation. (GB)

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Pergamon

abstracts 4651-4659

on

Compiled

by H Kheyrandish,

Editor’s

note

this

4651-4736

University

of Salford

following indicates

I. General vacuum

science and engineering

THEORY

OF

the title of each item denotes country of origin country of origin of work (where known).

GASES

IO 4651. On constant molecular gas flow through cylindrical tubes. A note concerning the information content of CIaosing’s eouations (GE) Clausing,; equations are re-examined with rigarc) to additional informationcontent. It isshown that the product ofClausing’sfunctions n(s) and h(s) permits an interesting conclusion about the transmission probabilities of gas particles colliding with the wall at sites symmetric to the middle of the tube. (West Germany) W H Brohl and H Hartmann. Vocuuu~. 31 (2). 1981. I I7 I 18. IO 4652. On steady non-Newtonian flow with suction past an infinite porous flat plate. (GB) The flow past an infinite porous plate with constant suction and with a magnetic field B, perpendicular to the plate is investigated for a power-law fluid with a low electrical conductivity. The small parameter method is used to solve the basic equations, taking the coefficient of magnetic field x + I as a small parameter and taking the viscous heating and temperature dependent viscosity into consideration. (Egypt) M A Ahdel-Gaid et al, J Phys. 14 (2). 1981, 1733181. IO 4653. Gas dynamics at tow pressures in a vacuum microbalance. (GB) Determination of micromass changes of solid samples in a vacuum and controlled gaseous environments at different temperatures is a powerful method for studying surfaces. The weighing at low gas pressure is highly susceptible to temperature inhomogeneities which cause spurious mass changes, the phenomenon being called the thermomolecular flow elfect. This effect was explained for some time on the basis of transverse and longitudinal Knudsen forces, both related to gradient pressure, which at low pressure accompanying a thermal gradient. The problem is analyzed by the use of a BGK model and dilfuse scattering at the surface of the inner and outer cylinders. Experimental results for helium, krypton, hydrogen oxygen and carbon dioxide are reported. In all cases the Knudsen forces are seen to exhibit a maximum (volcano plots) in the transition regime. For several values of the Knudsen number (Kn) the BGK model theory is found to be in good qualitative, as well as quantitative. agreement with the experimental data. (Spain) J L Garcia Fierro, Vucuu~u, 31 (2). 1981, 79 84.

12. GASEOUS

ELECTRONICS I2

4654. Coherence characteristics (USA) The application of a single-mode coherent source is investigated. beam that is scattered by spherical water is measured to determine results indicate that a single-mode used as a coherent source for He- Ne laser. (Japan) M Yoshikawa et al, J Opr Sot

of a single-mode

GaAlAs

laser

diode.

GaAlAs semiconductor laser as a correlation of intensity of the laser particles of uniform size suspended in its use in light-beating spectroscopy. The GaAlAs semiconductor laser can be light-beating spectroscopy in place of a The

.4ru. 71 (2).

1981.

Ltd

page

The label immediately end of each abstract

IO. KINETIC

Press

I71

174.

I2 4655. Resistive stabilisation of a discharge-excited XeCI* laser. (GB) The etTect of resistive ballasting on the discharge stability of uv-preionized. discharge-excited, XeCl laser is described. It is demonstrated that the resistive ballasting of one of the transverse electrodes has a significant

of publication,

and that at the

effect on the duration and the shape of laser output pulses. Pulses of 80 ns fwhm (I20 ns foot-to-foot) with energies up to IS ml. have been observed using this technique. D C Hogan et al, J Phys D: Appl Phys, 13 (12). 1980. L225-L228. I2 4656. Demonstration of laser action and superfluorescence in CF, optically pumped by a continuously tunable CO, laser. (GB) A continuously tunable high-pressureelectron-beam-sustained CO, laser has been used to optically pump carbon tetraftuoride at low pressures and temperatures. Tuning between the 9irm R( IO) and R( 14) CO? lines laser action was observed in CF, at virtually all pump wavelengths to within the 0.1 cm- ’ bandwidth of the pump laser. and strong superfluorescence was observed at five of these wavelengths. J M Green, J Phy.s D: Appl Phys, I3 (12). 1980. 2217 2222. I2 4657. Laser-induced optogalvanic effects under prehreakdown conditions in neon. (GB) A pulsed tunable dye laser has been used to selectively perturb two metastable states ‘P, (Is, in Paschen notation) and ‘P, (Is,) in the prebreakdown phase of ionisation growth in neon. Optogalvanic signals showing a fast positive spike followed by a slow negative component were recorded and explanations are offered for each phase of the waveform. Combined with observations of temporal growth of current. these signals provide information about the magnitude of the depletion of the metastable state .‘P, (Is, in Paschen notation) and (‘P,) in the prebreakdown phase of ionization growth in neon. Optogalvanic signals saturation curves for two optogalvanic signals are compared. S P Kravis and S C Haydon, J Phys D: Appl Phys. 14 (2). 1981. 151-161. I2 4658. Thermal blooming of continuous wave laser radiation. (GB) An experimental investigation of the thermal blooming of a focused cw CO? laser beam, under cross-wind and slewing conditions. is described. Measurements of thermal blooming were made for Fresnel numbers of 5 7 and - I3 and distortion numbers up to 4 24. These results are compared with the predictions of a computer code. and are shown to be in excellent agreement. Using this code the far-field intensity profiles for infinite gaussian and annular laser beam spatial profiles have been calculated over a wide range of Fresnel and distortion number values, Using the scaling law I,,, = I/( I +a$,“), where I,,, is the decrease in peak intensity of the farfield spatial profile due to blooming and Jl,, a phase integral, these calculations yield values for CI and h of 0.0125 and 1.660, and 0.0178 and I.301 for gaussian and annular beams respectively. A T Jones and J A McMordie, J Phys D: Appl Phys, I4 (2). 1980. l63- 172. I2 4659. Level population densities and line intensities in helium discharges at intermediate pressures. (GB) A scheme for calculating populations of excited levels and intensities of spectral lines in the positive column of helium discharges at intermediate pressures (p > 5 torr) is proposed. The electron distribution obtained from the Boltzman equation is taken into account. The distribution is strongly non-Maxwellian for electrons of energy more than 19.8 eV. Concentrations of atoms on excited levels (n =2. 3. 4, 5) are obtained from balance equations for the population of those levels. The concentration of level 2’S is the highest. Theconcentration of2’S is much less than that which would exist in the case of quasithermodynamic equilibrium between levels 2’S and 2’S The population of higher levels (n > 2) is determined by excitation from levels 2’S and 2’s. For singlet levels the excitation from level 2’S is important. Population inversion is obtained between levels 3’P-3’D. 4’P-4’D, 5’S-4’P, 4’S3sP, 5’S-4’P and 5’P-4)D. (Israel) F Dothan and Y M Kagan, J Phys D: Appl Phys. 14 (2). 1981. 183-197. 271