This section outlines the basic historical developments related to solid state laser materials and technology. It shows briefly how advances in basic science related to rare-earth-ion spectroscopy progressed, together with an understanding of physical processes in solids and solid state materials, which led to the first operation of the laser and subsequently to many technological advances.
In 1907, Becquerel made early observations of a rare earth's luminescence at low temperatures. During the years 1930-1940, an extensive theoretical analysis of the spectra of rare-earth ions was conducted, led by scientists such as Bethe, Kramers, Van Vleck, Racach, and others.
From 1961 through 1968, Dieke and others conducted research that led to the full assignment of the energy levels of trivalent rare-earth trichlorides. This whole assignment was accompanied by theoretical calculations of the transition strengths (mainly the electric dipole but also the magnetic dipole transitions) among various electronic levels in rare-earth ions.
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