TLDR: A gamma-ray laser, also known as a graser, is a hypothetical device that could produce coherent gamma rays. It has potential applications in medical imaging, spacecraft propulsion, and cancer treatment. The development of a practical gamma-ray laser involves interdisciplinary research in fields such as quantum mechanics, nuclear and optical spectroscopy, chemistry, solid-state physics, and metallurgy.
A gamma-ray laser is similar to a regular laser, but instead of producing coherent visible light, it would produce coherent gamma rays. Gamma rays are a type of electromagnetic radiation with very high energy and short wavelengths. They can penetrate through materials and are used in various scientific and medical applications.
The challenge in creating a gamma-ray laser lies in obtaining a sufficient concentration of resonant excited nuclear states for collective stimulated emission to occur. This involves dealing with the broadening of the gamma-ray spectral line, which can be caused by factors such as the lifetime of the excited state and inhomogeneous broadening.
Researchers have explored different approaches to overcome these challenges. One approach involves using recoilless radiation, known as the Mössbauer effect, which exhibits a sharp line on top of the Doppler-broadened background. Another approach is to use two-stage neutron-gamma pumping, where neutron capture occurs in a parent-doped converter, generating Mössbauer radiation that is then absorbed by ground-state nuclei in the graser.
There are also efforts to use collective electron oscillations to drive nuclear transitions and enable gamma-ray laser operation. This approach involves a triad of isomeric states, including a long-lived storage state, an upper lasing state, and a lower lasing state. The intense optical laser is used to slosh the electron cloud back and forth, saturating the forbidden transition and stimulating the emission of resonant gamma radiation.
The development of a practical gamma-ray laser requires expertise in various scientific and engineering fields. While it is still a hypothetical device, the research in this area continues to explore the possibilities and potential applications of gamma-ray lasers.