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Study On High Power DPSSL355nm Ultraviolet Lasers

Posted on:2013-01-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:B T ZhangFull Text:PDF
GTID:1118330374980706Subject:Condensed matter physics
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Recently, the development and applications of the all-solid-state ultraviolet (UV) lasers have been attracted much attention. Compared with the traditional excimer UV lasers, all-solid-state UV lasers have the advantages such as better beam quality, more compact, higher efficiency, longer lifetime, non-toxic, do not need to change special gas and so on. Infrared (IR) or visible laser processing is optical thermal working, in which laser processing produce concentrated heating material for melting or gasification. The thermal effect makes material deformation and coking form damage in cutting or drilling edge. Therefore, it's difficult to achieve the fine and smooth result, and easy to cause fracture for ceramic and wafer processing. But UV laser processing is optical cold working, during which the high-energy photons of UV lasers can directly interrupt chemical bond of the materials. The UV laser beam and material interact to produce the photon melting process, to avoid the long wavelength pulse of the defects caused by heat and insufficiency. Therefore, UV laser processing is particularly advantageous for fine processing to SiC, GaN etc broadband gap semiconductor material, carbon polymers and ITO thin film. In Germany, USA, Japan and other developed countries, UV laser has become a standard industrial laser.355nm UV laser with average output power of5-10W have been reached practical level and successfully used for laser scribing, broadband gap semiconductor materials marking, laser processing and subtle drilling. Solid-state UV laser at present already have been widely applied in the fields such as semiconductor industry, material preparation, all the light optical device production, integrated circuit board and biological engineering, etc.In this dissertation, by using the all-solid-state lasers, we have theoretically and experimently studied the output charecters of intracavity frequency tripled355nm lasers. The rate equations have been established to guide the experiments for the laser diode end pumped intracavtiy frequency tripled lasers. Based on the experiments, we have developed the high power355nm UV laser processing system with output power of5W. The355nm UV laser processing system has been successfully used for laser marking on the SiC semiconductor material and for the surface texturing on Ga-polor p-GaN surface. The patterns created on p-GaN are confirmed to be suitable for light extraction and a34.9%enhancement of the electroluminescent (EL) emission intensity has been obtained. This method could be extended to other Ⅲ-Ⅴ LEDs and LEDs on SiC for fabricating highly efficient LEDs. The main content of this dissertation includes:1. By considering the nonlinear frequency conversion as the loss for the fundamental wavelength, the rate equations for the intracavtity frequency tripled lasers, including AO Q-switched and passively Q-switched lasers, have been established under the large and small signal approximation, respectively.(Chapter2)2. The compact efficient diode-end-pumped acousto-optically Q-switched intracavity frequency-tripled355nm UV lasers have been realized by using Nd:YVO4and Nd:YAG as the laser medium, respectively. We compared the UV laser output characters with and without the second harmonic mirrors. The relationship between the average output power and the absorbed pump power for several freuencey repetion rates was studied to confirm the optimum repetition rate of AO Q-switch. The average output power, pulse width, the power stability and the laser beam profile have been measured. By considering the the SHG and THG process as the nonlinear loss, under the large signal approximation, the rate equations of the AO Q-switched intracavity frequency tripled lasers was numerically calculated. The experimental results were in good with the theoretical results, which confirmed the applicability of the theoretical modeal.(Chapter3)3. The intra-cavity frequency-tripled diode-end-pumped passively Q-switched Nd:YAG/Cr4+:YAG composite laser has been investigated. The relationships between the average output power, the pulse width, the repetition rate and the absorbed pump power were measured. The beam quality and power stability were also measured and presented. The rate equation model of the intracavity frequency tripled passively Q-switched laser was proposed. The results of numerical calculations of the rate equations are in good agreement with the experimental results.(Chapter3)4. The laser output performances of the fundamental wave at1.06and1.3μm for high power Nd:YAG module was firstly investigated. A comparative study of the high power intracavity frequency doubling532nm laser based on C-KTP, GTR-KTP and LBO crystals was also presented. In addation, the high power red laser based on the intracavity SHG with LBO crystal was also realized.(Chapter4)5. By using C-KTP, GTR-KTP and LBO crystals respectively as the SHG crystal and CBO, LBO crystals as the SFG crystals, the high power355nm UV generated by intracavity frequency tripled Nd:YAG module was studied. Based on the comparative study, the optimum SHG and SFG crystal combination was found to be C-KTP and LBO. The optimum AO Q-switch repetition rate was confirmed, under which the average output power, the pulse width and the power stability was measured with the optimum crystal combination. The beam quality was also presented.(Chapter4)6. Based on the experimental results of7.8W high power355nm UV laser in Chapter4, an UV laser processing system named ICM-UV-1with5W ouput power has been developed. The basic parameters of the electocircuit, waterway, scanlens, the average output power, pulse width, power stability as well as the scanning speed were presented. The system was successfully used for laser marking on SiC semiconductor metarial. The width, depth and the string size of the marking SiC were tested and compared with systems from the advanced companies. The results indicated that our system could meet the requirement for the industry laser processing. For the first time, to our knowledge, a pulsed UV laser in combination with a mirror scanner was used for the surface texturing Ga-polor p-GaN surface improve the light extraction efficiency of GaN based blue light emitting diodes (LEDs) The patterns created on p-GaN were confirmed to be suitable for light extraction and a34.9%enhancement of the electroluminescent (EL) emission intensity has been obtained. Detailed discussions on the effects of laser on LEDs and the angular dependence of the emission profile were also provided. This method could be extended to other Ⅲ-Ⅴ LEDs and LEDs on SiC for fabricating highly efficient LEDs. The experts checked and approved the research and customer application reports, gave a high praise on the system.(Chapter5)The main innovations of this dissertation are as follows:1. Under the small and large signal approximation, the rate equations of AO Q-swithced and passively Q-switched intracavity THG was proposed and numeriacal calculated respectively for the first time.2. The coupled cavtity was established by inserting the second and third harmonic dielectric mirrors into the cavity to improve the THG conversion efficiency. By using the simple linear cavity, as high as7.8W355nm UV laser was generated with C-KTP used for SHG and LBO used for SFG.3. The laser processing system with output power of5W was developed and successfully used for laser marking on SiC semiconductor material.4. For the first time, to our knowledge, a pulsed UV laser in combination with a mirror scanner was used for the surface texturing Ga-polor p-GaN surface improve the light extraction efficiency of GaN based blue light emitting diodes (LEDs) The patterns created on p-GaN are confirmed to be suitable for light extraction and a34.9%enhancement of the electroluminescent (EL) emission intensity has been obtained. This method could be extended to other III-V LEDs and LEDs on SiC for fabricating highly efficient LEDs.
Keywords/Search Tags:all-solid-state, UV laser, rate equations, second harmonic generation, intracavity third harmonic generation, KTP, LBO, UV laser processing system, LEDsurface texturing
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