We have previously shown that two-beam Borrmann modes of good single Mössbauer crystals offer the possibility of achieving nuclear lasing at population-inversion densities substantially lower than would be required in an amorphous sample of the same material [J. T. Hutton, J. P. Hannon, and G. T. Trammell, Phys. Rev. A 37, 4269 (1988)]. In this paper we discuss the further improvements which are obtained in multibeam Borrmann modes (which consist of the coherent superposition of three or more plane waves within the crystal). These modes can have smaller absorption coefficients, and more importantly, stronger coupling to the nuclei, as well as sharper collimation than do corresponding two-beam modes, leading to even lower requirements for the population-inversion density needed to induce lasing.

• Received 19 October 1987

DOI:https://doi.org/10.1103/PhysRevA.37.4280