Abstract: The invention concerns a device for generating, by interaction(s) with three or four waves from one or several incident optical radiation(s), one or several emergent radiation(s) tuneable at least in frequency. The invention is characterized in that it consists essentially of a crystal with non-linear optical property whereof the surface defines a cylindrical volume with complete revolution, or truncated on at least two opposite faces symmetrical relative to its axis of revolution, or partial on one of two said faces. Said device is particularly designed for applications in spectroscopy, remote sensing, long-distance transmission, remote guiding. The invention also concerns a method using said device.

Abstract: The synthesis in flux of KTP and its isotypes of the formula K.sub.a Rb.sub.1-a TiOP.sub.b As.sub.1-b O.sub.4 comprises:the use of the hydroxides of potassium and rubidium as flux,heating to a temperature of 600.degree. to 800.degree. C. for about 25 to 100 hours with a thermal gradient of 5.degree. to 25.degree. C./cm,the introduction of a seed crystal close to the surface of the solution, followed by the maintenance of the stage temperature or cooling at 1.degree. to 5.degree. C. per hour.

Abstract: The process of synthesis of crystals of the KTP type comprises dissolving a mixture of titanium oxide and of oxides, oxide precursors or salts of the constituents of the desired compounds or of compounds of the KTP type prepared beforehand in at least one alkali metal halide by heating at a plateau temperature of 1100.degree.-650.degree. C., cooling to a temperature close to ambient at a rate lower than about 50.degree. C./h.