【作者】 安晶；

【导师】 赵圣之；

【作者基本信息】 山东大学 ， 光学工程， 2009， 博士

【摘要】 全固态短脉冲激光器由于其具有结构简单、泵浦效率高、稳定性强、寿命长、光束质量好等众多优点,使其在激光通讯、遥感探测、光信息处理、激光加工、激光医疗和军事武器装备等领域均有广泛的应用前景,引起人们极大的关注。本论文采用氙灯和光纤耦合输出的半导体激光器作为泵浦源,用Nd:YAG、Nd:YVO₄、Nd:GdVO₄和Nd:LuVO₄晶体作激光工作物质,利用声光开关、饱和吸收体Cr⁴⁺:YAG和GaAs作为腔内调Q元件,研究了声光—GaAs主被动双调Q、Cr⁴⁺:YAG—GaAs双被动调Q激光的脉冲输出特性和脉宽控制特性;利用KTP晶体和周期极化的LiNbO₃（PPLN）晶体作为腔内倍频晶体,研究了双折射相位匹配和准相位匹配绿激光连续及调Q运转特性;运用速率方程对以上调Q、双调Q激光的运转特性进行了理论模拟,理论计算与实验结果相符。论文的主要研究工作包括:Ⅰ实现了氙灯泵浦Nd:YAG晶体、Cr⁴⁺:YAG和GaAs双被动调Q 1.06μm激光运转,测量了单一被动调Q、双被调Q激光的脉冲对称因子和脉冲宽度与输出镜反射率及Cr⁴⁺:YAG小信号透过率的依赖关系。结果表明,与单一Cr⁴⁺:YAG和GaAs被动调QNd:YAG激光相比,双被调Q激光不但脉宽被压缩,而且产生的脉冲形状更加对称。考虑GaAs饱和吸收体的单光子、双光子以及自由载流子吸收过程,运用平面波近似下耦合的速率方程对激光脉冲的输出特性进行了理论模拟,理论计算与实验结果相符。（第二章2.1节）Ⅱ研究了氙灯泵浦Nd:YAG晶体、KTP内腔倍频、Cr⁴⁺:YAG和GaAs双被动调Q0.53μm绿激光特性。测量了单一被动调Q和双被动调Q激光脉冲宽度和脉冲对称因子与Cr⁴⁺:YAG小信号透过率的依赖关系;测量了激光的脉冲宽度、平均输出能量、脉冲重复率随泵浦能量变化规律,获得了输出脉冲的单脉冲能量和脉冲峰值功率随泵浦能量的变化规律;利用平面波近似下耦合的速率方程模型对实验结果进行了理论模拟,数值计算与实验结果相符。（第二章2.2节）Ⅲ实现了LD泵浦c-cut Nd:GdVO₄晶体、声光—GaAs主被动双调Q 1.06μm激光运转,并比较了a轴切割（a-cut）与c轴切割（c-cut）的双调Q Nd:GdVO₄激光输出脉冲的脉冲宽度和峰值功率。实验结果表明,与a-cut Nd:GdVO₄激光相比较,c-cutNd:GdVO₄激光虽然泵浦阈值更高,但具有更窄的脉冲宽度和更高的峰值功率增长率;另外,比较了c-cut Nd:GdVO₄双调Q与单一AO及GaAs调Q激光输出脉冲的宽度、重复率及峰值功率随泵浦功率的变化关系。在理论分析中,讨论了激光晶体的热效应对腔模尺寸和衍射损耗的影响,并将泵浦光近似为一个高斯光束,同时将腔内光子数密度和反转粒子数密度均考虑成高斯分布,给出了描述声光—GaAs主被动双调Q激光运转特性的速率方程模型,对声光和GaAs双调Q激光运转特性进行了理论模拟。（第三章3.1节）Ⅳ从理论和实验上研究了LD泵浦c-cut Nd:GdVO₄晶体、KTP内腔倍频、AO—GaAs主被动双调Q 0.53μm激光的脉宽压缩特性。测量了主被动双调Q、单一AO和GaAs三种调Q激光输出脉冲的上升沿、下降沿的宽度以及脉冲宽度和重复率随泵浦功率的变化,获得了脉冲对称因子、单脉冲能量、峰值功率随泵浦功率的变化关系;结果表明,与单一调Q激光相比,双调Q激光的脉宽明显被压缩,且脉冲对称性提高;并将c-cutNd:GdVO₄双调Q激光与a-cut Nd:GdVO₄双调Q激光KTP内腔倍频时的各种激光特性进行了比较。利用高斯近似下的速率方程模型对实验结果进行了理论模拟,理论计算和实验结果相符合。（第三章3.2节）Ⅴ采用三镜折叠腔结构,实现了LD泵浦Nd:YVO₄晶体、KTP内腔倍频、Cr⁴⁺:YAG和GaAs双被动调Q 0.53μm绿激光运转,给出了三种不同Cr⁴⁺:YAG小信号透过率下的双调Q激光的平均输出功率、脉冲宽度、单脉冲能量和峰值功率随泵浦功率的变化关系;比较了双被动调Q与单一Cr⁴⁺:YAG和GaAs被动调Q情况的下的脉冲宽度与脉冲对称因子。当Cr⁴⁺:YAG小信号透过率T₀=71%时,双调Q激光的平均输出功率最大。这说明双调Q激光的输出特性与两种饱和吸收体的小信号透过率有关;与单一被动调Q激光相比,双被动调Q脉冲激光不仅能压缩脉宽、提高脉冲对称性,而且输出的单脉冲能量和峰值功率得到提高。（第三章3.3节）Ⅵ简单介绍了Nd:YVO₄/YVO₄键合激光晶体的制造过程及性质,实现了LD泵浦Nd:YVO₄/YVO₄晶体、声光主动调Q基频激光运转,测量了泵浦光斑在激光晶体内的位置变化对输出功率的影响;结果表明,当泵浦光斑位于晶体键合面附近处可以得到最大的输出功率。另外,测量了不同声光调制频率下主动调Q激光的脉冲输出特性。用三维的热传导方程分析了键合晶体内的热透镜焦距和热致折射率损耗随泵浦功率的变化,并与普通的Nd:YVO₄晶体作了比较;用速率方程模型对激光的脉冲特性进行了理论模拟,数值计算结果与实验结果相符。（第四章4.1节）Ⅶ采用三镜折叠腔结构,利用自Q晶体Cr⁴⁺:Nd³⁺:YAG作为饱和吸收体,实现了LD泵浦Nd:YVO₄/YVO₄晶体、被动调Q 1.06μm激光运转,测量了激光输出脉冲宽度、脉冲重复率、单脉冲能量和峰值功率等激光输出特性,并与同样腔型结构下,Cr⁴⁺:YAG被动调Q Nd:YVO₄/YVO₄激光进行了比较。结果表明,用Cr⁴⁺:Nd³⁺:YAG作为饱和吸收体时,激光具有更低的泵浦阈值和更高的光光转换效率。（第四章4.2节）Ⅷ将GaAs同时兼做调Q元件和谐振腔的输出镜,实现了LD泵浦Nd:LuVO₄晶体、GaAs被动调Q 1.06μm激光运转。考虑未镀膜的GaAs形成Fabry-Perot腔,利用吸收系数和透过率的理论计算公式得到了其有效的反射率。在相同的泵浦功率和谐振腔结构的条件下,与Nd:GdVO₄和Cr:Nd:YAG激光晶体相比,Nd:LuVO₄激光可以产生更短的脉冲宽度。另外,还测量了激光平均输出功率、脉冲宽度、脉冲重复率和峰值功率等激光特性。（第四章4.3节）Ⅸ简单的介绍了5mol%MgO掺杂的周期性极化的LiNbO₃（MgO-PPLN）晶体的特性,MgO的掺入可以极大的提高PPLN晶体的抗损伤性能。利用三镜折叠腔实现了LD泵浦Nd:YVO₄/YVO₄晶体、MgO-PPLN内腔倍频、GaAs被动调Q 0.53μm绿激光运转,测量了不同泵浦功率下的脉冲宽度、脉冲重复率、单脉冲能量和峰值功率,分析了准相位匹配PPLN晶体的倍频理论,给出了高斯分布近似下PPLN倍频晶体内二次谐波转换引起的非线性损耗,并利用准相位匹配理论和速率方程模型对实验结果进行了理论模拟。（第五章5.1-5.2节）Ⅹ采用三镜折叠腔结构,实现了LD泵浦Nd:YVO₄/YVO₄晶体、MgO-PPLN腔内倍频、Cr⁴⁺:YAG被动调Q 0.53μm绿激光运转;测量了在不同Cr⁴⁺:YAG小信号透过率、不同泵浦功率下的脉冲宽度、脉冲重复率、单脉冲能量和脉冲峰值功率的变化规律。（第五章5.3节）Ⅺ研究了LD泵浦Nd:YVO₄/YVO₄晶体、AO—GaAs主被动双调Q激光的脉宽控制特性。通过改变GaAs或同时改变AO和GaAs在腔内的位置以及泵浦光束腰在激光介质中的位置,可以有效的改变调Q激光输出脉冲宽度。理论分析中给出了在一定泵浦功率下的平均泵浦半径与泵浦光斑在增益介质内位置的关系,以及腔内任意位置处的传输矩阵和光束半径的计算公式。运用速率方程模型模拟获得了脉宽与振荡光和泵浦光斑大小之间的关系,理论计算与实验结果相符。（第六章6.1节）Ⅻ理论和实验研究了LD泵浦Nd:YVO₄/YVO₄晶体、Cr⁴⁺:YAG和GaAs双被动调Q激光的脉宽控制特性。实验中,通过改变GaAs或同时改变Cr⁴⁺:YAG和GaAs在腔内的位置以及泵浦光束腰在激光介质中的位置,可以有效的控制激光的脉冲宽度。运用平均泵浦半径计算公式、腔内高斯光束半径计算公式以及速率方程模型对实验进行了模拟,理论分析与实验结果相符。（第六章6.2节）本论文中的主要创新工作包括:Ⅰ首次实现了氙灯泵浦Nd:YAG晶体、Cr⁴⁺:YAG—GaAs双被动调Q激光的基频和KTP腔内倍频激光运转,研究了其运转特性;考虑GaAs的单光子、双光子吸收和自由载流子吸收过程,给出了平面波近似下的速率方程模型,数值求解方程的理论计算值与实验结果相符。Ⅱ首次实现了LD泵浦c-cut Nd:GdVO₄晶体、声光—GaAs主被动双调Q 1.06μm和KTP腔内倍频0.53μm激光运转,研究了其运转规律;与a-cut Nd:GdVO₄激光的输出脉冲的宽度、重复率及峰值功率相比,c-cut Nd:GdVO₄激光具有更短的脉宽和更高的峰值功率增长率;用高斯近似下双调Q激光的耦合的速率方程对激光的输出特性进行了模拟,理论计算与实验结果相符。Ⅲ将GaAs同时兼做调Q元件和谐振腔的输出镜,首次实现了LD泵浦Nd:LuVO₄晶体、GaAs被动调Q 1.06μm激光运转,测量了激光平均输出功率、脉冲宽度、脉冲重复率和峰值功率等激光特性。与Nd:GdVO₄和Cr:Nd:YAG激光晶体相比,Nd:LuVO₄激光可以产生更短的脉冲宽度。Ⅳ首次实现了LD泵浦Nd:YVO₄/YVO₄键合晶体、MgO-PPLN准相位匹配内腔倍频、GaAs和Cr⁴⁺:YAG被动调Q 0.53μm绿激光运转,研究了运转特性;利用准相位匹配理论和高斯分布近似下的速率方程模型,对PPLN晶体的倍频特性进行了数值模拟,理论计算和实验结果相符。Ⅴ首次对LD泵浦的Nd:YVO₄/YVO₄晶体、声光—GaAs主被动双调Q及Cr⁴⁺:YAG—GaAs双被动调Q激光的脉宽控制特性进行了研究;通过改变泵浦光斑在增益介质内的位置即改变平均泵浦半径的大小,以及调Q开关在腔内的位置即改变调Q开关处光束半径的大小,能够有效地控制调Q激光的脉冲宽度。运用速率方程模型获得了脉冲宽度与增益介质内平均泵浦半径以及调Q开关处光束半径的关系,从理论上模拟了双调Q脉冲宽度变化的规律,理论计算与实验结果相符。更多还原

【Abstract】 All-solid-state short pulse lasers have wide applications in the fields such as laser telecommunication,remote sensing,information processing,laser processing,medical,and military,due to its advantages such as its simplicity,high efficiency,high stability,long longevity,good beam quality and has been paid much attention on.In this dissertation,by using xenon flash lamp or fiber-coupled laser-diode as the pump source,Nd:YAG,Nd:YVO₄,Nd:GdVO₄ and Nd:LuVO₄ crystals as the gain mediums,we have studied the performance of the diode-pumped doubly Q-switched lasers with AO-GaAs or Cr⁴⁺:YAG-GaAs,the frequency doubling performance of the KTP crystal and MgO doped periodically poled LiNbO₃（PPLN） crystal,as well as the pulse width control of doubly Q-switched lasers with AO-GaAs or Cr⁴⁺:YAG-GaAs.Meanwhile,the coupling rate equations under plane-wave or Gaussian distribution approximation have been established to theoretically analyze the properties of the above-mentioned Q-switched and doubly Q-switched lasers.The main content of this dissertation includes:ⅠUsing xenon flash lamp as pumping source,the doubly Q-switched Nd:YAG laser at 1.06μm with Cr⁴⁺:YAG and GaAs saturable absorbers has been realized.We also compared the laser performances of the doubly Q-switched laser with those of singly Q-switched lasers when there is only a single pulse during one pump pulse.The pulse widths and pulse symmetry factor of the three lasers versus the small signal transmission of Cr⁴⁺:YAG or the output coupler reflectivity have been given.The results show that the doubly passively Q-switched laser can improve the pulse symmetry and narrow the pulse width in comparison with the singly passively Q-switched laser.Considering the single-photon,two-photon and free carriers absorptions of GaAs,the coupling rate equations under the plane-wave approximation have been used to simulate the laser performances,the experimental results are consistent with the theoretical results.（Chapter 2-2.1）ⅡThe research on the laser performance of xenon flash lamp pumped KTP intracavity frequency-doubling Nd:YAG green laser with Cr⁴⁺:YAG and GaAs saturable absorbers have been presented.We have measured the pulse widths and symmetry factor versus small signal transmission of Cr⁴⁺:YAG for both the single passively and the doubly passively Q-switched intracavity-frequency-doubling green lasers when there is only a single pulse on the oscilloscope during one pump pulse.In addition,the dependence of pulse width,average output energy,pulse repetition,single pulse energy and peak power on incident pump energy for different Cr4+:YAG have been measured.We used the coupled rate equation under the plane-wave approximation to simulate the laser performances.The numerical solutions of the rate equations are in agreement with the experimental results.（Chapter 2-2.2）ⅢUsing both acoustic-optic（AO） modulator and GaAs saturable absorber in the same cavity,a diode-pumped doubly Q-switched c-cut Nd:GdVO₄ laser has been realized.We made a comparison between c-cut and a-cut Nd:GdVO₄ crystals and the experimental results shows that the doubly Q-switched c-cut Nd:GdVO₄ laser can generate narrower pulse with higher peak power when the incident pump power higher than 3.4 W.Furthermore,c-cut Nd:GdVO₄ laser can generate the more symmetric pulse with shorter pulse width in comparison with singly AO or GaAs Q-switched laser.Considering the turn-off time of AO Q-switch,the spatial distributions of the intracavity photon density and the population-inversion density,the population-inversion density and pump light,coupled rate equations are introduced to theoretically analyze the experimental results,and the experimental results are in fair agreement with the numerical solutions.（Chapter3-3.1）ⅣThe theoretical and experimental studies on laser diode-pumped doubly Q-switched Nd:GdVO₄/KTP green lasers at 0.53μm have been presented.The rise time and fall time of the pulse,pulse widths,pulse energy and peak power have been measured under different pump power and repetition rates for the doubly and singly Q-switched lasers.Moreover,the comparison between a-cut Nd:GdVO₄/KTP green laser and c-cut Nd:GdVO₄/KTP green laser have been given.Considering the nonlinear loss due to the intracavity second harmonic conversion under Gaussian distribution approximation as well as the thermally induced diffraction loss and the variations of the beam radius at different positions along the cavity axis,coupled rate equations describing the doubly Q-switched intracavity frequency doubling green lasers are given.The theoretical results are consisting with experimental results. （Chapter 3-3.2）ⅤUsing three-mirror-folded cavity,diode-pumped doubly passively Q-switched KTP intracavity frequency-doubling Nd:YVO₄ laser at 0.53μm with Cr⁴⁺:YAG and GaAs saturable absorbers have been realized.For three Cr⁴⁺:YAG wafers with different small signal transmission,the average output power,pulse widths,repetition rates,pulse energy,and peak powers of the doubly Q-switched laser under different pump power have been measured, respectively.In comparison with singly Q-switched laser,doubly Q-switched laser can compress the pulse width,improve the pulse symmetry and improve the pulse energy and peak power.（Chapter 3-3.3）ⅥThe method of manufacturing Nd:YVO₄/YVO₄,as well as its properties,has been presented.A diode-pumped actively Q-switched Nd:YVO₄/YVO₄ laser with AO has been carried out.The experimental studies on the output power versus the location of pumping facula in the laser crystal have been presented.The experimental results show that the maximum laser output power can be obtained when the pumping spot lies in the diffusion-bonded interface of the Nd:YVO₄/YVO₄ crystal.The three dimensional Possion equation has been used to analyze the steady state temperature profile in the laser crystal,and the thermal focus length of the Nd:YVO₄/YVO₄ composite crystal and thermal loss at different pump power are obtained.From the experimental results,we can see that the diffusion bonding crystal can reduce the thermal effect influence of laser crystal.Meanwhile, a rate-equation model for the actively Q-switched laser is used to simulate the laser performance.The numerical solutions are in agreement with the experimental results. （Chapter 4-4.1）ⅦBy using a piece of co-doped Nd³⁺:Cr⁴⁺:YAG crystal as saturable absorber,a laser-diode pumped passively Q-switched Nd:YVO₄/YVO₄ laser has been realized.The maximum laser output power of 2.452W has been obtained at the incident pump power of 8.9W for 8.8%transmission of output coupler at 1064 nm,corresponding to a slope efficiency of 30%.The other output laser characteristics of the laser have also been investigated.The laser with Nd³⁺:Cr⁴⁺:YAG saturable absorber has the lower threshold pump power and the higher slope efficiency compared with the laser with Cr⁴⁺:YAG saturable absorber that with the similar small-signal transmission.The dependence of the pulse width,pulse repetition, pulse energy and peak power on the pump power have also been measured.（Chapter 4-4.2）ⅧBy using GaAs as both a saturable absorber and an output coupler,a laser-diode pumped passively Q-switched Nd:LuVO₄ laser has been realized for the first time to our knowledge.The uncoated GaAs forms a Fabry-Perot cavity,and the effective reflection, absorption and transmission coefficient of the GaAs wafer have been given.The characteristics of the laser such as the average output power,the pulse width,the pulse repetition rate and the peak power have been measured at different incident pump power. Compared with Nd:GdVO₄ and Cr:Nd:YAG laser crystals,much shorter pulse widths can be obtained with the use of a Nd:LuVO₄ laser crystal under a similar pump power level and laser cavity length.（Chapter 4-4.3）ⅨThe properties of the 5mol%MgO doped periodically poled LiNbO₃（MgO-PPLN） have been demonstrated.By adding 5mol%MgO dopant impurities,the optical damage threshold as well as nonlinear coefficients of PPLN crystal is highly increased compared with that of non-doped PPLN crystal.Using the 5mol%MgO doped PPLN as the nonlinear crystal, diode-pumped cw and GaAs passively Q-switched Nd:YVO₄/YVO₄ green laser have been realized.The nonlinear loss due to the second harmonic wave conversion is obtained.In addition,a frequency doubling theory for quasi-phase-matched crystal PPLN are given under Gaussian distribution approximation.The coupled rate equations have been used to simulate the laser,and the theoretical analysis is consistent with the experimental results.（Chapter 5-5.1,5.2）ⅩA diode-pumped MgO-PPLN intracavity frequency doubling Cr⁴⁺:YAG passively Q-switched Nd:YVO₄/YVO₄ green laser has been realized in a three-mirror-folded cavity. Using two pieces of Cr⁴⁺:YAG with different small signal transmission as saturable absorber respectively,the pulse width,pulse repetition,pulse energy,and peak power of the green laser have been measured.（Chapter 5-5.3）ⅪThe methods to control the pulse width of a laser-diode end-pumped doubly Q-switched Nd:YVO₄/YVO₄ composite crystal laser with acoustic-optic（AO） and GaAs saturable absorber has been theoretically and experimentally studied.By varying one or two Q-switchers in the laser cavity and the pumping facula in the gain medium,we provide two kinds of efficient means to control the pulse duration.The average pumping radius versus the location of pumping facula in the laser crystal,as well as the transfer matrix and formula for calculating the beam radius of arbitrary position in the cavity,have been presented.The coupled rate equations are used to analyze the process of the laser.The experimental results are consistent with the theoretical results.（Chapter 6-6.1）ⅫWe have theoretically and experimentally studied the methods to control the pulse duration of a diode-pumped doubly passively Q-switched Nd:YVO₄/YVO₄ composite crystal laser with Cr⁴⁺:YAG and GaAs saturable absorbers.By varying the position of saturable absorbers in the laser cavity or the pumping facula in the gain medium,we can vary the pulse duration of the laser pulse.The coupled rate equations are introduced to simulate the process of the laser,and the theoretical calculation results agree with the experimental results.The main innovations of this dissertation are as follows:ⅠUsing xenon flash lamp as pumping source,we first demonstrated the Cr⁴⁺:YAG-GaAs doubly Q-switched Nd:YAG 1.06μm laser and KTP intracavity frequency-doubling 0.53μm green laser.The pulse widths and pulse symmetry factor of the three lasers versus the small signal transmission of Cr⁴⁺:YAG or the output coupler reflectivity have been given.The results show that the doubly passively Q-switched laser can improve the pulse symmetry and narrow the pulse width in comparison with the singly passively Q-switched laser.Considering the single-photon,two-photon and free carriers absorptions of GaAs,the coupling rate equations under the plane-wave approximation have been used to simulate the laser performances.ⅡUsing both acoustic-optic（AO） modulator and GaAs saturable absorber in the same cavity,diode-pumped doubly Q-switched c-cut Nd:GdVO₄ 1.06μm laser and KTP intracavity frequency-doubling 0.53μm green laser has been first demonstrated.In comparison with a-cut Nd:GdVO₄ laser,c-cut Nd:GdVO₄ laser can generate narrower pulse width and higher peak power when the incident pump power higher than 3.4W and 4.4W for 1.06μm laser and 0.53μm green laser,respectively.Considering the turn-off time of AO Q-switch,the spatial distributions of the intracavity photon density and the population-inversion density,the population-inversion density and pump light,coupled rate equations are introduced to theoretically analyze the experimental results,and the experimental results are in fair agreement with the numerical solutions.ⅢBy using GaAs as both a saturable absorber and an output coupler,a laser-diode pumped passively Q-switched Nd:LuVO₄ laser has been realized for the first time to our knowledge.The characteristics of the lasers such as the average output power,the pulse width, the pulse repetition rate and the peak power have been measured at different incident pump power.Compared with Nd:GdVO₄ and Cr:Nd:YAG laser crystals,much shorter pulse widths can be obtained with the use of a Nd:LuVO4 laser crystal under a similar pump power level and laser cavity length. ⅣUsing the 5mol%MgO doped PPLN as the nonlinear crystal,diode-pumped GaAs and Cr⁴⁺:YAG passively Q-switched Nd:YVO₄/YVO₄ green laser have been first presented. By adding 5mol%MgO dopant impurities,the optical damage threshold as well as nonlinear coefficients of PPLN crystal is highly increased compared with that of non-doped PPLN crystal.By considering the second harmonic conversion as a nonlinear loss of the fundamental wave,we used a rate-equation model considering the quasi-phase-matching theory to simulate the laser performance,and the numerical solution are consistent with the experimental ones.ⅤThe methods to control the pulse width for laser-diode end-pumped AO-GaAs and Cr⁴⁺:YAG-GaAs doubly Q-switched Nd:YVO₄/YVO₄ composite crystal laser has been theoretically and experimentally studied.By varying one or two Q-switchers in the laser cavity and the pumping facula in the gain medium,we provide two kinds of efficient means to control the pulse duration.The average pumping radius versus the location of pumping facula in the laser crystal,as well as the transfer matrix and formula for calculating the beam radius in intracavity arbitrary position,have been presented.The coupled rate equations are used to analyze the process of the laser.The experimental results are consistent with the theoretical results.更多还原