Patent ID: 7352505

Claim:
A device for optical frequency conversion of at least two laser beams ( 14 , 16 ) of ultra-short beam pulses which have a temporal offset and a spatial walk-off, with at least one optically non-linear medium ( 56 ), said ultra-short pulses having a duration of less than 100 ps, comprising: in the beam path before the optically non-linear medium ( 56 ) is arranged a double refracting crystal ( 54 ), the length of the double refracting crystal and the optical crystal axis of the double refracting crystal with respect to the propagation direction of the laser beam are set such that the change caused by the double refracting crystal ( 54 ) in the location and time of incidence of the beam pulses ( 14 , 16 ) on the optically non-linear medium ( 56 ), the direction of the walk-off in the double refracting crystal ( 54 ) being opposite the direction of the walk-off in the optically non-linear medium ( 56 ), and the resulting change in the spatial and temporal overlap of the beam pulses in the optically non-linear medium ( 56 ) for optical frequency conversion in the medium ( 56 ) give a conversion efficiency which is higher than the conversion efficiency which would be achieved without the double refracting crystal ( 54 ) compensating for temporal offset.