Method and device for sum-frequency generation of light pulses

摘要

This invention relates to the field of laser technology and more particularly concerns to the sum-frequency generation method, where laser pulses are combined by adding their optical frequencies in a second-order nonlinear medium (3). In order to increase energy of generated sum-frequency pulses or to generate shorter sum-frequency pulses than initial light pulses, the initial light pulses are directed to the input side of the second-order nonlinear medium (3) in pairs or one by one. A first light pulse (1) of a pair or light pulses (1,1') passes through the nonlinear medium (3) without taking part in a nonlinear interaction and then it is returned via a delay line comprising mirrors (5,5') to the input side of the same second-order nonlinear medium (3). There, the first light pulse (1) overlaps in space and time with a second light pulse (1')of the pair of light pulses. In the nonlinear medium (3) the non-collinear sum-frequency between the two light pulses (1,1') is generated. The delay line may comprise a half-wave plate for rotating the polarisation of the first light pulse by 90°, i.e. type II phase-matching may be used. Instead of a pair of light pulses a sequence of identical laser pulses may be used. In this case, by properly setting the delay time, a pulse shortening between the generated sum-frequency and the input laser light may be achieved. This scheme may be used for pulse compression of a laser pulse stretched in time in a CPA using fibre amplifiers.