| Stimulated Raman scattering is one of the important frequency conversion methods, belonging to the third-order nonlinear optics. The scattering spectra range from UV to Near-infrared, which have the potential applications in information science, laser measurement, laser medicine and national defense. Due to the small size, high Raman gain coefficient and good thermal and mechanical properties of the crystal materials, all solid-state Raman laser has become one of the most avtive fields in the Raman laser research. Among the Raman crystal materials, BaWO4, KGW, Nd:YVO4, and Nd:GdVO4et al are most used to generate Raman laser. However, each kind of Raman crystals are with certain limitation in Raman application and the scattering wavelength is dependent on the lattice vibration mode. The steps for exploring novel and practical Raman crystal material are never stop. These Raman crystals have the advantage porperties in terms of abundant Raman vibration mode, high Raman gain coefficient, good thermal an mechanical properties, high laser damage threshold, and good crystal grow habit.This paper have theoretically and experimentally studied the performace of the stimulated Raman scattering lasers based on a novel Raman material, α-BaTeMo2O9crystal. The α-BaTeMoaO9crystal was grown by the State key lab. Of crystal materials, Shandong University, which possesses lager size, wide transmission bands, abundant Raman vibration mode, moderate Raman gain coefficient and thermal conductivity, and high laser damage threshold. Firstly, we have classified the all lattice vibrational mode and calculate the Raman scattering coefficiency with the different Raman configurations. The relationships between Raman vibration peak and atom vibration group were given. In addition, by using the method of spontaneous Raman spectra comparision, the steady-state Raman gain coefficient of a-BaTeMo2O9crystal with Z(XX)Z Raman configuration was calculated. Based on the analysis of the Raman spectra, the generations of the α-BaTeMo2O9Raman laser have been systematic investigated. The high efficiency first-order, second-order, and third-order Stokes Raman laser have been obtained based on the α-BaTeMo2O9crystal, respectively. What is more, a second-order and third-order simulataneous dual-wavelength Raman laser generation was also achieved. The main content of this dissertation includes:1. The structure of lattice and optical and thermal properties for α-BaTeMo2O9crystal have been simply introduced. Based on the crystal structure, all of the vibration mode was calculated and classified as follows:Г=78A1+78A2+78B1+78B2, and group theory predicts that all of the vibration mode belong to Raman activel mode. The Raman scattering coefficient was calculated and the relationships between Raman vibration peak and atom vibration group were given, in which the～900cm-1Raman shifing was generated by antisymmetric stretching modes of the Mo-O-Mo bridge. The X-, Y-and Z-cut polarized spontaneous Raman spectra were measuremented, and the experimental results were consistent with the theoretical analysis.(Chapter2)2. The methods for the calculation of Raman gain coefficient were systemically introducted. The Raman gain coefficient of the α-BaTeMo2O9crystal with Z(XX)Z configuration was calculated to be2.4cm/GW@1.06μm by the method of spontaneous Raman spectra comparision. The rate equations have been established to guide the experiments for intracavity and extracavity Raman lasers. The first-order Stokes Raman laser based on the bulk α-BaTeMo2O9crystal was firstly studied:By using a lamp-pumped Q-switched Nd:YAG laser as a Raman pump source, a maximum1.178μm first-order Stokes pulse energy of15.1mJ was achieved with a optical-to-optical conversion efficiency of31.5%; A maximum pulse energy of1.07mJ Raman laser was obtained driven by a pulsed laser diode pumped Nd:YAG/Cr4+:YAG laser with repetition rate of670Hz. This kind of lasers have a potential application in laser ranging. With a diode-side-pumped Nd:YLF Q-switched laser intracavity pumping, a maximum1.164μm Raman output power was2.7W, corresponding to the maximum single pulse energy and peak power of1.08mJ and67.5kW, respectively.(Chapter3)3. Based on experimental research on the first-order Stokes Raman laser, a second-order Raman laser was achieved with optimum resonator design, driven by a diode-side-pumped Nd:YLF laser. The maximum output power, single pulse energy and peak power were1.37W,0.55mJ and137kW, respectively. We firstly demonstrated a dual-wavelength α-BaTeMo2O9Raman laser with the second and third-order Stokes wavelength simultaneous output. A total maximum output pulse energy of13.6mJ was achieved, giving a optical-to-optical conversion efficiency and a slope efficiency of35.9%and54.5%, respectively, which contains20.1mJ second-order Stokes pulse energy and7.2mJ third-order Stokes pulse energy. What is more, the relationship between second-order and third-order Stokes output energy and output coupler was analysed in details.(Chapter4)4. The thermal effect for laser crystal and Raman gain medium have been systematic studied, and the thermal focusing length were given through theoretical derivation. With optimum optical resonator design, a high pulse energy eye-safe Raman laser was achieved, with1.5μm output pulse energy of14.5mJ and1731nm four-order Stokes pulse energy of2mJ, corresponding to a optical-to-optical conversion efficiency of21.7%and a slope efficiency of32.6%, respectively. At the maximum pump pulse energy, the pulse widths for the third-and four-order Stokes pluse were8.6ns and5.2ns, respectively.(Chapter5)The main innovations:1. The characteristics of the α-BaTeMo2O9Raman spectra were systemically studied: the classfication of the lattice vibration mode; the calculation of the Raman scattering coefficiency; relationships between Raman vibration peak and atom vibration group.2. The polarized Raman spectra have been measuremented with different Raman configuration and the steady-state Raman gain coefficient was calculated to be2.4cm/GW@1.06μm.3. We firstly demonstrated a first-order Stokes Raman laser based on a novel α-BaTeMo2O9crystal. The maximum first-order Stokes laser single pulse energy of15.1mJ and output power of2.7W were ontained, respectively, with different pump conditions.4. The performance of second-and third-order Stokes dual-wavelength Raman laser was investigated, with the second-order Stokes output pulse energy of20.1mJ and the third-order Stokes pulse energy of7.2mJ.5. With optimum resonator design, a maximum pulse energy of14.5mJ at1.5μm and2mJ at four-order Stokes wavelength1731nm laser was achieved, with a optical-to-optical conversion efficiency and a slope efficiency of21.7%and32.6%, respectively. |
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