Determination of optimum nozzle parameters in a gasdynamic laser

In connection with the use of supersonic nozzles to create lasers, the question arises of the optimum parameters of the nozzle and the gas mixture from the aspect of obtaining the greatest population inversion of the energy levels of internal degrees of freedom of molecules of the working gas and the greatest output power of the lasers. A rather complete concept of the kinetic processes taking place during the escape of a relaxing gas mixture containing carbon dioxide through a supersonic nozzle has now been developed on the basis of calculated and experimental data. In [1–4] the problems of optimization of the parameters of a CO₂-N₂-H₂O-He mixture and of the shape of the nozzle were set up and solved in a one-dimensional steady-state formulation. The influence of the two-dimensionality of the stream in an optimum nozzle on the laser characteristics is studied in the present report. The method of through calculation suggested in [5] is used to calculate the two-dimensional flow of a relaxing gas.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 23–26, September–October, 1978.     

Energy characteristics of a carbon monoxide gasdynamic laser

The characteristics of gasdynamic lasers based on mixtures of carbon monoxide with nitrogen and inert gases were investigated and the populations of vibrational levels of CO molecules, the gain of the mixture, and the generation power were determined in [1–8]. But the parameters of a gasdynamic laser (GDL) in the optimum emission mode have not been determined up to now. The difficulties in calculating the optimum energy characteristics are connected with the complexity of the calculating model and the large number of parameters of the system. The energy characteristics of a CO gasdynamic laser are calculated and optimized in the present report on the basis of a simple model.Translated from Zhurnal Prikladnoi Mekhaniki Tekhnicheskoi Fiziki, No. 5, pp. 16–23, September–October, 1978.     

Generation of an intense molecular beam of CO2 by a gasdynamic method

The idea of using the core of a jet of expanding gas to form a molecular beam has led to the construction of complex gasdynamic facilities and has prescribed a number of specific requirements for the creation of high-intensity molecular beams. Two basic requirements are high pumping speed and a skimmer, the first element in the beam-generating system, which does not react appreciably on the jet. The present article gives the results of an experimental investigation of conditions for creating a molecular beam from a jet of carbon dioxide downstream of a sonic nozzle. The position of maximum intensity with room temperature gas in the source is given by the group of variables (P₀ ^d*)^0.4. Kn. By measuring the intensity and by mass-spectrometric analysis of a molecular beam for specific conditions we have established the CO₂ pressure in the stagnation chamber at which condensation begins. The investigations were carried out in a molecular-beam generator with cryogenic pumping.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 34–41, March–April, 1975.     

Theory of two-component gasdynamic laser

In the present paper a numerical calculation is made of the vibrational relaxation of a binary mixture of molecular nitrogen and carbon dioxide gas. The calculation is performed for the entire range of variation of the concentrations of the components and over a wide range of mixture temperatures and pressures for various geometries of the supersonic part of the nozzle (throat dimensions, degree of expansion). It is shown that population inversion of the CO₂ molecules exists within a certain range of variation of the parameters of the mixture and the nozzle. The population inversion of the vibrational levels and the gain of the gaseous mixture are calculated as functions of these parameters and of distance measured from the critical cross section of the nozzle. The energy characteristics of the two-component gasdynamic laser are optimized.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 23–30, May–June, 1974.     

Radiant energy extraction from a gasdynamic laser. Static behavior

Summary The radiant energy extraction from a gasdynamic laser has been analyzed. The considered system of energy extraction is the MOPA one, in which the flowing gas medium is used as a Power Amplifier of a Master Oscillator, a primary laser beam introduced in the gas in which an inversion has been achieved. The analysis has been performed in general terms, in order to evaluate in a simple way the effect of the beam inclination, the effect of the losses due to the collisional relaxation and to the turbulent scattering and the effect of the ratio between the primary laser flux and the maximum available laser flux in static conditions.

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Sommario S'è studiata l'estrazione di energia radiante da un laser gasdinamico. Il sistema di estrazione analizzato è quello MOPA, cioè quello in cui il mezzo è sostanzialmente usato come amplificatore, (Power Amplifier), di un fascio primario, (Master Oscillator), immesso nel gas stesso in cui è stata realizzata l'inversione delle popolazioni. Lo studio è stato condotto con criteri di generalità, al fine di valutare il più semplicemente possibile l'effetto dell'inclinazione del fascio laser sull'asse, delle perdite per diseccitazione collisionale e per la diffusione nel mezzo, l'effetto del rapporto tra flusso primario entrante e flusso totale estraibile dal gas in condizioni stazionarie.

     

Effect of flow conditions on the amplification and generation of pulsed gasdynamic lasers in N2O and CO2

The weak signal amplification is studied in jets involving N₂O-N₂He, N₂O-N₂ and CO₂-CO-N₂-He mixtures with installations combining a shock-tube and slit-throat (1.5×40 and 2.5×70 mm²) or two-dimensional wedge (=15°, A/A _* = 15) nozzles. The relationships between amplification and gasdynamic characteristics are elucidated.     

Investigation of the inverted medium of a quasi-stationary CO2 laser with pulsed excitation

The results of an investigation of the inverted medium of a quasi-stationary CO₂ laser is presented. The medium is distinguished by the fact that the time of flight of individual molecules through the discharge gaps is less than the relaxation time of the 00 °1 CO₂ laser level. The emitted power, the gain, the saturation intensity, and the gas temperature are measured. Using the experimental data, the distribution of the molecules in the vibrational and rotational states of the inverted medium is calculated. The maximum power density attained in this experimental model is 25 W/cm³. For comparison, the characteristics of a model in which cold CO₂ is added to the flow of excited nitrogen are investigated. It is shown that in this case the output power level is determined by the efficiency with which the jets are mixed.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 23–29, January–February, 1973.The authors thank V. M. Fedorov for useful discussions and A. A. Borynyak for his help with the experiments.