a description will now be given of the production of monocrystals by the czochralski method in an iridium crucible from mixed aluminates according to the invention and complying with the formulas given in the left - hand part of the following table . these aluminates are produced in the dry phase by mixing powders of oxides la 2 o 3 , nd 2 o 3 , mgo and al 2 o 3 . the powder quantities used are given in the left - hand part of the table . the relative quantities of the powders are determined by weighing in a two liter polyethylene bottle or flask . the starting material used can be the rhone - poulenc la 2 o 3 and nd 2 o 3 powder having respective purity levels of 99 . 999 % and 99 . 9990 %, mgo powder marketed by jmc under the name gdl with a purity level of 99 . 999 % and al 2 o 3 powder produced by criceram and marketed under the name &# 34 ; exalα &# 34 ; with a 99 . 98 % purity level . as lanthanum and neodymium oxides are very hygroscopic , it is firstly necessary to calcine them before mixing them with the alumina . this calcination takes place in an alumina crucible for 16 hours at a temperature of 1100 ° c . magnesia and alumina powders are added to the la and nd oxides calcined in the alumina crucible . this is followed by homogenization of the powder mixture by stirring for 24 h . this mixture is them compacted by isostatic compression in a diameter 70 mm latex envelope under a pressure of 2 kilobars . annealing takes place for 20 hours at 1550 ° c . in the alumina crucible . the thus obtained mixed aluminate powder is then placed in a 60 mm top , 60 mm diameter iridium crucible and , protected from the oxygen of the air , is raised to a melting point equal to 1810 ° c . in order to form a molten aluminate bath . a monocrystalline nucleus of the same composition as the molten bath cut parallel either to the crystallographic direction c , or to the direction a of the hexagonal mesh of the aluminate is then brought into contact with the liquid bath and slowly moved upwards , whilst effecting a rotary movement on itself . the pulling speed , which exceeds that of known aluminates , is 1 mm / h and the rotation speed 30 r . p . m . thus , the monocrystal is formed progressively at the end of the nucleus , as a function of the direction imposed thereon . using this pulling procedure , diameter 25 mm and length 100 mm aluminate bars were obtained . ______________________________________examples of monocrystals obtained byczochralski pullingpowder quantities in gla . sub . 2 o . sub . 3 nd . sub . 2 o . sub . 3 mgo al . sub . 2 o . sub . 3 crystal obtained______________________________________97 . 75 11 . 22 13 . 97 373 . 86 la . sub . 0 . 9 nd . sub . 0 . 1 mg . sub . 0 . 52 al . sub . 11 o . sub . 18 . 5297 . 75 11 . 22 16 . 20 373 . 86 la . sub . 0 . 9 nd . sub . 0 . 1 mg . sub . 0 . 6 al . sub . 11 o . sub . 18 . 697 . 75 11 . 22 21 . 60 373 . 86 la . sub . 0 . 9 nd . sub . 0 . 1 mg . sub . 0 . 8 al . sub . 11 o . sub . 18 . 897 . 75 11 . 22 12 . 15 373 . 86 la . sub . 0 . 9 nd . sub . 0 . 1 mg . sub . 0 . 45 al . sub . 11 o . sub . 18 . 4592 . 32 16 . 83 13 . 43 373 . 86 la . sub . 0 . 85 nd . sub . 0 . 15 mg . sub . 0 . 5 al . sub . 11 o . sub . 18 . 592 . 32 16 . 83 18 . 81 373 . 86 la . sub . 0 . 85 nd . sub . 0 . 15 mg . sub . 0 . 7 al . sub . 11 o . sub . 18 . 7______________________________________ fig1 diagrammatically shows a continuous power laser emitting in the infrared and using an aluminate monocrystal according to the invention . the emission wavelengths are 1054 , 1083 and 1320 nm . this laser comprises a laser cavity 2 containing an aluminate bar 4 according to the invention positioned perpendicular to the longitudinal axis 3 of the laser . this aluminate bar 4 is e . g . of formula a monochromatic light source 6 , such as an ionized krypton or argon laser , makes it possible to irradiate the aluminate bar 4 , via a convergent lens 7 , in order to ensure the optical pumping of bar 4 . laser cavity 2 also comprises a convergent lens 8 transforming the light emitted by the aluminate bar 4 into a parallel light beam , which is then passed onto an exit mirror 10 . following reflection on mirror 10 , the light beam again passes through the convergent lens 8 and the amplifying medium or aluminate bar 4 . the amplified laser beam is then reflected by a dichroic entrance mirror 12 , in the vicinity of which is placed bar 4 . mirror 12 is transparent to the light emitted by monochromatic source 6 and opaque to that emitted by aluminate crystal 4 . the laser beam adequately amplified in cavity 10 is then passed towards the outside of the laser , via mirror 10 , which is partly transparent to the light emitted by aluminate monocrystal 4 . the wavelength tunability can be obtained with the aid of a wavelength selection system 14 placed between convergent lens 8 and exit mirror 10 of laser cavity 2 , said system being of the brewster angle prism or interference filter type formed from two birefringent material plates . this pulsed laser comprises a cavity 4 containing a monocrystalline bar 16 of an aluminate according to the invention arranged parallel to the longitudinal axis 17 of the laser . this aluminate is e . g . of formula on either side of bar 16 are arranged high intensity , elongated , xenon flash lamps 18 , 20 , also oriented in accordance with laser axis 17 . these lamps also ensure a longitudinal optical pumping of aluminate bar 16 . laser cavity 14 also comprises a quarter - wave plate 22 which converts the linearly polarized incident light from bar 16 into a circularly polarized light . plate 22 is followed by a plane mirror 24 and a divergent convex mirror 26 . following reflection on mirror 26 the circularly polarized , adapted , widened light beam again traverses the quarter - wave plate 22 , thus producing a vertically polarized beam , which completely sweeps the amplifying medium or bar 16 , whilst extracting therefrom the maximum light energy . the amplified laser beam propagating in the direction of a concave , highly reflecting mirror 28 is interrupted by a polarizing prism 30 ejecting the vertically polarized beam 32 out of the laser cavity . a convergent lens 34 makes it possible to obtain a parallel light beam . this pulsed laser is equipped with an electrooptical switch 36 , which is more commonly known as &# 34 ; q 1 switch &# 34 ;, positioned between concave mirror 38 and exit polarizer 30 . when this switch is closed , i . e . when a voltage is applied thereto , the laser cannot operate . thus , during &# 34 ; pumping &# 34 ; the amplifying medium with lamps 18 and 20 , polarizer 30 is transparent to the horizontally polarized photons and allows light to pass to switch 36 . the latter rotates the polarization direction by 90 ° and prevents polarizer 30 from transmitting said light . conversely , on opening electrooptical switch 36 , the latter no longer impairs the horizontal polarization from the polarizer , so that the laser cavity 14 can amplify the light emitted by bar 16 . a diaphragm 38 can be placed between the switch and the polarizer for channelling the laser light . to obtain a wavelength - tunable pulsed laser , a wavelength selection device 40 , like that described hereinbefore , can be placed between plate 22 and mirror 24 . the lasers described hereinbefore have only been given in an illustrative manner and other laser types can also be equipped with an aluminate monocrystal according to the invention . the aluminate monocrystals according to the invention can be used in all applications presently employing a laser emitter of the yag type . in particular , these monocrystals can be used for lasers intended for the cutting or marking of material , as well as for producing welds . the cutting of the material is ensured by placing a monocrystalline aluminate in the cavity of a laser , as described hereinbefore , by then orienting and focusing on the surface of the material the light from the laser in order to bring said material locally to its melting point , thus ensuring its cutting as it moves in the laser beam . apart from applications of the yag type , the aluminates according to the invention have their own special applications , which are more particularly linked with the main laser emission wavelength of 1 . 054 μm . this wavelength can be used for triggering the laser effect of phosphate and fluophosphate glasses used as amplifier stages in systems for the study of controlled thermonuclear fusion according to the inertial confinement method . in the field of this particular application , the aluminate according to the invention is consequently in competition with the lithium and yttrium fluoride of formula liyf 4 , which is doped with neodymium and at present generally used .