Research On Two Micro-meters Holmium Single-doped Vanadates Host Solid-state Laser

The laser in the region of 2μm is not only in the atmospheric transparency window and safe to the eye of human, but also covering many atomic and molecular absorption peak. The laser is very important in many fields such as spectroscopy, remote sensing, laser communication, laser surgery, laser processing and environmental monitoring. However, there is different output performance of laser for different requirements. In order to meet the requirements of 2μm solid-state laser in different fields, the gain media with different characteristics should be adopted. At present, it is the single Ho doped solid laser that could meet this requirement at room temperature; however, the optional range of the gain medium is very small. Therefore, exploring new single Ho doped gain medium, it is very important for 2μm solid-state laser with scientific value. In account of this, this dissertation intends to make efforts on the research of the new single Ho doped vanadium oxide matrix solid laser, in order to make some contribution to the development of some fields.Firstly, several important 2μm solid-state lasers have been described and analyzed detailedly. It it necessry to obtain 2μm high performance laser with the gain medium of Ho-laser pumped by Tm-laser. Through the research of spectral properties, crystal in the distribution of temperature field and thermal lens effect, it points out the advantages of single Ho doped vanadium laser crystal in 2μm laser output performance and thermal management.Based on the energy transition theory and four-energy level laser medium, the rate equation model has been developed considering ground-state depletion and up-conversion loss. Under this model, we disscuss the influences of relative laser parameters, such as pump source, laser crystal and laser resonator, and obtain the pump beam waist position, the optimum pump laser, the oscillating light matching and transmission of output mirror optimum range.At last, it points out that the single Ho doped vanadate crystal is very excellent 2μm laser crystal.Secondly, using 1.94μm Tm-fiber laser as the pumping source, we study the theoretical analysis and experimental about the continuous wave output of single Ho vanadium doped laser. Based on the analysis of the thermal lens effect, the design and stability of the cavity are analyzed. The Ho:YVO₄ laser output of 12.3W was obtained under 34 W incident pump power with the slope efficiency of 44.5%. As for Ho:Gd VO₄, we obtained 11.2W laser output under 34.3W incident pump power with the slope efficiency 40.1%. In addition, the relationship of the maximum output power with the temperature of the heat sink is measured at room temperature, and it shows that the single Ho doped vanadium laser has lower temperature sensitivity.Furtherly, the characteristics of the laser output of the active-Q single doped Ho vanadium laser are analyzed and studied on the experiments. According to the principle of the Q-technology, the rate equation of the acoustic Q is established. The feasible method of improving the pulse energy, peak power and the width of the compression pulse is analyzed by usin g rate equation. At the repetition frequency of 10 k Hz, the Ho:YVO₄ laser output of 11.4W was obtained under 34.2W incident pump power with the slope efficiency of 41.2% at 2052 nm, corresponding to the minimum pulse width of 19.3ns. As for Ho:Gd VO₄, we obtained 2048 nm 10.2W laser output with the slope efficiency 37.3%, corresponding to the minimum pulse width of 5.8ns. The output laser of two vanadium crystal is close to the diffraction limit of the beam quality, and is the TEM00 mode laser output.Finally, the characteristics of the passively Q-swiched single Ho doped vanadate laser are analyzed and studied on the experiments. In theory, the research on the characteristics of Cr²⁺:Zn S crystal shows out that the Cr²⁺:Zn S crystal is suitable for 2μm passively Q-switched laser. The rate equation model has been developed for passive Q-switched laser. Using this model, we simulate Ho:YVO₄ laser crystal population inversion, saturated absorption of ground state particle number and resonant photon number under the time and space dynamic evolution process. At the cavity length of 120 mm, the Ho:YVO₄ laser output of 8.1W was obtained with the slope efficiency of 32.7% at 2053.2nm, corresponding to the minimum pulse width of 161.6ns and the maximum repetition frequency of 114.6k Hz. As for Ho:Gd VO₄, we obtained 2049.1nm 8.4W laser output with the slope efficiency of 31.1% at the cavity length of 110 mm, corresponding to the minimum pulse width of 43.2ns and the maximum repetition frequency of 111.2k Hz.