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Research Of High-Power All-Solid-State Green Laser

Posted on:2008-08-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y P ZhangFull Text:PDF
GTID:1118360245990865Subject:Physical Electronics
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All-solid-state lasers (Laser diode-pumped solid-state lasers) have many advantages, such as compact, efficient, good beam quality, stable and long lifetime et al. With the development of laser technology, they have been widely used in the fields of industry, military, medical treatment and research, and have become the mainstream of lasers in application. High-power LD pumped green laser has become the research focus because its important application in material processing, medical application and laser isolation of uranium isotopes, etc. This doctoral dissertation focuses on theoretical and experimental research of high-power all-solid-state 1342nm, 1064nm, quasi-continuum and continuum 532nm lasers.The main contents and key creation points of this dissertation are as follows:(1) A compact, efficient and high-power diode-laser single-end-pumped Nd:YVO4 laser with continuous-wave emission at 1342nm is investigated. A coupling system with a large working spot size of 800μm, a low-doping Nd:YVO4 crystal and reasonable designed resonator are used in the experiments. And we obtained an output power of 7.36W, corresponding to an optical-to-optical efficiency of 32.8%. The laser operates in a nearly TEM00 mode with small amplitude noise of 0.3%(rms). This represents, to the best of our knowledge, the highest power obtained from a diode-laser single-end-pumped Nd:YVO4 continuous wave laser at 1342nm so far and the power stability keep ahead in the world.(2) We investigate the effect of distance between two rods of a double laser-head plane-parallel resonator on stability and beam quality. The results show that, in a thermal-birefringence compensation scheme, low M2 value can be achieved when each rod is, respectively, placed near each laser mirror. And we find that the distance between two inner principal planes of two rods should be near the sum of the thermal focal lengths to compensate a thermal birefringence as well as to get high power without optical damage. In symmetrical plane-parallel two-rod resonator with 90°optical rotator, the thermal birefringence compensation breaks the symmetry of the resonator configuration, which is due to the slight difference between the thermal focal lengths of the radial (fr) and the tangential (fφ) directions of a laser rod. This generates a narrow unstable region inside a stable region, which means a laser power drop in the unstable region as increasing the electric pump power. We propose a method to eliminate the narrow unstable region of a symmetric two-rod resonator with a 90°optical rotator which is used to compensate for thermal birefringence of the laser rod. Using the g-diagram analysis, we find that the narrow unstable region can be removed in the resonator configuration of a symmetric confocal type. We investigate the effect of the distance between two rods of the proposed resonator on the stability and the beam quality.(3) Using a ray matrix method, the resonator stability conditions are analyzed graphically in the symmetric and asymmetric configuration for a plane-parallel resonator. On the basis of an analysis of the stability condition and mode size for the r andφpolarization, we clarify how the stable laser operation is possible for various resonator configurations. Experimentally, the output power characteristics are confirmed in association with the resonator stability. We also analyze theoretically how the r andφpolarization affect the resonator stability condition of two laser heads with or without thermal birefringence compensation. The resonator stability condition is analyzed graphically for a plane-parallel resonator. The maximum range of stable region is found for both the short and the long cavity. The characteristics of the laser output power are confirmed experimentally in association with the resonator stability condition. The laser output power of 482.3W is obtained with the optical-to-optical efficiency of 40.2% for a plane-parallel resonator with a short crystal separation.(4) We analyzed the diffraction efficiency of Acousto-Optic Q-switch (A-O Q-switch) in different cases by solving the coupled wave equation in the medium. And we introduced working principles of several new types of A-O Q-switches. We solved the A-O Q-switched laser rate equations of intracavity frequency-doubled lasers with Runge-Kutta method, obtained optimum length of frequency-doubled crystal, the relation between the optimum length of frequency-doubled crystal and the pump level, the cavity loss. This is the basic of the high power A-O Q-switched green laser.(5) Use 50W, 150W side-pumped laser modules, we investigated single-rod and double-rod A-O Q-switched intracavity-doubled lasers. Using a 50W module, we obtained a green average power of 31.2W with 7 kHz repetition, with optical-to-optical conversion efficiency of 17.3% and power instability of less than 1%. With two 50W modules in tandem with each other, we obtained an average power of 56W at 532nm with 9 kHz repetition, of which the optical-to-optical conversion efficiency is 15.6%, and the power instability is less than 1%. Using the 150W pump module with KTP crystal, we obtained 68.3W green output power. Using the same module with LBO crystal, we obtained 66.6W green output power with optical-optical conversion efficiency of 18.2%. The experiments have been developed into products of 20W and 40W green lasers, the whole performance keep ahead in our country.(6) Research on high power continuum wave (CW) green laser. With an LD side-pumped configuration and three mirror folded cavity design, we obtained 20.7W and 22.7W CW 532nm output power with the pump modules from Beijing GK Laser Technology Co. Ltd. and Wuhan Sapo Laser Industry LTD., respectively. The power instability is about 1%. This can satisfy the demand of CW green laser in laser color display field. This represents, as far as we know, the highest power of CW 532nm output power in our country. And in traditional laser with rod material, this output power is advanced in the world.
Keywords/Search Tags:all solid state, high power, 532nm green laser, intracavity frequency-doubled, A-O Q-switched, CW
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