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Experimental results obtained on the Tokamak de Varennes during a series of reproducible ohmic discharges are presented. Profiles of basic plasma parameters are constructed and compared with theoretical predictions. In particular, the measured plasma resistivity agrees with the neoclassical scaling rather than with Spitzer resistivity. The study of electron-density fluctuations indicates a linear dispersion relation with a propagation velocity of 3.0 × 104 cm s−1. Particle transport investigations are initiated, giving experimental diffusion and convection coefficients across the plasma radius for electrons and impurity ions.

This paper reports on an extensive parametric investigation of a TEA CO2 laser operated in an unstable confocal resonator. The coupling mirror diameter and the cavity magnification, M, which give the better use of the laser medium for different applications, are experimentally determined. These results are compared to the diffractional and geometrical theories of unstable resonators. It is found that, in our experimental conditions, the energy density in the focal plane of a lens depends only weakly on the value of M while the cavities having a magnification smaller than 2 are the most efficient in extracting the energy out of the lasing medium.

We have studied the plasma expansion produced when a 25 ns CO2 laser pulse is focussed onto a massive aluminium target. The maximum laser power density available was 2 × 1012 W cm−2 in a focal spot of approximately 250 μm in diameter. Charge collector measurements of the ions in the blow-off plasma indicate that an isothermal expansion model best describes the motion of the bulk of the plasma ions. Strong competing effects thus seem to inhibit the establishment of the steady-state regime expected for sufficiently long laser pulses, although faint indications of the beginnings of such a trend may be present.

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.

The isolation of a single pulse from a transversely excited atmospheric (TEA) CO2 laser, actively mode-locked by an acoustic loss modulator, is described. The single pulse selection has been achieved with the aid of a GaAs electrooptic shutter located either inside or outside the laser resonator. Pulses of 1 MW peak power and 2 ns duration have been recorded with instrument-limited precision. The availability of such pulses uncovers new possibilities for the investigation of laser–matter interactions at 10.6 μm.

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.