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Research On Properties Of 2-micron Ho:LuVO4 Solid-state Laser

Posted on:2017-03-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z CuiFull Text:PDF
GTID:1108330503969912Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
2 μm wave band falls into the spectrum of atmospheric window and locates in a region that is safe to human eye, also it covers the absorption peaks of many atoms and molecules. Therefore, 2 μm lasers have wide applications in the fields of laser medicine and laser ladar. What’s more, high peak power 2 μm pulse lasers are highly efficient pump sources for optical parametric oscillators and optical parametric amplifiers in mid-infrared 3-12μm region. With the rapid development in recent years, the implementation of 2 μm Tm3+-doped or Ho3+-doped solid-state lasers becomes increasingly mature. And various oxides and fluorids based Ho3+-doped solid-state laser operating at the room temperature have been extensively studied. Even so, in order to satisfy the demands from different fields, it is still of great significance from both research and application perspectives to seek new hosts for Ho3+ doped laser medium. Thus, in this paper, researches on novel Ho:Lu VO4 laser media and its 2 μm output characteristics have been carried out, hoping to make a contribution to the expansion of the related fields.First of all, we reviewed the evolution of 2 μm lasers and pointed out the importance of Ho3+-doped lasers in the development of the 2 μm lasers through analyzing the technical schemes for obtaining 2 μm laser output. By comparing the vanadate, oxide and fluorid hosts, the advantage of the 2 μm solid-state lasers with vanadate host was verified. Also, an elaboration on the development of the vanadate based 2 μm solid-state lasers is given.Then, the absorption spectrum, fluorescence spectrum and the fluorescent lifetime of the Ho:Lu VO4 crystal were accurately measured. Based on Judd- Ofelt theory and Füchtbauer- Ladenberg equation, we also calculated the spectral parameters and spectral emission cross section of the Ho:Lu VO4 crystal in 2 μm region. The possible oscillation wavelength and polarization state of the Ho:Lu VO 4 crystals were theoretically analyzed under different population inversion ratios. A thermal effect model of a single-ended pump Ho: Lu VO4 crystal was established as well. By numerical analysis, we obtained the interior temperature field as well as the thermal focal length of the Ho:Lu VO4 crystal, and layed a solid foundation for the design of the single end-pumped Ho:Lu VO4 lasers.Next, a quasi-four-level rate equation model was theoretically established to describe the Ho3+ doped laser system. On the basisi of the parameters of the Ho:Lu VO4 crystal, we numerically solved the rate equation model. Parameters such as up-conversion loss and round-trip loss that influence the output characteristics of Ho:Lu VO4 laser were discussed. By intergrating the thermal focal lens of the Ho:Lu VO4 crystal together, we further designed a resonant cavity for the single endpumped Ho:Lu VO4 laser, and discussed the influence of the cavity length and the curvature of output coupler on the distribution of the oscillating laser spots in the center of the crystal as well as the stability of the cavity. Experimentally, by deploying a Tm:YAP solid-state laser emitting at 1937.5 nm as the pump source, the influence of the transmission of the output coupler, the cavity length, and the working temperature on the output characteristics of Ho:Lu VO4 lasers was analyzed. By using a 20% transmission coupler and a 110 mm cavity, we obtained a maximum continuous wave output power of 4.1 W at 2058.4 nm with the crystal operating at 290 K. The absorbed pump power was measured to be 12.3 W, which corresponds to a slope efficiency of 43%.Furthermore, a rate equation model of the Ho3+-doped Q-switched was established theoretically. On the strength of the parameters of the Ho:Lu VO4 crystal, both actively and passively Q-switched rate equation models were solved numerically, and the influence of the pulse width, the pulse energy, and the peak power were discussed. Next, a Tm:YAP solid-state laser emitting at 1937.5 nm was employed as the pump source in the experiment. For the actively Q-switched operation, we compared the influence of the transmission of the output coupler and that of the repetition frequency on the output characteristics of an acoustic-optic Q-switch based actively Q-switched Ho:Lu VO4 laser. When the transmissivity was 20%, the repetition frequency was 20 k Hz, and the absorbed pump power was 12.3 W, the maximum average output power of 4.1 W in the stable Q-switched operation was obtained with a minimum pulse width of 29.3 ns, the slope efficiency was calculated to be 42.1%. For the passively Q-switched operation, by employing a Cr2+:Zn S crystal that has a initial transmission of 86.3% as the saturate absorber, we meticulously analyzed the influence of the transmission of the output coupler on the output characteristics of the passively Q-switched laser. The maximum average output power of 2.3 W in the stable passively Q-switched operation was obtained at the wavelength of 2057.8 nm under a transmissivity of 50% and an absorbed pump power of 12.3 W, resulting in a slope efficiency of 42.1%. The minimum pulse width and the maximum repetition frequency were measured to be 100 ns and 34.2 k Hz, respectively. In addition, we also analyzed the beam qualities of both actively and passively Q-switched lasers, they were close to diffraction limit, in other words the output modes could be treated as fundamental TEM00.At last, theoretical analysis on the actively mode-locked laser with amplitude modulation was conducted, we discussed the influence of the etalon effect on the pulse width of the mode-locked laser pulse, and the output power of the lasers in both mode-locked and continuous wave operations. Based on the analysis of the relaxation oscillation, we compared the stability of output power of the Tm:YAP solid-state laser and that of the Tm3+-doped fiber laser, and found that Tm3+-doped fiber laser is more suitable in terms of being the pump source. On the basis of the theory of the Newtonian telescope, a resonant cavity for the mode-locked laser was designed, and the influence of the distance as well the angles between the mirrors on the distribution of the laser spot in the cavity and the stability of the cavity was analyzed. Experimentally, with a Tm3+-doped fiber laser emitting at 1940.3 nm being utilized to pump the Ho:Lu VO4 crystal, we accomplished the actively mode-locked output with an acoustic-optic modulator. When 16.3 W pump power was absorbed, a maximum average output power of 3.04 W at 2073.8 nm was achieved in the stable mode-locked operation with a slope efficiency of 22.9%, corresponding repetition frequency and the minimum pulse width were 82.7 MHz and 363.3 ps. The beam quality factor M2 of the mode-locked laser was characterized to be 1.4.
Keywords/Search Tags:2 μm laser, Ho:Lu VO4 crystal, Q-switched laser, actively mode-locked laser
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