Diffraction on helical acoustic-surface-wave delay lines and the concept of an anisotropic edge lens

It is shown experimentally that the straight edge between two intersecting planes on Bi12 GeO20 acts, in accordance with the diffraction scaling theorem, as an acoustic-surface-wave lens. A helical delay line can be treated as a repetitive stack of edge lenses. Under certain conditions, the `beam waveguide¿ may be metastable.