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Provides a definitive overview of the current status of gamma-ray lasers including contributions from scientists pursuing active research in areas relevant to the graser problem. Describes a range of programmes which deal with selecting candidate nuclei, procuring the right lasing medium and forming it into an acicular geometry, working in an energy regime that enables utilizing the Mossbauer Effect, using the Campbell-Borrmann Effect to decrease electronic absorption, designing basic experiments that demonstrate critical steps necessary to produce a graser, and clarifying a number of theoretical problems specific to the nuclear laser.
This report is addressed to the problem of the state-of-the-art of gamma ray laser development. It is intended to identify the various disciplines and specific research areas which can best contribute to resolving the question of 'graser' feasibility. Topics discussed include the following: The basic mechanisms of laser action; Gamma ray emission from nuclear isomers; The resonance cross section; Nonresonant absorption; Photon kinetics; Inhomogeneous line breadths; Problems of pumping.
Recent approaches to the problem of the gamma-ray laser have focused upon upconversion techniques in which metastable nuclei are pumped with long wavelength radiation. At the nuclear level the storage of energy can approach tera-Joules per liter for thousands of years. However, any plan to use such a resource for a gamma-ray laser poses problems of a broad interdisciplinary nature requiring the fusion of concepts taken from relatively unrelated field of physics. Our research group has described several means through which this energy might be coupled to the radiation fields with cross sections for stimulated emission that could reach 10 to the minus 17th power sq. cm. Such a stimulated release could lead to output powers as great as 3 X 10 to the 21st power Watts/liter. Since 1978 we have pursued an approach for the upconversion of longer wavelength radiation incident upon isomeric nuclear populations that can avoid many of the difficulties encountered with traditional concepts of single photon pumping. Recent experiments have confirmed the general theory and have indicated that a gamma-ray laser is feasible if the right combination of energy levels and branching ratios exists in some real material. Of the 1,886 distinguishable nuclear materials, the present state-of-the-art has been adequate to identify 29 first-class candidates, but further evaluation cannot proceed without remeasurements of nuclear properties with higher precision.
The possibility of extending the laser principle into the hard x-ray region above a few keV depends upon the ability of a pump to create the critical density of population inversion for which gain overcomes loss by absorption. Although this critical density decreases with the wavelength of the radiation to be stimulated, the power required to generate it depends upon the lifetime of the state being pumped. The lifetimes of inner-shell vacancies of atoms are very short. Nuclear states, on the other hand, have much longer lifetimes, ranging from fractions of picoseconds to millennia. Moreover, in the so-called recoilless or Moessbauer transitions of nuclear isomers, it was observed that the resonance cross section often exceeds the nonresonant absorption cross section by several orders of magnitude: just the condition for lasing in an inverted population. If, other things being equal, the absorber foil of a Moessbauer experiment contained an excess of excited states, then, instead of the absorption dip normally observed at resonance, there would be an increase of intensity, and amplification by stimulated emission would be achieved. The problem in making a gamma-ray laser is, therefore, simply that of obtaining an inverted population without inhibiting the Moessbauer effect. Research on this problem is reviewed.
The most productive approaches to the problem of the gamma ray laser have focused upon upconversion techniques in which metastable nuclei are pumped with long wavelength radiation. At the nuclear level the storage of energy can approach tera-Joules (10(exp 12)J) per liter for thousands of years. However, any plan to use such a resource for a gamma ray laser poses problems of a broad interdisciplinary nature requiring the fusion of concepts taken from relatively unrelated fields of physics. Our research group has described several means through which this energy might be coupled to radiation field with cross sections for stimulated emission that could reach 10(exp -17) sq cm. Such a stimulated release could lead to output powers as great as 3 x 102 Watts/liter. Since 1978 we have pursued an approach for the upconversion of longer wavelength radiation incident upon isomeric nuclear populations that can avoid many of the difficulties encountered with traditional concepts 0 single-photon pumping. Experiments have confirmed the general theory and have indicated that a gamma-ray laser is feasible if the right combination of energy levels and branching ratios exists in some real material. Of the 1,886 distinguishable nuclear materials, the present state-of-the-art has been adequate to identify 29 first-class candidates, but further evaluation cannot proceed without remeasurements of nuclear. A laser-grade database of nuclear properties does not yet exist but the techniques for constructing one have been developed and utilize under this contract.
Recent approaches to the problem of the gamma-ray laser have focused upon upconversion techniques in which metastable nuclei are pumped with long wavelength radiation. At the nuclear level the storage of energy can approach tera-Joules (10 to the 12th power J) per liter for thousands of years. However, any plan to use such a resource for a gamma-ray laser poses problems of a broad interdisciplinary nature requiring the fusion of concepts taken from relatively unrelated fields of physics. Since 1978 we have pursued an approach for the upconversion of longer wavelength radiation incident upon isomeric nuclear populations that can avoid many of the difficulties encountered with traditional concepts of single photon pumping. Recent experiments have confirmed the general feasibility and have indicated that a gamma-ray laser is feasible if the right combination of energy levels and branching ratios exists in some real material. Resolution of the question of the feasibility of a gamma-ray laser now rests upon the determination of: 1) the identity of the best candidate, 2) the threshold level of laser output, and 3) the upconversion driver for that material.
The most productive approaches to the problem of the gamma-ray laser have focused upon upconversion techniques in which metastable nuclei are pumped with long wavelength radiation. At the nuclear level the storage of energy can approach tera-Joules (10(exp 12)J) per liter for thousands of years. However, any plan to use such a resource for a gamma-ray laser poses problems of a broad interdisciplinary nature requiring the fusion of concepts taken from relatively unrelated fields of physics. Our research group has described several means through which this energy might be coupled to radiation fields with cross sections for stimulated emission that could reach 10(exp -17)sq cm. Such a stimulated release could lead to output powers as great as 3 x 1021 Watts/liter. Since 1978 we have pursued an approach for the upconversion of longer wavelength radiation incident upon isomeric nuclear populations that can avoid many of the difficulties encountered with traditional concepts of single photon pumping. Experiments have confirmed the general theory and have indicated that a gamma- ray laser is feasible if the right combination of energy levels and branching ratios exists in some real material. Of the 1,886 distinguishable nuclear materials, the present state-of-the-art has been adequate to identify 29 first- class candidates, but further evaluation cannot proceed without remeasurements of nuclear properties with higher precision. Gamma-ray laser, Ultrashort wavelength laser.
The concept of the graser (or gamma-ray laser) is discussed, and recent Russian and American proposals are surveyed. The difficulties in building a gamma-ray laser are outlined; and specific recommendations are made for delimiting the extent of NRL involvement in graser research in the near future.
Laser sources generating sub-nm radiation, using recoilless nuclear transitions in solids, have been proposed for years. This review examines, from the standpoint of kinetics, many solutions (viz., narrowed line, explosive neutron pump, two-stage pump, two-step pump) that have been proposed for the basic problem: that pumping can inhibit or destroy the Moessbauer and Borrmann effects, which are essential for gain. 4 refs.
The development of a gamma-ray laser has stood as a formidable challenge to science and scientists for more than thirty years. In that time visible lasers have become commonplace in everyday life, appearing in science, surgery, supermarket and, through the compact disc, sound. No less remarkable has been the march toward ever increasing photon energies, now reaching soft X-rays. Still, the ultimate goal of the coherent production of gamma-rays remains unfulfilled, despite the recognition of its promise so early after the invention of the ruby laser. The strongly interdisciplinary nature of the problem requires a fusion of concepts from traditionally unrelated fields like quantum electronics and nuclear physics and this has provided both the challenge and the attraction. From this intriguing combination it is understandable that for many the gamma-ray laser has become more than just a topic of research, but instead of life-long goal.