The mother crystals developed so far and laser wavelengths by light emission centers are summarized in the following table. Also, the examples of developments are introduced in the subsequent sections 5-5 and 5-6.

It is necessary to make a little more detailed study of the relationship between excitation and laser transition, taking the Nd: YAG as an example. The strong absorption band around 810nm observed in Fig. 6 corresponds to the transition of the Nd from its base state of ⁴I9/2 to ⁴F5/2. When a laser diode is used, it is tuned to this strong absorption band. The transition from the ⁴F5/2 to the laser emission level of ⁴F3/2 occurs without radiation. The Nd: YAG, as shown in Fig. 6, emits more than 20 rays. In most of them, laser emissions are observed. The main transition among them is from ⁴F3/2 to ⁴I11/2, providing 1.06µm emissions. In addition, 1.32µm emissions by the transition from ⁴F3/2 to ⁴I11/2, and 0.946µm emissions by the transition from ⁴F3/2 to ⁴I9/2 are also included.