Device and method for converting an optical frequency

Method 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, and in at least one optically non-linear medium (56) undergo a non-linear frequency conversion, said ultra-short pulses having a duration of less than 100 ps, characterized in that before the optically non-linear medium (56) is arranged a double refracting crystal (54), the length of which and the orientation of the optical crystal axis of which 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 is achieved without the double refracting crystal (54) compensating for temporal offset.

Use of a double refracting crystal (54) in 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, and which generate a frequency conversion in at least one optically non-linear medium (56), said ultra-short pulses having a duration of less than 100 ps, wherein the double refracting crystal (54) is arranged in the beam path before an optically non-linear medium (56) such that its length and the orientation of its optically active crystal axis relative to the propagation direction of the laser beams (14, 16) are 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 crystal (56) give a conversion efficiency which is higher than the conversion efficiency which is achieved without the double refracting crystal (54) compensating for temporal offset.

A device for optical frequency conversion, comprising:

• an optically non-linear medium (56) introducing a spatial walk-off and a temporal offset into at least one of at least two pulsed laser beams (14, 16) passing through said optically non-linear medium;
• and a double refracting crystal (54) positioned in front of said optically non-linear medium (56), said double refracting crystal (54) having a length and being positioned relative to the optically non-linear medium (56) to introduce a spatial walk off and temporal offset into the said at least one of the two laser beams, said temporal offset and said spatial walk-off being opposite said temporal offset and said spatial walk-off introduced by said optically non-linear medium and being sufficient to cause said two pulsed laser beams to intersect temporally and spatially at a point within said optically non-linear medium (56).

A method of implementing an optical frequency converter, comprising:

• introducing a spatial walk-off and a temporal offset into at least one of at least two pulsed laser beams (14, 16) by passing said at least two laser beams through an optically non-linear medium (56);
• and
• prior to introducing said spatial walk-off and said temporal offset by passing said at least two laser beams through an optically non-linear medium (56), passing said at least two laser beams through a double refracting cystal (54) positioned in front of said optically non-linear medium (56), said double refracting crystal (54) having a length and being positioned relative to the optically non-linear medium (56) to introduce a spatial walk off and temporal offset into the said at least one of the two laser beams, said temporal offset and said spatial walk-off being opposite said temporal offset and said spatial walk-off introduced by said optically non-linear medium and being sufficient to cause said two pulsed laser beams to intersect temporally and spatially at a point within said optically non-linear medium (56).