The conditions for the formation of stable volume discharges at atmospheric pressure in CO2–laser mixtures with an increased content of carbon dioxide and providing the generation of laser radiation pulses in the form of a "giant peak" with a base duration of up to 100 nanoseconds and a radiation energy of up to 1.5 J are determined. With the help of a selective resonator, a discrete rearrangement of radiation on individual vibrational–rotational transitions in the wavelength range of 9.2–10.8 μm is realized. The operation of the TEA–CO2 laser at pulse repetition frequencies up to 50 Hz is ensured.
The influence of the structure of the electrodes on the attainment of the maximum pulse repetition rates and the level of the average radiation power in TEA–N2 lasers is studied. It is shown that the use of sectioned cathodes promotes the formation of volumetric discharges at increased pulse repetition rates. The use of a cathode structure in the form of a set of pins with individual excitation of volume discharges in each gap, together with the use of preliminary ionization of gas mixtures by VUV radiation, ensures that the maximum pulse repetition rates of up to 10–12 kHz in N2:He mixtures are achieved. The maximum average radiation power of 6 W was achieved at a pulse repetition rate of 5 kHz for an N2:He mixture with an optimal component ratio of 30:730 at a total pressure of 760 Torr.
The results of an experimental investigation of the "electrical wind" as a means of convective renewal of gas mixtures in the gas–discharge gaps in CO2–laser mixtures at superatmospheric (1–12 Atm) pressures are presented. It is established that for a fixed value of the current of a unipolar corona discharge, the speed of the "electrical wind" does not depend on the pressure, but is determined by the chemical composition of the working mixture. The maximum values of the "electrical wind" velocity were achieved in pure carbon dioxide and molecular nitrogen and their values are 3.2 and 2.9 m∙s –1. In typical CO2:N2:He laser mixtures = 1:1:3 – 1:1:6 the values of the speed of the "electrical wind" are in the range from 2.5 to 1.5 m∙s –1. It is reported about the design and generation characteristics of a small–sized sealed–off metal–ceramic CO2 laser of superatmospheric pressure with an "electrical wind" operating at pulse repetition frequencies up to 25 Hz. At an operating pressure of 12 atmospheres and the excitation zone of the volumetric pump discharge V =18∙0.8∙0.8 cm3 achieved the maximum radiation energy in a pulse of 0.8 J with a duration of up to 10 nanoseconds.
There are described some constructions and generation characteristics of small–sized sealed–off metal–ceramic CO2-lasers working at super atmospheric pressures with active discharge volumes V1 =18×0.8×0.8 cm3 and V2 =7×0.8×0.8 cm3 and resonator length 20÷46 cm. The main goal of this work was determination of main interrelations between gas discharge parameters, parameters of optical resonator and laser energy per pulse and laser pulse duration. There are achieved radiation pulses with a maximum energy per pulse up to 50÷150 mJ and with minimal durations 5÷8 nanoseconds at pulse repetition rates up to 20 Hz.
There are reported about investigation results which directed to the creation of pulse-periodical CO2-laser working at super-atmospheric pressures. The main processes regulated volume discharge forming at total pressures up to 5 atmospheres and generation characteristics of CO2–laser working at pulse repetition rates up to 2 kHz are studied. Maximum average radiation power 120 W is achieved. Minimal duration of laser pulses up to 15÷20 nanosecond are realized.
Physical processes proceeding over the active electrode surfaces and their influence on a spatial plasma homogeneity of the volume discharge as well as the energy parameters and the resource of sealed-off pulse-periodical TEA-CO2 lasers have been investigated. Microstructures of the active electrode surfaces which lead to the increase of autoelectronic emission have been found to be formed under the influence of the volume discharge plasma and the products of plasma chemical reactions. The increased values of these currents initiate the formation of local channels in the cathode area of a volume discharge and initiation complete transition of volume discharge into a local one. The electrode materials, which provide the formation of stable volume discharges are determined and a maximum resource of sealed-off TEA-CO2 lasers is achieved.
The conditions of forming the spatial homogeneous volume discharges in N2:He; Xe:He, Kr:He and Ar:He mixtures at total pressures of P equals 0.5 - 1.5 Atm and at pulse repetition rates up to F equals 7 kHz are investigated. The influence of macro- and microinhomogeneities of the volume discharge plasma on the maximum pulse repetition rates and average radiation power of TEA-lasers are determined. A maximum value of the average radiation power of PAV equals 20 W on molecular nitrogen ((lambda) equals 337 nm) and PAV equals 28 W on transitions of neutral atoms of Xe ((lambda) equals 1 - 5 micrometers ) are obtained.
A convection heat removing from the discharge gap and deexcitation of metastabvle states of N2 onto the plates of the heat-exchanger was used. It is stated that the pumping energy density and the pulse repetition rate area terminated by the local discharges initiated by macroscopic inhomogeneities of the current density of the volume discharge and a repeated breakdown of the gap under the influence of mismatching voltages. Average powers of the laser radiation in molecular nitrogen up to 20 W were obtained.
The influence of plasma of the volume discharge on the microstructure of the active surfaces of electrodes and their autoemissive properties in CO2 laser mixtures at atmospheric pressure is researched. A correlation between a change in a microstructure of the electrode surfaces when the autoelectronic currents are increased is stated. It results in a formation local channels in a cathode area of the volume discharge and a resource limitation of small-sized sealed-off pulse-periodical TEA-CO2 lasers. Materials the more stable to the influence of plasma of the volume discharge providing for getting of a maximum resource (N greater than 108 of pulses) are determined.
The main regularities of formation of gas flows in laser mixtures of high pressure based on CO2:N2:He ((lambda) equals 9,3-10,7 micrometer), N2:He ((lambda) equals 337 nm) and Xe:He ((lambda) equals 1 - 5 micrometer) with the help of the 'electrical wind' are informed about. Maximum pumping rates of laser mixtures in discharge gaps up to 4 m*s-1 are obtained. In small-sized sealed-off TEA-CO2 lasers the pulse repetition rate is increased up to 50 - 70 Hz; in TEA-N2 and TEA-Xe lasers -- up to 120 - 140 Hz.
The results of systematical investigation in the field of production of the sealed-off TEA-CO2 lasers are reported. The main regularities of a stable volume discharge in CO2 laser mixture, containing the products of plasmachemical reactions are determined. Some versions of the sealed-off TEA-CO2 lasers operating at the pulse repetition rate up to 5 kHz are realized.
Algorithms were researched and evaluated for the active media chemical composition dynamic change in sealed-off pulsed-periodical TEA-carbon-dioxide lasers. These algorithms include behavior of up to 64 charged and neutral compounds. Also reported are the results of simulation of the transition to a quasi-equilibrium state of basic neutral compounds (carbon- dioxide, CO, O, O2, O3, N2, N, NO, NO2, NO3, N2O) in carbon- dioxide-laser mixtures of atmosphere pressure at the volume discharge of energy density W equals 0.1 to 0.5 J*cm-3 excitation with the pulses repetition rate F equals 102 - 104 Hz.
The change of gas mixture chemical composition and output power of the carbon-dioxide longitudinal pulse laser was investigated in glass and ceramic discharge tubes at pulse repetition frequencies up to 10 kHz. O2 efficient absorption with ceramics was established. The influence of gas addition (H2) and solid state catalyst (Pd, CuO*MnO2) on chemical composition stabilization, output power and life-time of sealed-off carbon- dioxide laser was studied.
Many applications ofthe pulsed IR-lasers are based on the irradiation selective effect on the molecular bonds ofthe chemical compounds [1-3]. In the near JR-region lasers based on the neutral inert gases atoms transitions have the most wide wavelengst set [4-5]. The practical applications of such lasers are defined by the average irradiation power level. The highest irradiation power values are achieved in the TEA-lasers with the Xe:He mixtures2-4 watts from the active volume Va =1,2 dm3 and hundreds ofrnilliwatts from V=50 cm3 [6,7]. In lasers of high pressure energy properties of the irradiation pulse and the pulses repetition rate are limited by the phenomena ofthe volume discharge degeneration to the local one, which is not applicable for the pumping purpose [6,7]. For the present time there are established mechanisms ofthe populating ofthe inert gases atoms working levels in the volume discharge plasma and main general rules of the volume discharge forming in dense gases [5-8]. The less studied questions are related with characteristic properties of the stable volume discharge forming in the pulsed-periodical regime. The present work is denoted to the study of how volume dischar ge forming conditions effects (such as pre-ionizator geometry, start ionization level, pulsed pumping generator and discharge gap properties matching ) on the volume discharge repeti tion-rate and on the average irradition power level in TEA-lasers based on Xe:He Kr:He and Ar:He mixtures.
The aim of this work was to investigate the influence of plasma-chemical reactions products, heat processes on the electrode surface, and the degree of coordination of pump pulse generator on the forming conditions of volume discharge in the working mixtures of sealed-off TEA CO2 laser. The main factors limiting the pulse repetition rate were determined. Some versions of sealed-off TEA CO2 lasers with the pulse repetition rate of 1 - 5 kHz and the pulse radiation energy of 10 - 50 mJ were realized.
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