Transformation of waves in beams of variable cross section

An investigation is made of the feasibility of improving the characteristics of a stimulated scattering amplifier and of a hypersonic phase-conjugating mirror by the use of beams with variable cross sections. It is shown that in the process of amplification due to stimulated scattering of an external signal there is an infinite set of geometric profiles of pump beams with the same equivalent areas and with the same efficiency of conversion of the pump into the amplified radiation. In a hypersonic phase-conjugating mirror where four-wave mixing with a strong signal wave occurs over the whole length of the signal beam in a mixer it is possible to increase the reflection coefficient of the signal by adopting a signal beam geometry in which the cross-sectional area increases in the direction of motion of the signal.