The invention relates to a method for producing waveguides (201) from a material (202) of the KTP family comprising the following method steps: b) treating the material (202) in such a way that a periodic poling of the material (202) is achieved, c) treating the material (202) in a molten salt bath (309c), which contains rubidium ions, characterized in that the molten salt bath (309c) which contains rubidium ions in step c) satisfies the following boundary conditions: the mole fraction of rubidium nitrate (RbNO3) in the melt lies in the range of 86-90 mol % at the beginning of the treatment, the mole fraction of potassium nitrate (KNO3) in the melt lies in the range of 10-12 mol % at the beginning of the treatment, the mole fraction of barium nitrate (Ba(NO3)2) in the melt lies in the range of 0.5-1 mol % at the beginning of the treatment, the temperature of the melt lies in the range of 357-363° C. during the treatment. Thus the problem is solved, when reversing the known method steps, of achieving substantially identical diffusion depths of the ions during the ion exchange in order to produce periodically poled waveguides as free of corrugation as possible.