There is a possibility that an isomer can be found which could be used to obtain a sufficient population inversion density to bring about nuclear lasing. If it can be realized, a gamma ray laser ("graser") will be a new source of radiation in the $\sim$ 1A region of unexcelled spectral brightness and coherence, and can be expected to have revolutionary consequences for physics, biology, and chemistry. The result of our research is that the effects of crystallinity are of crucial importance in considerations regarding gamma-ray lasers, bringing in new elements to laser theory which could very well prove decisive in determining whether grasing can or cannot be achieved.
Certain multi-beam Borrmann eigenmodes of the radiation field in a perfect crystal have much stronger coupling to the emitting nuclei, and much less photoabsorption, than modes in the amorphous case. These modes may be selectively fed by nuclear transitions of the proper multipolarity. A crystal containing such emitters would require orders of magnitude less population inversion density in order to lase than would an amorphous sample of similar material.
Multi-beam Borrmann modes also have several applications to single-photon optics, particularly the problem of anomalous emission of a $\gamma$-ray by an internal source of multipolarity M1 or higher. While this effect can occur for a 2-beam Borrmann mode, even stronger anomalous emission is possible into multi-beam Borrmann modes. In addition, certain multi-beam Borrmann modes can anomalously transmit resonant radiation through a Mossbauer crystal. (This cannot occur for the 2-beam modes, except for the case of an E1 transition, since the Borrmann mode couples strongly to the nuclei and thus will be strongly absorbed at resonance.)