(1) The illuminating mechanism that activates ions must have metastable state to form a three-level or four-level mechanism; and it is required that the metastable state has a long life, so that the number of particles is easy to accumulate and reverse. In order to make the laser glass have higher efficiency and low oscillation value, the four-level is superior to the three-level in terms of the energy level mechanism. When the energy interval between the final state and the ground state is greater than 1000 cm-1, the final energy level is almost empty at room temperature. Therefore, pumping at room temperature is also prone to particle number inversion.
At present, various activated ions of laser light have been generated in the glass, and the Nd3+ ion is optimal, which is a four-level mechanism, and the distance between the final state of the laser transition and the ground state energy level is about 1950 cm.
(2) Laser glass must have a variety of spectral properties. Including the absorption spectral properties, it is required to have a wide and many absorption bands in the radiant light of the excitation source, a high absorption coefficient, and the absorption band and the peak of the radiation band of the light source overlap as much as possible, which is beneficial to make full use of the excitation light source. Energy; fluorescence spectral properties, generally require that its fluorescence band is small and narrow, so that the output energy is not dispersed; at the same time, in order to convert the absorbed excitation light energy into laser energy as much as possible, the quantum efficiency of fluorescence is required to be as high as possible. The internal energy loss is as small as possible.
(3) The laser matrix glass must have good transparency, especially the absorption of the laser wavelength should be as low as possible. The high transparency of the matrix glass allows the energy of the optical pump to be sufficiently absorbed by the activated ions to be converted into a laser. The reduced transparency increases the absorption of the optical pump energy by the substrate and increases the temperature of the laser glass, which brings a series of disadvantages. At present, the radiation band of the optical pump is mostly located in the visible light and near ultraviolet and infrared regions, so it is necessary to select a material that is transparent in this region.
It is preferred to use an oxide and a fluoride glass in the inorganic glass. A compound containing a transition metal element such as iron, copper, lead, manganese, diamond, or nickel in the matrix glass. Strong absorption in the near-ultraviolet to infrared light causes a decrease in the transparency of the matrix glass. The main source of laser wavelength absorption in glass is impurities.
(4) Laser glass must have good optical uniformity. The optical non-uniformity of the laser glass causes the light wave to deform and generate a path difference after passing through the glass, which causes the oscillation threshold to improve the efficiency and the divergence angle to increase.
(5) Laser glass must have good thermal stability. During operation of the laser, the non-radiative transition loss of the activated ions and a portion of the optical energy of the ultraviolet and infrared absorption light pump of the matrix glass are converted into thermal energy that raises the temperature of the glass. At the same time, temperature gradients occur in the radial direction of the rod due to differences in endothermic and cooling conditions. In addition to causing a decrease in the optical uniformity of the laser glass to affect the laser performance, these factors may even cause the laser to be damaged by the poor thermo-mechanical properties of the glass.
(6) Laser glass must have good physical and chemical properties. In addition to the above requirements, in order to facilitate the manufacture, processing and use, laser glass is also required to have good physical properties. This includes a small tendency to devitrification and high chemical stability. Have a certain mechanical strength and good light stability and thermal conductivity. Glass having a high degree of devitrification tends to cause glass production, especially in the production process of bulk glass, and it is difficult to obtain a glass having high optical uniformity.
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