The physical nature and manifestation of several types of instabilities and fluctuation processes in the cavity of the fast-flow CO2 -laser are considered. It was established by experiment that optimal design of optical and gas-dynamic laser sections depresses totally the high frequency fluctuations and reduces low-frequency fluctuations to the level 6-10%. It was shown that inhomogeneities in the laser cavity are apt to complicate appreciably the space-temporary structure of output laser radiation. To interpret the experimental results influence of phase aberrations on the process of formation of caustics and wavefront dislocations in laser beam is considered.
Numerical simulations of self-pulsing oscillations in fast-flow laser fitted with unstable generator and multipass amplifier were performed. Possibility of the control of the depth of power modulation was shown. A number of governing parameters can be used to vary the regime of lasing in the system. Modulation of output power depending on the pumping rate was observed experimentally in fast-flow CO2 laser
D b r i e m e n t d'ktrophysique Relativiste et d e Cosmologie O b m t o i r e , 92190 Meudon, France AbsImacL Slatting from the equations of motion obeyed by fields, as they result from general approximations [they are m!ia to be of the following form [k2n(k)]+ = 0, for quasi bosons, and a similar equation for quasifermions] a lagmgian formalism is derived and, accordingly, consewed quantities are obtained. Next these fields are quantized and general expressions for the main observables are derived. Statistical mechanics of quasiparlicles then follow via the use of covariant Wigner functions.
An Isotopic Abundance Rule F. C. Frank has recently (1948) drawn attention to the exceptions to the rule requiring even-odd nuclei to have at least one even-even neighbour of greater abundance. To the exceptions which he quotes (lz9Xe, lr7Sm, l4@Sm, lgsPt, sssU) may be added ggRu, which is slightly more abundant than looRu (Ewald 1943). We should like to comment on these exceptions.The abundances of these lsotopes have almo3t certainly been enhanced by the decay, during geological time, of ,B;Tc (half-llfe 4 x lo6 years) and of lz9I, respectively.It seems likely (see Katcoff 1947) that lZgI has a sufficiently long half-life to have survived beyond the solidification of the earth's crust. Assuming that the excess la9Xe content o f the atmosphere is derived from aZgI originally in rocks which have by now suffered erosion, one can make a rough calculation of the half-life of lz8I. The value we obtain is about 4 X lo8 years, in approximate agreement with the value suggested by Katcoff. Experiments."Ru, leBXe.
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