【作者】 李明；

【导师】 赵圣之；

【作者基本信息】 山东大学 ， 光学工程， 2009， 博士

【摘要】 激光二极管泵浦的全固态激光器因具有结构紧凑、效率高、热效应小、稳定性高、寿命长、光束质量好、工作介质覆盖的波段范围广及运转方式多样化等优点,在材料加工、军事、医疗、空间通讯、光显示、光互联、光信息处理和科研等领域得到广泛的应用,成为目前激光领域的研究热点。激光晶体增益介质是激光器的核心部件,它的光谱和物理特性决定了激光器系统的整体设计和输出特性。其中掺钕离子的激光晶体由于吸收波长在808nm附近,适合于半导体激光器抽运,作为增益介质得到了广泛研究。本论文采用光纤耦合输出的激光二极管作泵浦源,用Nd:YVO₄、Nd:GdVO₄和Nd:LuVO₄晶体作为激光工作物质,利用Cr:YAG、LT-GaAs、SESAMs和V:YAG的饱和吸收特性,分别实现了1.06μm和1.34μm波段的调Q锁模激光运转;用Nd:GdVO₄晶体作为激光工作物质和克尔介质,实现了Nd:GdVO₄自锁模激光运转;利用KTP的二阶级联非线性（cascaded second-ordernonlinearity）和倍频特性实现了绿光自调Q锁模激光运转;用声光Q开关（AO）作为稳定元件,分别实现了Nd:GdVO₄ 1.06μm和Nd:GdVO₄/KTP 0.53μm主动调Q锁模激光运转;利用AO-Cr:YAG组合研究了主被动双调Q锁模激光的脉冲输出特性;同时,运用高斯近似下的速率方程组对以上调Q锁模激光的运转特性进行了理论模拟。论文的主要研究工作包括:Ⅰ分析了Cr:YAG可饱和吸收体的调Q锁模原理,利用光强起伏机制及调Q速率方程模型,给出了高斯分布近似下描述Cr:YAG调Q锁模运转特性的速率方程组;在折叠腔内实现了LD泵浦c-cutNd:GdVO₄ 1.06μm及KTP腔内倍频0.53μm激光运转,并利用调Q锁模速率方程组模拟了该激光器的动力学过程。（§2.2）Ⅱ采用LD泵浦Nd:GdVO₄晶体,以V:YAG晶体为可饱和吸收体,实现了三镜折叠腔1.34μm调Q锁模激光运转,研究了1.3μm调Q锁模激光的输出特性;利用可饱和吸收体调Q锁模模型,在高斯分布近似下给出了描述V:YAG调Q锁模运转特性的速率方程组,数值模拟与实验结果相符。（§2.3）Ⅲ采用三镜折叠腔结构,以LT-GaAs为可饱和吸收体,实现了LD泵浦Nd:LuVO₄1.06μm及Nd:GdVO₄/KTP腔内倍频0.53μm被动调Q锁模激光运转;考虑GaAs双光子吸收,给出了高斯分布下描述LT-GaAs被动调Q锁模运转的速率方程组,并利用该模型对实验结果进行了理论模拟。（§3.2）Ⅳ以中间镜式SESAMs为可饱和吸收体,实现了LD泵浦被动调Q锁模Nd:GdVO₄/KTP腔内倍频0.53μm光运转;考虑SESAMs可饱和吸收体的饱和损耗,给出了高斯分布下描述SESAMs被动调Q锁模运转的速率方程组,数值求解所得结果与实验结果相符。（§3.3）Ⅴ实现了自调Q自锁模Nd:GdVO₄激光运转,在折叠腔内没有任何额外元件的情况下,得到了较稳定的激光脉冲输出;把c-cut Nd:GdVO₄激光晶体和软光阑等效为快饱和吸收体,考虑克尔介质的非线性传输矩阵,根据光束在光腔内往返传播的ABCD法则和光强起伏机制,给出了克尔透镜锁模激光脉冲输出性能的速率方程模型,得到了与实验结果近似的理论计算值。（§4.2）Ⅵ考虑KTP的二阶级联非线性特性的影响,并考虑激光晶体的克尔效应,建立了描述LD泵浦Nd:GdVO₄腔内倍频绿光自调Q自锁模运转特性的速率方程新模型;实验上分别实现了LD泵浦α-cut和c-cut Nd:GdVO₄/KTP自调Q自锁模0.53μm激光运转,数值求解Nd:GdVO₄/KTP自调Q自锁模速率方程组所得的理论值与实验结果基本相符。（§4.3）Ⅶ利用声光调Q开关,考虑Nd:GdVO₄晶体的克尔效应和声光开关的关断时间对脉冲特性的影响,在高斯分布近似下建立了描述克尔锁模激光运转特性的速率方程模型;实验上利用折叠腔实现了Nd:GdVO₄/AO 1.06μm和Nd:GdVO₄/AO KTP腔内倍频0.53μm自调Q锁模激光的稳定运转,测量了不同声光调制频率下,激光平均输出功率、脉冲能量等随泵浦功率的变化关系,数值求解Nd:GdVO₄基频和KTP倍频自调Q自锁模速率方程组所得的理论值与实验结果近似。（§5.1、§5.2）Ⅷ实现了LD泵浦Nd:GdVO₄晶体AO-Cr:YAG主被动调Q锁模激光运转,通过在激光腔内插入一个声光调制器,Nd:GdVO₄被动调Q锁模激光器的稳定性得到了很好的加强,测量并比较了声光调制器打开前后两种状态下的激光特性;考虑声光关断时间及调制频率的影响,给出了描述主被动双调Q锁模激光运转特性的速率方程模型,数值求解方程的理论计算值与实验结果相符。（§5.3）论文的主要创新工作包括:Ⅰ首次给出了高斯分布近似下Cr:YAG调Q锁模速率方程理论,并首次实现了LD泵浦c-cut Nd:GdVO₄晶体Cr:YAG调Q锁模1.06μm和KTP内腔倍频0.53μm激光运转,理论模拟与实验结果相符。Ⅱ利用KTP作为倍频晶体,首次对LD泵浦c-cut Nd:GdVO₄晶体、LT-GaAs被动调Q锁模绿激光运转特性进行了系统的理论和实验研究;利用高斯分布近似下的速率方程模型,给出了LT-GaAs调Q绿光锁模速率方程理论模型,理论模拟结果重现了调Q锁模运转的输出特性。Ⅲ首次实现了Nd:GdVO₄自锁模激光的稳定运转:利用声光调Q开关,得到了稳定的锁模脉冲,考虑Nd:GdVO₄晶体的克尔效应和声光开关的关断时间对脉冲特性的影响,在高斯分布近似下建立了描述克尔锁模激光运转特性的速率方程模型,数值求解方程的理论计算值与实验结果相近。Ⅳ首次考虑KTP的二阶级联非线性特性的影响,和激光晶体的克尔效应,建立了描述LD泵浦Nd:GdVO₄腔内倍频绿激光自调Q自锁模运转特性的速率方程新模型,理论分析与实验结果基本相符。Ⅴ首次实现了LD泵浦Nd:GdVO₄晶体AO-Cr:YAG主被动调Q锁模激光运转,考虑腔内光子数密度、激活介质反转粒子数密度和泵浦光的横向与纵向分布和声光关断时间及调制频率的影响,给出了描述双调Q锁模激光运转特性的速率方程模型,得到了与实验结果相符的理论计算值。Ⅵ首次实现了LD泵浦Nd:GdVO₄晶体三镜折叠腔V:YAG调Q锁模1.34μm激光器运转,并利用高斯近似下的调Q锁模速率方程模型进行理论模拟,得到的计算结果与实验结果基本相符。更多还原

【Abstract】 Laser diode-pumped all-solid-state lasers have a compact structure,high efficiency, small heat effect,high stability,long life-time,high beam quality,wide wavelength range and various running modes.Due to the advantages,these kinds of lasers have a wide range of applications in the fields such as materials processing,military,medical,space communications,light display,optical interconnection,information processing and scientific research fields,laser telecommunication,light display and so on.Laser crystal is the core component in laser system.Its physical and spectra properties determine the global design and output characteristics of the laser system.The Nd-doped crystals due to their excellent lasing property and availability of direct laser diode pumping have been widely used to construct compact laser-diode pumped solid-state lasers in the near-infrared region.In this dissertation,by using the fiber-coupled laser-diode as the pump source,Nd:YVO₄,Nd:GdVO₄,and Nd:LuVO₄ crystals as the gain media,we have studied the performance of the passively Q-switched mode-locked（QML） lasers at 1.06μm and 1.34μm with Cr:YAG,LT-GaAs,SESAMs as well as V:YAG saturable absorbers,respectively.The research on the frequency doubling performance of the KTP crystal in the passively QML lasers has been carried out.Considering the Kerr-lens effect of Nd:GdVO₄,the diode-pumped self-passively QML Nd:GdVO₄ lasers have also been obtained and the characteristics have been studied.Using the cascading of second-order nonlinearities of KTP crystal, diode-pumped self-passively QML intracavity frequency doubled Nd:GdVO₄/KTP green laser is obtained.In addition,we studied the actions of acoustic-optic（AO） modulator in self QML Nd:GdVO₄ laser,self QML Nd:GdVO₄/KTP green laser and QML Nd:GdVO₄/Cr:YAG laser,respectively.Meanwhile,the coupling rate equations under Gaussian wave approximation have been estabilished to theoretically analyze the properties of the above-mentioned QML lasers.The main contents of this dissertation include:ⅠThe principle of the simultaneously Q-switched and mode-locked lasers has been presented first,then using the indensity fluctuation mechanism and the rate equations model for the Q-switched lasers,the rate equations describing the simultaneously Q-switched and mode-locked lasers under Gaussian distribution approximation have been given.A diode-pumped simultaneously Q-switched and mode-locked c-cut Nd:GdVO₄ 1.06μm and 0.53μm laser with Cr:YAG crystal have been realized in the experiment,and the dynamic process of such lasers have been simulated by using the proposed mode-locking rate equations model.（§2.2）ⅡUsing aⅤ-type cavity,a diode-pumped passively Q-switched and mode-locked Nd:GdVO₄ 1.34μm laser with V:YAG crystal as the saturable absorber is realized.The characters of the laser have been studied.Using the passively QML model under Gaussian distribution approximation,a couple of rate equations describing the passively QML laser with V:YAG are given.The numerical solution is consistent with the experimental results. （§2.3）ⅢBy employing a 1.06 m three-mirror-folded cavity configuration,LT-GaAs as the saturable absorber,a diode-pumped passively QML Nd:LuVO₄ 1.06μm and Nd:GdVO₄ 0.53μm green lasers are realized.Considering the two-photon absorption of GaAs,a couple of rate equations under Gaussian distribution approximation describing the passively QML laser with LT-GaAs are given.And the dynamic process of such laser has been simulated by using the proposed mode-locking rate equations model.（§3.2）ⅣUsing SESAM as an intracavity saturable absorber,we obtained the performance of a diode-pumped passively Q-switched and mode-locked Nd:GdVO₄ laser at 532 nm.Using the hyperbolic secant function methods,we have introduced a rate equation mode for the QML SESAM green laser,in which the Gaussian distribution of the intracavity photon lifetime of the active medium,the excited-state lifetime of the saturable absorber and the effective average loss of SESAM were taken into account.With this model,the theoretical evaluations are in good agreement with the experiments.（§3.3）ⅤA steadily self-Q-switched and mode-locked diode-pumped c-cut Nd:GdVO₄ laser without inserting any additional intra-cavity element has been observed.Considering the Kerr-lens effect of laser medium and the soft aperture induced by the distribution of pump beam in the laser medium,we have analyzed the self-mode-locked c-cut Nd:GdVO₄ laser by using the nonlinear ABCD propagation matrix and the hyperbolic fluctuation mechanism.The numerical solutions are in good agreement with the experimental results.（§4.2）ⅥConsidering the cascading of second-order nonlinearities of KTP crystal,and also the influences of Kerr-lens effect of laser crystal,a developed rate equation model for self QML lasers was proposed.A diode-pumped self a-cut and c-cut Nd:GdVO₄/KTP green laser is realized in the experiment,and the dynamic process of such laser has been simulated by using the proposed mode-locking rate equations model.（§4.3）ⅦUsing the AO modulator and considering the Kerr-lens effect of Nd:GdVO₄ crystal and the turn-off time of AO Q-switch,a rate equation model under Gaussian distribution approximation describing the Kerr-lens QML laser is given.By using three-mirror-folded cavity,a diode-pumped Nd:GdVO₄/AO 1.06μm and Nd:GdVO₄/AO KTP 0.53μm green laser have been realized in the experiments.For different repetition rates,the laser properties such as average output power and pulse energy have been measured.The numerical solutions are in good agreement with the experimental results.（§5.1、§5.2）ⅧThe experimental studies on the diode-pumped doubly Q-switched and mode-locked Nd:GdVO₄ laser with AO and Cr:YAG have been carried out.By inserting an acousto-optic modulator inside the laser cavity,the stability of the Q-switched and mode-locked Nd:GdVO₄ laser was significantly increased.The laser properties when the AO modulator turn on and turn off were both reached.By considering the influence of the turnoff time and the modulation frequency of the acousto-optic modulator,we proposed a developed rate equation model for actively-passively Q-switched and mode-locked lasers.With this developed model,the theoretical calculations are in good agreement with the experimental results.（§5.3）The main innovations of this dissertation are as follows:ⅠWe firstly develop a rate-equation model for the diode-pumped under Gaussian distribution approximation,and we firstly realize the operation of the diode-pumped simultaneously Q-switched and mode-locked c-cut Nd:GdVO₄ 1.06μm and 0.53μm with Cr:YAG saturable absorber.The numerical analysis is consistent with the experimental results.ⅡBy employing KTP as the frequency doubling crystal,we firstly study the experimental and theoretical operation of the diode-pumped simultaneously QML c-cut Nd:GdVO₄/KTP LT-GaAs green laser.Using a couple of rate equations describing the dynamic process of the QML green laser with LT-GaAs,and the theoretical simulation reconstructs the output pulse of the mode-locked laser.ⅢUsing the AO modulator,we firstly realize a steadily self QML diode-pumped Nd:GdVO₄ laser.Considering the Kerr-lens effect of laser medium,the influence of the turnoff time and the modulation frequency of the acousto-optic modulator,we proposed a developed rate equation model for Kerr-lens QML lasers.With this developed model,the theoretical calculations are in good agreement with the experimental results.ⅣBy considering the cascading of second-order nonlinearities of KTP crystal and the Kerr-lens effect of laser medium in the dynamic process of the self QML laser,a rate equation model is build up to describe diode-pumped intracavity frequency doubling Nd:GdVO₄/KTP green laser operating in QML.The numerical analysis is consistent with the experimental results. ⅤWe firstly realize a diode-pumped actively-passively QML Nd:GdVO₄ laser with Cr:YAG and AO modulator.Meanwhile,using the hyperbolic secant function methods and by considering the influence of the turnoff time and the modulation frequency of the acousto-optic modulator,we proposed a developed rate equation model for actively-passively Q-switched and mode-locked lasers.With this developed model,the theoretical calculations are in good agreement with the experimental results.ⅥWe firstly present systematically theoretical and experimental studies on the laser properties of diode-pumped Nd:GdVO₄/V:YAG 1.34μm laser operating in QML by using aⅤ-type cavity.Using the hyperbolic secant function methods,we have introduced a rate equation mode for the 1.34μm QML laser,in which the Gaussian distribution of the intracavity photon lifetime of the active medium,the excited-state lifetime of the saturable absorber are taken into account.With this model,the theoretical evaluations are in good agreement with the experiments.更多还原