| Beam characteristic and its thermal stability of the radio frequency-exited waveguide CO2laser are important both in theoretical researches and engineering design. The intra-cavity and output beam characteristics of the RF-excited slab CO2laser which determined by the slab structure have been studied in this thesis. The temperature distribution and the hot distortion of the slab electrodes and the output window are analysed by the finite element method, to find out the impact of the thermal stability on the laser. The wavelength selected RF-excited waveguide CO2lasers is summarized and introduced as a branch application, and a large power grating-waveguide-folded resonator is designed for this laser. The main contents are classified as follows.(1) A positive-branch unstable-waveguide hybrid resonator is designed for the hundred watts level RF-excited slab CO2lasers based on the theory of one-dimensional unstable resonator and waveguide resonator. The output beam modes in these two directions are analyzed with the method of separating variables. The optical field distributions in the near field and the far field and the characteristics of power misalignment are measured experimentally. It is demonstrated that the beam is approximately collimated in the unstable dimension, yet strongly affected by the hard-edge diffraction. Simultaneously, the beam mode is a similar fundamental mode in the waveguide dimension with a big divergence angle.(2) The eigenvector method is extended for unstable resonators combined with the Collins formula and the ABCD ray matrix. In the process of this method there is not any approximation on the aperture sizes of both mirrors. The mode behavior in a resonator with arbitrary irregular structures can be studied exactly and conveniently. An asymmetrical practical unstable resonator and a non-confocal practical unstable resonator are numerically simulated under varying structure parameters, and some new characteristics are found. The loss curves of some lower order modes versus different geometric parameters are obtained.(3) Experiments for the stabilities are taken on a2kW RF-excited slab CO2laser, to investigate how the thermal stability affects the beam characteristics. The steady state temperature distribution on the slab electrodes are simulated with thermodynamics FEM method. The value of the convective heat transfer coefficient, which is a key parameter in the heat convection, is discussed, and several values are tried in the simulations. A transient heat analysis of the slab electrode is taken. The dynamic thermodynamics process from start to stability of some points on the electrode is simulated. It is shown that when the convective heat transfer coefficient is given a higher value, this process will be fast, and when h=2000W(m2·℃) the time is about5min.(4) The heat stress and heat distortion of the slab electrodes and the output window are analyzed with FEM. Three different fixing structures of the electrodes are designed and analyzed. It is proven that the insulating ceramics fixing method and the free fixing method without restriction are both suitable, and the later method is more advanced for the electrodes with large area. The impact of the output beam of the unstable-waveguide hybrid resonator on the output window is researched. A distribution function of the laser power is composed with polynomial fitting in the FEM simulation. And then, the thermal lens effect of the output window under a high laser beam is studied.(5) Some technologies of the wavelength selected CO2laser are summarized, such as the actuating medium, the level structures, the tuning method with grating and so on. The development and the key technologies of the tunable RF-excited slab CO2laser are discussed. A special grating-waveguide-folded resonator is designed for the high power tunable slab CO2laser, and mode behaviors are researched. For a grating resonator, the mode and misaligned characteristics under different Liitrow angle are studied systematically. |
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