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Optimization Of The Key Parameters Of All Solid-state Q-switched Lasers

Posted on:2008-07-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:D C LiFull Text:PDF
GTID:1118360212494420Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Laser-diode (LD) pumped all solid-state Q-switched laser has wide applications in the fields such as laser telecommunication, remote-sensing detection, industry and military as well as healthy due to its advantages such as all solid state, high pump efficiency, small volume and long longevity, and has been paid much attention on.In this dissertation, by using the new rate-equation model, we have theoretically studied the characteristics of the LD-pumped all solid-state Q-switched lasers. We have studied the performance of the output pulse in the passively Q-switched lasers with Cr4+-doped saturable absorbers and GaAs saturable absorbers, and in the actively Q-switched lasers with acousto-optic (AO) switches, respectively. The performance of the output pulse in the doubly Q-switched lasers with acousto-optic(AO)-Cr4+-doped saturable absorber, AO—GaAs and Cr4+-doped saturable absorber—GaAs have also been studied, respectively. Besides, the research on the optimization of the output energy, the peak power and the pulse width in the above-mentioned Q-switched lasers has been carried out, and the optimal results are in agreement with the experimental results. The optimum parameters obtained above can help us in the design of these all solid-state Q-switched lasers.The main contents and the main innovations of this dissertation include:(I) By considering the single-photon and two-photon absorptions of GaAs saturable absorber, we have used the new rate-equation model to analyse the properties of the passively GaAs Q-switched laser. And using the technique of Lagrange multipliers, we have determined the key parameters of an optimally coupled GaAs saturable absorber Q-switched laser based on optimizing the output energy, or based on optimizing the peak power for the first time. The dependence of the optimum output energy and the optimum peak power on different reflectivities of the output mirror and different small-signal transmissions of GaAs have been obtained. For a given pump power with different reflectivities of the output mirror and different small-signal transmissions of GaAs, the pulse energy, peak power and pulse width of a GaAs Q-switched Nd:YVO4 laser have been measured. The optimal results are in agreement with the experimental results.(II) By taking into account turnoff time of the slowly active Q-switch, the coupled equations of a slowly actively Q-switched laser are given for the first time. The key parameters of an optimally coupled actively Q-switched laser with the turnoff time are determined, which maximizes the output energy. The dependence of the optimal output energy on reflectivities of the output mirror have been obtained. In addition, the importance including turnoff time of the slowly active Q-switch is also shown. The corresponding peak power and pulse width have been given. The optimal calculations for an actively Q-switched Nd:YVO4 laser with acoustic-optic modulator are presented to demonstrate the use of the curves and the related formulas.(III) The theoretical and experimental studies on the characteristics in a LD-pumped passively Q-switched laser with Cr4+-doped saturable absorber have been presented. The intracavity photon density and the initial population-inversion density in the passively Q-switched lasers are assumed to be Gaussian spatial distributions. The key parameters of an optimally coupled passively Q-switched laser under Gaussian approximation are determined based on maximizing the output energy, the peak power, or minimizing the pulae width for the first time. The dependence of the optimal parameters on the parameters of the gain medium, the saturable absorber, and the resonator have been obtained. In addition, the importance including the space variation is also shown. For a given pump power with different reflectivities of the output mirror and different small-signal transmissions of Cr4+:YAG, the pulse energy, peak power and pulse width in a Cr4+:YAG Q-switched Nd:YVO4 laser have been measured. The optimal results are in agreement with the experimental results. (IV) The theoretical and experimental studies on the characteristics in a LD-pumped doubly Q-switched laser with both an acousto-optic modulator and a Cr4+-doped saturable absorber have been presented. By considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the acousto-optic (AO) Q-switch, we provide the coupled rate equations for a doubly Q-switched laser with both an AO modulator and a Cr4+-doped saturable absorber. The key parameters of an optimally coupled doubly Q-switched laser are determined for the first time. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the saturable absorber, the AO Q-switch, the resonator and the spatial distributions of the intracavity photon density. Sample calculations for a LD-pumped Nd4+:YVO4 laser with both an AO modulator and a Cr4+:YAG saturable absorber are presented to demonstrate the use of the curves and the related formulas. For a given pump power with different reflectivities of the output mirror and different small-signal transmissions of Cr4+:YAG, the pulse energy, peak power and pulse width in a LD-pumped Nd3+:YVO4 laser with both an AO modulator and a Cr4+:YAG saturable absorber have been measured. The optimal results are in agreement with the experimental results.(V) The theoretical and experimental studies on the characteristics in a LD-pumped doubly Q-switched laser with both an acousto-optic modulator and a GaAs saturable absorber have been presented. By combining the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs saturable absorber, and considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the acousto-optic (AO) Q-switch, we provide the coupled rate equations for a diode-pumped doubly Q-switched laser with both an acousto-optic (AO) modulator and a GaAs saturable absorber. The key parameters of an optimally coupled doubly Q-switched laser are determined for the first time. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the GaAs saturable absorber, the acousto-optic (AO) Q-switch, the resonator and the spatial distributions of the intracavity photon density. Sample calculations for a LD-pumped Nd:YVO4 laser with both an acousto-optic (AO) modulator and a GaAs saturable absorber are presented to demonstrate the use of the curves and the related formulas. For a given pump power with different reflectivities of the output mirror and different small-signal transmissions of GaAs, the pulse energy, peak power and pulse width in a LD-pumped Nd3+:YVO4 laser with both an AO modulator and a GaAs saturable absorber have been measured. The optimal results are in agreement with the experimental results.(VI) The theoretical and experimental studies on the characteristics in a LD-pumped double passively Q-switched laser with both a GaAs saturable absorber and a Cr4+-doped saturable absorber have been presented. By combining the SPA and TPA processes of GaAs saturable absorber, and considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density, we provide the coupled rate equations for a LD-pumped double passively Q-switched laser with both a GaAs saturable absorber and a Cr4+-doped saturable absorber. The key parameters of an optimal double passively Q-switched laser are determined for the first time. The curves clearly show the dependence of the optimal parameters of a double passively Q-switched laser on the parameters of the gain medium, the GaAs saturable absorber, the Cr4+-doped saturable absorber and the spatial distributions of the intracavity photon density. Sample calculations for a LD-pumped Nd3+:YVO4 laser with both a Cr4+:YAG saturable absorber and a GaAs saturable absorber are presented to demonstrate the use of the curves and the related formulas. For a given pump power with different reflectivities of the output mirror, different small-signal transmissions of Cr4+:YAG, and different small-signal transmissions of GaAs, the pulse energy, peak power and pulse width in a LD-pumped Nd3+ YVO4 laser with both a Cr4+:YAG saturable absorber and a GaAs saturable absorber have been measured. The optimal results are in agreement with the experimental results.
Keywords/Search Tags:Cr4+-doped saturable absorbers, GaAs saturable absorbers, Optimization, Double Q-switching, Rate-equation model
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