What are the main bases of nonlinear optical materials?
Published Time:
2025-05-15
Source:
Laser crystals can convert the energy provided by the outside world into a crystal material with highly parallel and monochromatic lasers that are coherent in space and time through an optical resonant cavity. It is the working material of crystal lasers. Laser crystals are composed of two parts: the luminescent center and the matrix crystal. The luminescent center of most laser crystals is composed of activated ions, which partially replace the cations in the matrix crystal to form a doped laser crystal. When the activated ions become part of the matrix crystal component, a self-activated laser crystal is formed.
The activated ions used in laser crystals are mainly transition metal ions and trivalent rare earth ions. The optical electrons of transition metal ions are 3d electrons in the outer layer. In the crystal, this optical electron is susceptible to the direct effect of the surrounding crystal field, so its spectral characteristics are very different in crystals of different structural types. The 4f electrons of trivalent rare earth ions are shielded by the 5s and 5p outer electrons, which weakens the effect of the crystal field on them, but the perturbation of the crystal field makes the originally forbidden 4f electron transition possible, producing narrow-band absorption and fluorescence spectra. Therefore, the spectrum of trivalent rare earth ions in different crystals does not change as much as that of transition metal ions.
The matrix crystals used in laser crystals are mainly oxides and fluorides. As matrix crystals, in addition to the requirement of stable physical and chemical properties, easy growth of large-sized crystals with good optical uniformity, and low price, the compatibility between them and the activation ions should be considered, such as the radius, electronegativity and valence of the matrix cation and the activation ion should be as close as possible. In addition, the influence of the matrix crystal field on the spectrum of the activation ion should also be considered. For some matrix crystals with specific functions, lasers with certain characteristics can be directly generated after the activation ions are doped. For example, in some nonlinear crystals, the activation ions can be directly converted into harmonic output through the matrix crystal after generating lasers.
The activation ions used in laser crystals are mainly transition metal ions and trivalent rare earth ions. The optical electrons of transition metal ions are 3d electrons in the outer layer. In the crystal, this optical electron is easily affected by the direct effect of the surrounding crystal field, so the spectral characteristics of crystals of different structural types are very different. The 4f electrons of trivalent rare earth ions are shielded by the 5s and 5p outer electrons, which weakens the effect of the crystal field on them. However, the perturbation of the crystal field makes the originally forbidden 4f electron transition possible, producing narrow-band absorption and fluorescence spectra. Therefore, the spectra of trivalent rare earth ions in different crystals do not change as much as transition metal ions.
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