Rami Arieli: "The
Laser Adventure" Section 6.5.2 page 1
6.5.2 X-Ray Laser
Theoretically, since the physical
nature of electromagnetic waves is the same with no dependence on their
wavelength, it is logic to think that it is possible to create laser at
any wavelength.
In practice, there is a problem
creating a laser that operate in the short wavelength of x-Rays and g-Rays.
Explanation:
The lasing process depend on the properties of the medium in which
lasing occurs.
The requirements from the active medium depend on the wavelengths which
needed to be created:
-
In the visible spectrum, and in the Near Infra-Red (NIR) spectrum, the
radiation is emitted as a result of electronic
transitions between outer electrons energy levels of the atoms or molecules.
-
To create radiation (photons) in the X-Rays spectrum a much higher energy
is needed. Such energy can come from transitions
from the outer energy levels into inner energy levels. Exciting
these energy levels require much more energy for pumping, and the lifetime
of the excited states is very short (of the order of pico-seconds).
Conclusion: To
create a laser in the X-Rays spectrum region,
requires a large amount of pump energy, in a very short time.