Distortions of time characteristics in parametric up-conversion of ultrashort laser pulses

The dependence of the sum-frequency field on the fields of different frequencies mixed in a nonlinear medium is obtained for signals of 10^–10–10^–12 sec duration. The conditions are formulated for the smallness of distortions of the time characteristics of the investigated pulses and methods are proposed for restoring these characteristics in parametric frequency up-conversion.