Abstract: Mixed lanthanide-magnesium aluminates and lasers using monocrystals of these aluminates.These lasers in particular incorporate two flash lamps for longitudinally pumping a monocrystalline rod of a magnetoplumbite-aluminate emitting visible or infrared light, amplified between a mirror, a polarizing prism being used for passing to the outside of the laser the amplified light beam. The aluminate is of formula:(La.sub.1-x Tr.sub.x).sub.1-y-v Mg.sub.1-z-t Al.sub.11-u+y+2z/3 Cr.sub.u O.sub.19-t-3v/3.in which Tr represents a) at least one single trivalent substance chosen from among lanthanides, Y.sup.3+, Sc.sup.3+, or b) at least one pair of lanthanides formed from a divalent element and a trivalent element, while retaining the electrical neutrality by adding aluminium or oxygen deficiencies, or any combination of (a) and (b); x is a number such that 0.ltoreq.x<1; y and v are numbers such that 0.ltoreq.y+v.ltoreq.0.4; z and t are numbers such that 0.ltoreq.z+t<1, provided that when z=t=0, y+v is .noteq.

Abstract: The process involves producing a monocrystal from the ferroelectric compound, annealing the monocrystal and cooling the latter in a zero longitudinal temperature gradient. The apparatus comprises means for producing the monocrystal, and heating means for annealing the monocrystal in a zero temperature gradient, as well as for cooling the monocrystal in a zero longitudinal temperature gradient after annealing. The strain-free monocrystals may be used in the production of surface wave filters, modulators and optical amplifiers.

Abstract: The process involves producing a monocrystal from the ferroelectric compound, annealing the monocrystal and cooling the latter in a zero longitudinal temperature gradient. The apparatus comprises means for producing the monocrystal and heating means for annealing the monocrystal in a zero temperature gradient, as well as for cooling the monocrystal in a zero longitudinal temperature gradient after annealing. The strain-free monocrystals may be used in the production of surface wave filters, modulators and optical amplifiers.

Abstract: A device for tensioning a thin plate comprises at least two assemblies, each having tensioning means on one end of the plate and means for rotating the end about an axis perpendicular to the plane of the plate. When this axis does not pass through the center of the end, means for the transverse translation of the end are advantageously added to the assembly. The assemblies are arranged in such a way that the plate is in equilibrium under the tension effect. The device has particular application to the tensioning of a flat resistor for producing materials.