Abstract: A method for the production of Gaussian intensity distribution in the beam profile of secondary radiation generated by non-linear optical processes, particularly frequency conversion and more particularly frequency doubling of a primary radiation beam. The non-linearly generated, secondary radiation beam is non-Gaussian in profile due to the walk-off effect and has a near field path near the non-linear optical material and a transition field path interconnecting the near field path with a remote, or far, field path. A Gaussian secondary beam profile of substantially circular cross-section is produced at a finite distance from the optical material by providing an optical system in the transition path which, taken as a whole, has no divergence altering or imaging effect on the secondary radiation beam.

Abstract: The invention relates to a method and device for frequency conversion, particularly for frequency doubling and particularly of continuous fixed frequency laser radiation, of semi-monolithic design with a ring resonator consisting of a mirror and an optically non-linear crystal. The objective of the invention is to develop a generic method and a device by means of which the frequency conversion, particularly the generation of the second harmonic from continuous fixed frequency laser radiation under avoidance of the disadvantages described, with high efficiency, with markedly enhanced opto-mechanical stability and a much simplified ease of production is assured, and is met by application of an electrical voltage to an annular piezo-adjuster 103 arranged between the mirror 101 and the crystal 102.