The most progress in searching for active media for NPLs, studying their charac­teristics, and developing various nuclear-laser devices was achieved when high — pressure gas media were used. However, there have been repeated attempts in Russia and the United States to pump different condensed media with nuclear radiation and carry out feasibility studies on developing powerful nuclear-laser devices based on these media. The active material in solid-state and liquid lasers is a dielectric in a condensed phase. As compared to gases, it is possible to create a higher density of active particles in condensed media, and, as consequence, to obtain more specific output energy of laser radiation.

When uranium, for example, is introduced into a condensed media it is possible to achieve essentially uniform excitation of the active volume at close to 100 % deposition efficiency (due to a small path length for charged nuclear particles in a condensed medium). Therefore in the initial stage of NPL investigations at the end of the 1960s and the beginning of the 1970s, when known gas lasers operated only at low pressures, the emphasis was on condensed media. At that time, these studies were carried out at VNIIEF [1—3] in Russia and in the laboratories of the North American Rockwell Corporation, General Atomics, etc. in the United States (see the literature cited in publications [4—6]). Later, other laboratories became involved in the investigation of condensed-media NPLs. A significant number of studies were fulfilled at FEI [Physics and Power Engineering Institute] (Russia) and the University of Missouri-Columbia (USA).

Two pumping alternatives were considered for excitation of condensed-media NPLs: immediate (direct) pumping using nuclear radiation when nuclear reactions occur inside the laser medium; and pumping with help of optical radiation from intermediate devices—nuclear-optical transformers or convertors (nuclear-excited plasma and solid-state or liquid scintillation media). In the first case, the pumping region and the region where population inversion is created coincide, in the second, they are spatially separated.

© Springer Science+Business Media New York 2015 S. P. Melnikov et al., Lasers with Nuclear Pumping, DOI 10.1007/978-3-319-08882-2_11