HIGH-ORDER HARMONIC-GENERATION IN COLLIDI NG BEAMS

A method for the generation of high-order harmonics in two interfering waves is proposed. It is shown that phase matching is possible in suc h a method and its consequence is a considerable increase in the effic iency of conversion of radiation to a harmonic with a given number. Th e increase is particularly large when harmonics are generated in a low -density (subcritical) plasma, The conditions are found under which th e increase is about four orders of magnitude. The use of two interferi ng beams makes it possible to separate angularly the generated harmoni cs without recourse to spectroscopic devices.