Interpretation of the Amazing Laser Technology : Laser Crystal

Laser crystal can transfer power from the outside world into crystal material with high parallelism and monochromatic laser in space and time through optical resonator. It’s the operation material of crystal laser. Laser crystal consists of luminescence center and host crystal. Most luminescence center of laser crystal is made up of active ion. While active ion partly replaces the positive ion of the host crystal to form doped laser crystal; while active ion becomes part of the host crystal, then it will become self-activated laser crystal.



Active ions used in laser crystal are mainly transition metal ions and trivalent rare-earth ions. The optical electron of transition metal ion is the 3d electron of the outer shell; this optical electron can be directly affected by the surrounding crystal field, its spectral characteristic differs in different structure type crystals. The 4f electron of the trivalent rare-earth ion is shielded by 5s and 5p electrons of the outer shell, thus reduces the effect of its surrounding crystal field; while the perturbation of the crystal field may lead to transition of the originally forbidden 4f electron, and forms narrow bandwidth absorption and fluorescence spectrums. So the change of the trivalent rare-earth ions in different crystals is obviously different from transition metal ions.

Host crystals used in laser crystal are mainly oxides and fluorides. As a host crystal, it should have stable physical and chemical characteristics; it can easily generate large size crystal with good optical homogeneity and low price. At the same time, we should notice the adaptability between the host crystal and the active ions: for example, the radius, electro negativity and valence state between host positive ion and active ion should be close as possible. Besides, we should also take into account of the impact of host crystal field upon active ion spectrum. For some host crystal with special function, it can directly generate laser with certain special function after mixed with active ions; for example, in some nonlinear crystals, after generating laser, active ion can be directly transferred into harmonic wave output through host crystal.