1) There must be a metastable state in the luminescence mechanism that activates the ions, forming a three-level or four-level mechanism; and requiring a longer life for the metastable state, so that the number of particles is easy to accumulate to achieve inversion. In order to make the laser glass have higher efficiency and lower oscillation value, the four-level energy level is superior to the three-level energy level. When the energy interval between the final state energy level and the ground state energy level is greater than 1000 cm −1 , the final state energy level is almost empty at room temperature. Therefore, pumping at room temperature is also prone to inversion of the population number. The various active ions that have generated laser light in the glass, with the best Nd3+ ion, are four-level mechanisms, and the distance between the final state of the laser transition and the ground state energy level is approximately 1950 centimeters.
(2) The laser glass must have various suitable spectral properties. Including the absorption spectrum properties, it is required that the radiation light of the excitation light source has a wider and more absorption band, a high absorption coefficient, and the absorption spectrum band overlaps with the peak of the radiation band of the light source as much as possible, which is favorable for fully utilizing the excitation light source. Energy; fluorescent spectral properties, generally require its fluorescence spectrum is small and narrow, so that the output energy does not disperse; At the same time in order to make the absorbed excitation light energy as much as possible into the laser energy, but also requires the quantum efficiency of fluorescence 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 enables the energy of the optical pump to be fully absorbed by the activating ions and converted into a laser. The decrease in transparency increases the absorption of light energy by the substrate, and the temperature of the laser glass rises, which brings a series of disadvantages. Most of the radiation band of the optical pump is in the visible light and near ultraviolet and infrared regions, so it is necessary to choose a material that is transparent in this region. Among inorganic glasses, oxides and fluoride glasses are suitable. If the matrix glass contains compounds of transition metal elements such as iron, copper, lead, manganese, diamond, nickel, etc., there is a strong absorption in the near ultraviolet to infrared, which will make the transparency of the matrix glass lower. The major 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 pass through the glass after the wave surface deforms and produces a process difference, which promotes the lowering of the oscillation threshold efficiency and the increase of the divergence angle.
(5) The laser glass must have good thermo-optic stabilization. When the laser is operating, the non-radiative transition loss of the active ion and the part of the light energy of the ultraviolet, infrared absorption light pump of the matrix glass are converted into heat energy that increases the temperature of the glass. At the same time, temperature gradients occur in the radial direction of the rod due to differences in heat absorption and cooling conditions. In addition to the fact that these factors reduce the optical homogeneity of the laser glass and affect the laser performance, even the laser glass is damaged due to poor thermo-mechanical properties.
(6) Laser glass must have good physical and chemical properties. In addition to the above requirements, laser glass is also required to have good chemical properties in order to facilitate manufacturing, processing, and use. This includes low tendency to devitrify and high chemical stability. Has a certain degree of mechanical strength and good light stability and thermal conductivity. A glass with a high devitrification tendency causes glass production, especially a production process of a large glass, and it is difficult to obtain a glass with high optical uniformity.