Inversionless gain at gamma-ray transition via nuclear coherence created by optical driving

A possibility of amplification without population inversion at gamma-ray transition due to excitation of nuclear coherence via coherent optical driving of electron coupled with nucleus is demonstrated. It is shown that hyperfine splitting and isomeric shift provide the principal means for excitation of nuclear coherence by optical field and realization of amplification without inversion in gamma-ray range. It does not mean that it is the only way to achieve the inversionless amplification in nuclear transitions. It does not also mean that this approach is free of any problems. We have neglected a number of facts to obtain the results reported. In particular, it is necessary to take into account the effects of inhomogeneous broadening and nonresonant losses. This will be our objects of the future investigations. (authors)