RECENT PROPOSALS FOR GAMMA-RAY LASERS

Proposals for grasers based on recoilless gamma-ray emission in solid hosts must consider the availability and compatibility of essential co mponents, kinetic behavior (with particular regard to the uncertainty principle), and side effects of the pump at the requisite intensity. W e categorize and discuss several recent proposals for linewidth contro l and for creating population inversion (including lower state decay, interlevel transfer with coherent radiation, and incoherent megaelectr onvolt-range bremsstrahlung). We show that several are fallacious, tha t the prospects for two-step pumping from a separated isomer are uncer tain, and that the best hope for a successful system may be inversionl ess lasing.