Gamma laser may deal with nuclear gain media. At first, we should verify the extent of the stimulated emission to the much shorter spectral range where the photon acts as a particle. The interactions of Gamma photons with atoms include three main mechanisms i.e, compton scattering, photoelectric and pair-production. Those events may be against the stimulated emission to create the coherent beams. On the other hand, the design of the resonator (reflectors) for gamma photons will be a major challenge. The fabrication of suitable mirrors is based on multilayer film coating using the stack of high z materials in pm thickness. Is it feasible?

A gamma ray source, that in principle could be turn into a gamma ray laser, may be conceived extending the principle at the basis of the wavelength tuning in a free electron laser. In a free electron laser, radiation is emitted by an oscillating dipole which is observed in the laboratory frame as Doppler shifted. This allows to tune the emission wavelength to the desired value. A Lorentz boost could be similarly considered for systems emitting light via other emission processes, as e.g. an atomic recombination. The necessity to achieve a large boost factor (ratio between relativistic mass and rest mass) which is the quantity determining the energy shift of the emitted photons, restricts the emitters to “light” systems. A process providing energetic photons that could then be Lorentz boosted to higher energies, could be annihilation of positronium, see e.g. the reference:

http://accelconf.web.cern.ch/AccelConf/FEL2010/papers/thpb11.pdf,

which may be found in full text on research gate too.

Dear Giannessi

Thank you for your comment. Electron-positron annihilation is a source of 510 keV gamma photons( photon pairs in opposite directions} usually used in PET tomography.

However, it is not a coherent source because it is not a gain medium to generate further coherent photons based on stimulated emission.

It can be a coherent source. Gain depends on the existence of a population inversion, and the population inversion is given by the existence of pairs of electrons and positrons available for annihilation. It is a matter of probability that stimulated emission, which proportional to the density of positronium available, takes over the spontaneous annihilation. The photon energy is 510keV when the process is observed in the rest frame. As explained in the reference, the emitted photons may be Doppler shifted. With a proper setup the gamma ray energy can be substantially larger, and the emission would be concentrated in a small solid angle.

Thank you for your comment, I am not sure that we can create inverted population without pumping? Is it similar to FEL scheme? The electrons and positrons may be accelerated thorough a wiggler in opposite direction and may annihilate simultaneously to generate gamma photons in opposite directions too. However, there is no reason that electron and positron kinetic energies can be efficiently converted to gamma photons. This is the gain that I believe is negligible. However, you may give us your advice. What is the pumping scheme? What resonator do you propose?

Inverted population is a consequence of the existence of Positronium. "Pumping" consists in the generation of positrons and in accelerating electrons and positrons to the desired energy. And I don't think a gamma ray mirror may be realized. This device should work without a resonator, similarly to single pass X-ray FELs amplifying spontaneous emission.

Is there any experimental achievement?

Technically, gain is correlated to inverted population and stimulated emission cross-section.The latter is proportional to laser wavelength square and spontaneous emission Einstein coefficient A.Therefore for gamma laser the lambda is in the order of pm and 10^6 times shorter than traditional lasers. This decreases the gain drastically, however if you forget coherence the amplified spontaneous emission (ASE) may be feasible, then the shortcoming is how to fabricate the periodic magnet in nanoscale ?!

What about X - ray and gamma laser lidars?

What applications do you predict?

To my knowledge, the fabrication of the reflectors at short wavelengeths ( x and gamma), implementing the suitable resonators enhance the beam quality of such lasers. The success to make such reflectors is developing a new brach of Optics: Nuclear Optics.

I proposed a way for generating \gamma-ray laser  (see arXiv.1408.3112 on the net lanl). I hope you or your freinds may realize it experimentally.

What about a nano wiggler?