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Study On High Power And High Beam Quality Solid-State Slab Laser

Posted on:2011-12-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:S ZhaoFull Text:PDF
GTID:1118360302499797Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
The solid-state lasers with high beam quality and high power have been one of laser research focus because of important applications in industry, national defense, medical treatment, environmental protection and scientific research. Slab laser, especially diode-laser partially-end-pumped slab laser (InnoSlab), is one of the most efficient ways to generate powerful laser output with excellent beam quality because of predominant thermal conduction. Compared to the traditional slab lasers, InnoSlab holds two remarkable characteristics:One is partially end-pump. The pumping beam is reformed into a thin rectangular cross-section with symmetrical intensity distribution and then incident into the crystal. However, the pumping beam fills not whole but part of crystal and generates a thin sheet gain layer in the central of crystal, which improves the optical conversion efficiency; The other is hybrid resonator. In the thick direction of crystal, pump beam achieves a good match with laser mode volume because of the small Fresnel number, and then the high beam quality laser can be obtained only by using stable resonator. In the width direction of crystal, an off-axis confocal unstable resonator, which has a good role in selecting mode, is used to obtain nearly diffraction limited beam quality.In this thesis, the continuous wave (CW) of 1.06μm and 1.3μm are achieved based on stable resonator and InnoSlab with diode-laser stack pumped Nd:YVO4 crystal; Inserted acousto-optic Q-switcher and saturable absorber Cr4+:YAG, pulse wave laser properties at 1.06μm and 1.3μm with stable and hybrid resonator are also investigated; Meanwhile, we research the quasi-phase green laser features using periodically poled lithium tantalite (PPLT) crystal with stable resonator. At the seam time, we also establish the theoretical model of CW, active and passive Q-switch with stable resonator. The main researches of this thesis are summarized as follows:I First of all, we introduce the characteristics of waveguide coupling system. Then based on the steady-state heat conduction equation, the temperature gradient and thermal induced stress of the doping concentration of 0.3 at.% Nd:YVO4 crystal are numerical calculated, and thermal stress changing with the pumping power of a single crystal at the center and two end of pumping region are investigated, meanwhile, pump power which the crystal can bear is calculated.II Secondly, for the first time, we establish the rate equations of CW, acousto-optic Q-switch pulse wave and Cr4+:YAG passively Q-switched pulse wave based on a stable resonator. The relationgships between output power, pulse width, single pulse energy, peak power and pumping power are simulated, meanwhile, threshold, slope efficiency and the shortest pulse duration are calculated by the rate equations, and compared with experimental data, the experimental results agree well with theoretical calculations.III Thirdly, the characteristics of partially end-pumped Nd:YVO4 slab laser with stable resonator are researched in the experiment initially. The CW and Q-switch pulse wave are obtained at 1.06μm and 1.34μm. In continuous operation mode, the highest output power 22.5 W of CW laser at 1.06μm is got, and the experimental results agree well with theoretical calculations. Then for the first time, nonlinear crystal PPLT is used in the slab laser because of good match between the nonlinear crystal shape and the pattern of fundamental frequency laser, and the green laser output of 3.05W is realized. Meanwhile, the highest 28.6 W of CW laser output at 1.34μm is obtained; In acousto-optic Q-switch operation mode at 1.06μm, the highest average output power of 68 W of pulsed laser is obtained at the repetitive frequency of 25 kHz with pulse width of 102 ns, corresponding to the maximum conversion efficiency of 40%. For the first time, the acousto-optic Q-switch is inserted to the partially end-pumped Nd:YVO4 slab laser with stable resonator to generate 1.34μm, the maximum average output power of 14 W is obtained with pulse width of 133 ns and repetitive frequency of 10 kHz. Used Cr4+:YAG,1.06μm pulse laser is realized, corresponding to the maximum power of 8.2 W, the shortest pulse width of 166 ns, repetition rate of 255 kHz and peak power of 130 W.IV Fourthly, the characteristics of partially end-pumped Nd:YVO4 slab laser with InnoSlab are investigated. The high power and high beam quality CW is obtained at 1.06μm and 1.34μm too. Used positive branch unstable hybrid resonator, 74 W of CW at 1.06μm is obtained with an M2 factor of 1.2 in the slow direction and 1.3 in the fast direction, which gives slope efficiency and optical conversion efficiency of 50% and 43.5%. Using Fast Fourier-Transform(FFT) method, we simulate the output laser field, the beam shape is in accordance with what we have measured in experiment; Used positive branch unstable hybrid resonator,19.9 W of CW atl.34μm at pumping power of 122.8 W is obtained with an M2 factor of 1.5 in the slow direction and 1.3 in the fast direction. Meanwhile, the maximum output power of 22.4 W is achieved with negative branch unstable hybrid resonator, corresponding to slope efficiency and optical conversion efficiency is 23.4% and 18.2% with an M2 factor of 1.2 in the slow direction and 1.3 in the fast direction.V Fifthly, the characteristics of high power and high beam quality Q-switch pulse wave laser with InnoSlab are investigated. When acousto-optic Q-switch is inserted to positive branch unstable hybrid resonator,61.6 W of CW at 1.06μm laser is obtained with an M2 factor of 1.2 in the slow direction and 1.3 in the fast direction, corresponding to slope efficiency, optical conversion efficiency and pulse width of 41.6%,36.2% and 18.7ns. For the first time, used saturable absorber Cr4+:YAG as passive Q-switch, we achieve the maximum output power of 6.2 W pulse laser at 1.06μm; For the first time, the pulse laser at 1.34μm is realized with acousto-optic Q-switch and negative branch unstable hybrid resonator. when the repetition rate is 10 kHz and the pumping power is 170 W, the maximum average output power of pulse laser of 21.6 W is realized with an M2 factor of 1.2 in the slow direction and 1.3 in the fast direction, corresponding to the single pulse energy of 2.16 mJ, the peak power of 21 kW and the shortest pulse width of 103 ns.The main innovations of this thesis are generalized as follows:I For the first time, the rate equations of CW laser, active Q-switch and passive Q-switch with a stable resonator are established. Then basing on the rate equations, in continuous mode, we simulate the trend of output power changing with pumping power, and calculate the pump threshold and slope efficiency; In Q-switch mode, we calculate the shortest pulse width, and simulate the trend of single pulse energy, we simulate the relationship of repetition rate and pulse width fluctuating with pumping power. Mainwhile, the experimental equipment is built to verify the theory, and the experimental results agree well with theoretical analysis.II For the first time,1.3μm pulse laser with high benm quality is obtained by acousto-optical Q switcher with slab laser. The maximum average output power of 14 W is realized at the repetition rate of 10 kHz with stable resonator, the pulse duration, the single pulse energy and the peak power are 133 ns,1.4mJ and 10.5kW, respectively. With the hybrid resonator, the maximum average output power of 21.6 W with an M2 factor of 1.2 in the slow direction and 1.3 in the fast direction is realized at the repetition rate of 10 kHz. The corresponding pulse duration is 103 ns with single pulse energy of 2.16 mJ and peak power of 21 kW.ⅢFor the first time, Cr4+:YAG is used slab laser to realize pulse laser at1.06μm. The maximum output power of 8.2 W is realized at the repetition rate of 255 kHz with stable resonator, the pulse duration and the peak power are 166 ns and130W, respectively; With the hybrid resonator, the maximum average output power of 6.2 W is realized.IV The CW green laser is realized by PPLT with stable resonator, the output power is 3.05W.
Keywords/Search Tags:partially end-pumped, Nd:YVO4 crystal, slab laser, hybrid resonator, diode -laser stack, 1.06μm, 1.34μm
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