The dynamical processes responsible for laser emission in the pulsed pumping of a transversely excited atmospheric (TEA) CO2 laser are investigated. An explanation for the formation of the giant pulse is proposed on the basis of a gain-switching mechanism in which it is assumed that with short strong-current pulses a high population inversion can be achieved prior to the onset of laser action. The kinetics of the mechanism are described by means of a set of nonlinear rate equations idealized to a four-energy-state system. With suitable initial conditions on the populations, the transient solution of these equations for the mixtures CO2–He and CO–N2–He appears to be consistent with the major features of experimental observation.
A transversely excited atmospheric TEA-CO, laser having a helical electrode configuration is described and analyzed. This laser configuration possesses a radial gain profile which naturally favors the excitation of the lowest-order mode of the resonator. Pulses of 0.7 J, having a peak power close to 1 MW, have been obtained in the fundamental mode. However, a strong diverging lens effect caused by the transverse electric discharges in the laser cavity produces a far field beam divergence twice as small as that calculated from the geometry of the resonator. This lens effect has also been used to lase with some geometrically unstable cavities. Two independent types of measurements, performed to study this lens effect, are shown to agree with a proposed theoretical model.Un laser C0,-TEA, a pression atmosphtrique et a excitation transverse, posskdant une configuration helicoldale d'tlectrodes est decrit et analyse. Cette configuration donne au laser un profil de gain radial qui favorise naturellement I'excitation du mode de plus bas ordre du resonateur. Des impulsions de 0.7 J et d'une puissance pointe de pres de 1 MW ont ttC obtenues dans le mode fondamental. Cependant, un important effet de lentille divergente provenant des dkcharges Clectriques transverses dans la cavitC laser produit dans le champ eloignt une divergence du faisceau deux fois plus petite que celle calculte d'aprts la geomttrie du rksonateur. Cet effet lentille a aussi Cte utilist pour opkrer le laser dans des configurations de cavitt instables du point de vue geometrique. Deux types d'experiences independantes rkalisees pour mesurer cet effet lentille se conforment a un modele thiorique propost.
The design parameters of a transversely excited atmospheric pressure COz laser using 1000 i 2 ballast resistors are determined from a series of energy measurements. Peak powers of the order of 1 MW/cmZ at the output window are achieved while the efficiency ranges from 3 to 5 % (+ 0.3). Improvements based on geometrical and electrical considerations are also suggested.
Passive mode-locking of a double-discharge TEA CO2 laser using SF6 as bleachable absorber has been achieved on several rot–vib transitions of the 00°1–10°0 band. Stable pulses shorter than 2 ns and having peak powers in the 100–200 MW range have been regularly obtained. The experimental conditions and operating characteristics of the laser required to achieve stability are described.
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