Method and apparatus for harmonic generation of laser frequencies

Abstract

Method and apparatus 10a for the harmonic generation of laser frequencies in which an input fundamental laser beam 20 is split into two orthogonal polarisations, each polarisation being directed around an independent optical path by at least one steering element 26b, 30b, 32b, 36b, prior to a series of harmonic crystals 40, 42, to optimise conversion efficiency. Independently controlling both polarisations of the fundamental laser beam provides independent alignment optimisation of phase-matching parameters without major cross- talk / coupling with other parameters. The invention allows for a compact arrangement, spatial and temporal walk-off compensation, separate temporal adjustment between the two fundamental polarised beams for temporal compensation in the third harmonic or fifth harmonic processes, adjustment of the photon ratio, single-pulse generation, reduction of fundamental depletion for generation of the third harmonic or fifth harmonic and use of a common beam dump 16 for unconverted light 54. [Fig. 5]