Abstract
The results are given of a theoretical and experimental investigation of three-photon parametric amplification and generation of ultrashort light pulses in KDP and α-HIO3 crystals. It is shown that parametric amplifiers can be used in spectroscopy to determine the shape and duration of ultrashort weak optical signals. Commissioning of a continuously tunable optical parametric oscillator with a high pulse repetition frequency (up to 25 Hz) is reported.