Patent ID: 8194308

Claim:
A method for the frequency conversion of coherent optical radiation with an adjustable wavelength, in which an output frequency of the radiation is converted by way of a two-stage non-linear optical process into a higher frequency, in that a frequency doubling is carried out in a first conversion step in a first non-linear optical crystal ( 301 , 302 ), and a sum frequency generation or a frequency doubling is carried out in a second non-linear optical crystal ( 401 , 402 ) in a second conversion step, wherein the radiation is coupled into the first non-linear optical crystal ( 301 , 302 ) such that at least one extraordinary wave of the output frequency propagates in the crystal ( 301 , 302 ), a positively birefringent crystal is used as the first non-linear optical crystal ( 301 , 302 ), in which a frequency doubling takes place with a type I phase matching from the extraordinary wave at the output frequency according to the <eeo> conversion scheme, such that an ordinary wave is generated at the doubled output frequency, and the second non-linear optical crystal ( 401 , 402 ) is selected such that a phase matching is enabled by rotation of the crystal ( 401 , 402 ) in the same spatial plane in which the first non-linear optical crystal ( 301 , 302 ) must also be rotated for phase matching.