【作者】 李欣；

【导师】 李桂秋；

【作者基本信息】 山东大学 ， 光学工程， 2012， 博士

【摘要】 二极管泵浦的固体激光器具有转换效率高、可靠性好、噪声特性好、频率稳定、结构简单、小型化等优点,被广泛地应用于工业切割和焊接、激光测距、激光制导以及外科手术等各个方面。1.3μm波长的激光在光纤通讯、激光医学、激光微机械加工、人眼安全等领域都有重要应用。本论文采用光纤耦合输出的激光二极管作为泵浦源器件,研究了掺钕的钒酸盐固态晶体(Nd:GdVO4、Nd:GdYVO4系列、Nd:LuYVO4和Nd:GdLuYVO4)的1.3μm连续、调Q以及锁模激光特性。使用的主动调制元件为声光(AO)开关,被动调制元件为V:YAG、Co:LMA、SWCNT饱和吸收体。首先研究了使用V:YAG的Nd:GdVO4晶体基频和倍频被动调Q激光特性,理论模拟了实验结果；实现了Nd:GdYVO4一系列混合晶体的1.3μm连续激光运转,实验测量了相关参数,并使用V:YAG研究和对比了不同掺杂组分晶体的1.3μm基频和671nm倍频调Q激光特性；采用二极管泵浦Nd:LuYVO4两掺混合晶体和Nd:GdLuYVO4三掺混合晶体实现了连续激光输出并测量了热效应,研究了这两种晶体的V:YAG被动调Q性能；研究了Nd:LuYVO4晶体使用V:YAG、Co:LMA和SWCNT饱和吸收体作为调制元件时的被动调Q锁模特性,以及使用AO开关时的主动调Q锁模特性；利用V:YAG、Co:LMA. SWCNT和AO开关结合,研究了Nd:LuYVO4晶体的主被动双调Q锁模输出特性。本论文的具体研究内容为：Ⅰ研究了LD泵浦的Nd:GdVO4晶体在1.3μm波段处的激光特性。通过使用曲率半径不同的输入镜和透过率不同的输出镜来研究其对于连续激光输出的影响。在平凹腔内插入不同小信号透过率的V:YAG饱和吸收体来对Nd:GdVO4晶体的被动调Q脉冲输出进行研究,记录随泵浦功率变化下的脉冲宽度、重复率、单脉冲能量和峰值功率。对实验中出现的重复率的变化现象进行了理论分析,结果表明晶体的热透镜焦距对腔中光束半径有影响,进而削弱了输出性能。使用考虑了泵浦光高斯分布以及腔内光子数密度和反转粒子数密度高斯分布的速率方程组对Nd:GdVO4被动调Q激光器的运转过程进行了理论模拟。Ⅱ使用Ⅴ型三镜折叠谐振腔结构,进行了Nd:GdVO4/KTP腔内倍频红光特性研究。采用Ⅱ类相位匹配的KTP倍频晶体实现了对Nd:GdVO4晶体1.3μm激光的腔内倍频,产生了671nm红光输出,使用V:YAG饱和吸收体获得了脉冲激光输出,研究了输出脉冲激光参数随泵浦功率变化的趋势。实验表明采用此种方法可以有效获得红光输出,激光特性较稳定。使用了同时将腔内光子数密度、激活介质的反转粒子数密度、饱和吸收体基态粒子数密度和泵浦光横向空间等的分布特征考虑进去的速率方程组来进行数值求解,理论模拟实验结果。Ⅲ通过二极管泵浦Nd:GdxY1-xVO4(x=0.19,0.3,0.63,0.83)系列晶体,采用平凹腔,实现了此类晶体的连续激光输出,实验研究了晶体的被动损耗和受激发射截面、热焦距和光束半径随泵浦功率的变化规律。实验表明由于受激发射截面较小,此类晶体的连续输出激光功率不如单晶的大。使用V:YAG做调Q元件实现了混合晶体的被动调Q激光输出,研究了输出性能及与掺杂组分的关系。实验表明,Nd:GdxY1-xVO4混合晶体可以获得性能良好的脉冲激光稳定输出,并且在脉宽、单脉冲能量和峰值功率方面相比单晶有一定提升。Ⅳ选用Nd:GdxY1-xVO4系列混合晶体作为激光材料,利用V型折叠腔和KTP倍频晶体,有效地实现了混合晶体的671nm腔内倍频V:YAG被动调Q红光输出,研究了输出特性随泵浦功率的变化趋势,对比了不同组分的Nd:GdxY1-xVO4晶体的平均激光输出功率、脉冲宽度、重复率以及单脉冲能量和峰值功率。证明此类晶体是获得红光的适宜的激光材料。V实现了二极管泵浦Nd:Lu0.15Y0.85VO4晶体的1.3μm激光输出。采用简单的平凹腔构造研究了不同输出镜透过率下连续激光的输出特性,实验测定了晶体的热效应,计算出激光运转过程中光束半径随泵浦的变化关系,证明了热效应是影响激光输出的因素之一。使用V:YAG实现了Nd:Lu0.15Y0.85VO4晶体的被动调Q运转,对比了不同小信号透过率下的输出特性。研究表明,Nd:Lu0.15Y0.85VO4晶体可以作为获得1.3μm脉冲激光的优良介质。Ⅵ实现了Nd:GdLuYVO4晶体的1.3μm连续激光输出。选用不同透过率的输出镜组成平凹谐振腔,对比了Nd:GdLuYVO4晶体1.3μm连续输出特性,实验测定了晶体的被动损耗、受激发射截面和热效应。研究表明,Nd:GdLuYVO4晶体的热透镜焦距较小在泵浦较大时热效应明显,影响了激光的输出。使用V:YAG被动饱和吸收体来实现Nd:GdLuYVO4晶体的被动调Q脉冲激光输出,测量了激光的输出特性,对比了Nd:GdLuYVO4晶体与其他晶体的输出参数。Ⅶ采用V型折叠腔结构,使用二极管泵浦Nd:Lu0.15Y0.85VO4晶体,实现了1.3μm波段激光的调Q锁模运转。首先使用不同透过率的输出镜,研究V型腔连续激光的输出特性,证明使用此种腔型结构可以有效地输出1.3μm激光。然后将V:YAG、Co:LMA. SWCNT被动饱和吸收体放入腔中靠近输出镜的位置,实现了Nd:Lu0.15Y0.85VO4混合晶体的被动调Q锁模激光运转,测量了输出功率、调Q脉宽、调Q单脉冲能量以及锁模脉宽和重复率。获得了锁模深度90%左右,锁模脉宽在皮秒量级的短脉冲激光输出。Ⅷ在Z型折叠腔结构中,用二极管泵浦Nd:Lu0.15Y0.85VO4晶体,使用1.3μm波段的声光开关实现了主动调Q锁模运转,研究了不同声光重复率下的输出特性。分别记录了输出功率、调Q脉宽、调Q单脉冲能量以及锁模脉宽和重复率随泵浦光强度的变化规律,探讨了声光开关对于激光锁模运转的调制效果,获得了能量较大的短脉冲激光输出。Ⅸ实现了Nd:Lu0.15Y0.85VO4晶体1.3μm激光波段的V:YAG/AO主被动双调Q锁模运转。通过采用Z型折叠腔,在靠近晶体的位置放置AO开关,在靠近输出镜的位置放置V:YAG,增大泵浦功率获得了锁模脉冲激光输出,记录了输出脉宽、单脉冲能量等参数。相比单V:YAG被动调Q锁模,主被动调Q锁模运转的脉宽被压缩,能量有提升,脉冲对称性更加优良。实验结果说明采用V:YAG/AO主被动双调制的方式可以改善脉冲激光的输出性能。X采用同时使用Co:LMA饱和吸收体和AO开关的方式,通过V型折叠腔,实现了Nd:Lu0.15Y0.85VO4晶体双调Q锁模激光运转,获得了稳定的短脉冲激光输出。实验表明,单Co:LMA被动调Q锁模的输出特性在加入AO开关之后被显著地提升,脉冲能量提高了九倍,脉冲宽度压缩到百分之二十,调Q波形的对称性有了很大提高。采用Co:LMA/AO的主被动双调Q锁模可以有效增大脉冲能量,提高输出光束质量。Ⅺ采用V型腔,使用SWCNT新型饱和吸收体和AO开关相结合作为调制元件,对Nd:Lu0.15Y0.85VO4晶体的调Q锁模特性进行提高。研究表明,通过加入AO,锁模激光脉冲能量有显著提高,脉冲宽度被进一步压缩,锁模深度有所提高,脉冲序列串的振幅波动性明显降低。实验结果说明采用SWCNT/AO主被动相结合的双调Q锁模的方式可以获得稳定性更好、脉宽更窄、能量更大的激光输出。本论文的创新工作主要包含：Ⅰ首次对Nd:GdxY1-xVO4(x=0.19,0.3,0.63,0.83)系列混合晶体在1.3μm波段的激光表现进行了对比。实现了连续激光输出,实验研究了晶体的被动损耗和受激发射截面、热焦距和光束半径随泵浦功率的变化规律。使用V:YAG做调Q元件对比了此类晶体的被动调Q激光特性。利用V:YAG和KTP倍频晶体,实现了混合晶体的腔内倍频红光671nm被动调Q输出,对比了不同组分的Nd:GdxY1-xVO4晶体的平均激光输出功率、脉冲宽度、重复率以及单脉冲能量和峰值功率。证明了混合晶体的激光特性比传统单晶要优秀,更适宜做脉冲激光的增益介质。Ⅱ首次实现了Nd:Lu0.15Y0.85VO4晶体1.3μm激光连续和被动调Q运转。实验测定了晶体的热效应,分析了其对输出性能的影响,计算出激光运转过程中光束半径随泵浦的变化关系。使用V:YAG实现了Nd:Lu0.15Y0.85VO4晶体被动调Q运转,对比了不同小信号透过率情况下的输出特性。证实了Nd:Lu0.15Y0.85VO4晶体可以有效地产生1.3μm激光,被动调Q性能良好,可以获得性能稳定的短脉冲,是作为调Q激光器激光材料的合适选择。Ⅲ首次实现了LD泵浦Nd:GdLuYVO4三掺混合晶体1.3μm激光输出。研究了不同输出透过率情况下的激光性能,获得了稳定的输出。实验测定了晶体的被动损耗、受激发射截面和热效应,说明了其对输出性能的影响。使用V:YAG饱和吸收体实现了Nd:GdLuYVO4晶体的被动调Q脉冲激光输出,测量了激光的脉宽、单脉冲能量和峰值功率,与其他单晶和两掺混合晶体进行了输出特性的对比。Ⅳ首次对Nd:Lu0.15Y0.85VO4晶体1.3μm的调Q锁模激光特性进行研究。采用V型或Z型折叠腔,使用被动饱和吸收体V:YAG、Co:LMA、SWCNT以及AO开关,分别实现了Nd:Lu0.15Y0.85VO4晶体的被动和主动调Q锁模运转,测量了输出功率、调Q脉宽、调Q单脉冲能量以及锁模脉宽和重复率。证实采用这几种调制方式都可以有效地产生调Q锁模激光输出,获得脉宽皮秒量级的锁模短脉冲,特性比较稳定。Ⅴ首次采用被动调制与主动调制结合的方式实现了Nd:Lu0.15Y0.85VO4晶体1.3μm激光的双调Q锁模运转。采用V:YAG/AO、Co:LMA/AO、SWCNT/AO三种主被动双调制的方式,实现了Nd:Lu0.15Yo.85VO4晶体的双调Q锁模激光输出,记录了它们的输出脉宽、单脉冲能量,并与单V:YAG、单Co:LMA、单SWCNT被动调Q锁模的特性进行了对比,获得了比单被动调Q锁模脉宽更窄、能量更大、脉冲更稳定的激光输出。更多还原

【Abstract】 Laser-diode-pumped solid-state laser has the advantages of high conversion efficiency, good reliability and noise characteristics, frequency stability, simple structure and miniaturization. So it has been widely applied in the fields of industrial cutting and welding, laser ranging, laser guidance, surgery and so on. The lasers at1.3μm have important applications in fiber-optic communications, laser medicine, laser micromachining, eye-safe regions. In this dissertation, by using the fiber-coupled laser-diode as the pump source, we have studied the continuous-wave (CW), passively Q-switched and mode-locked1.3-μm laser performances of Nd3+-doped vanadate crystals (Nd:GdVO4, Nd:GdYVO4,Nd:LuYVO4and Nd:GdLuYVO4). In the experiments, acoustic-optic (AO) is employed as the active Q-switch component, V:YAG, Co:LMA and SWCNT saturable absorbers are employed as the passive Q-switch components. We have studied the Q-switched characteristics of fundamental frequency and frequency doubling lasers with Nd:GdVO4/V:YAG, and theoretically simulated the experimental results. The CW laser operations for a class of mixed Nd:GdYVO4crystals have been realized, and the relevant parameters have been experimentally measured. Meanwhile the Q-switched characteristics of fundamental frequency and frequency doubling lasers with V:YAG for different Nd:GdYVO4crystals have been compared. LD-pumped Nd:LuYVO4and Nd:GdLuYVO4CW lasers have been studied, thermal effects have been measured, and the researches on passively Q-switched performances have also been done. By using Nd:LuYVO4, we have done the researches on the output characteristics of passively Q-switched mode-locked lasers with V:YAG, Co:LMA, SWCNT and actively Q-switched mode-locked laser with AO. At last, we have simultaneously employed V:YAG, Co:LMA, or SWCNT with AO in cavities of LD-pumped Nd:LuYVO4laser to study the performances of hybrid mode-locked laser operations.The specific research contents of this dissertation include:(Ⅰ) The research on LD-pumped Nd:GdVO41.3-μm laser has been done. We have used input mirrors with different curvature radii and output mirrors with different transmissions to compare the CW laser output characteristics. By inserting V:YAGs with different initial transmissions into the plano-concave cavity, the passively Q-switched operation is carried out. The variations of pulse width, repetition rate, single pulse energy and peak power versus pump power have been measured. The theoretical analysis on the variation of repetition rate has been done. The experimental results have shown that the thermal focal length can affect the beam radii and weaken the output characteristics. By considering the Gaussian distributions of pump beam, intracavity photon density and population-inversion density into the rate equations, we have simulated the experimental results.(Ⅱ) The Nd:GdVO4/KTP intracavity frequency doubling red laser has been demonstrated in a V-shape cavity. KTP with type-Ⅱ phase matching has been employed to realize the intracavity frequency doubling laser operation, and V:YAG has been employed to obtain pulse laser outputs. Along the pump power increasing, the output characteristics have been measured. The experiments have shown that, with Nd:GdVO4/KTP, the system can generate stable red laser pulses. The rate equations that simultaneously consider the Gaussian distributions of the pump beam, the intracavity photon and the population-inversion densities, have been solved to simulate the experimental results.(Ⅲ) By LD pumping a class of mixed Nd:GdxY1-VO4(x=0.19,0.3,0.63,0.83) crystals, we have presented the1.3-μm CW lasers in plano-concave cavities. The passive losses, stimulated emission cross-sections and thermal focal lengths as well as variations of beam radii have been experimentally measured. The CW output powers for Nd:GdxY1-xVO4crystals are poor due to the relatively small stimulated emission cross-sections. The passively Q-switched operations have been carried out with V:YAG saturable absorber, and the variations of output characteristics versus Gd-doped proportion have been demonstrated. As been shown, the Nd:GdxY1-xVO4mixed crystals can generate stable laser pulses with shorter pulse widths, larger energies and higher peak powers than Nd:GdVO4.(Ⅳ) The performances of passively Q-switched intracavity frequency-doubling Nd:GdxY1-xVO4red lasers in V-shape cavity with KTP and V:YAG have been demonstrated. We have measured the output characteristics, including the average output powers, pulse widths, single pulse energies and peak powers, and testified that Nd:GdxY1-xVO4are suitable laser crystals for red lasers. (Ⅴ) The output of1.3-μm laser with LD-pumped Nd:Lu0.15Yo.ssVO4crystal has been realized. We record the CW output powers with simple plano-concave cavity and different output transmissions, experimentally measure the thermal effects, calculate the variations of beam radii versus pump power during the laser operation and finally confirm that the thermal effect weakens the output characteristics. In addition, V:YAG is used to realize the passively Q-switched laser operation and the output performances with different V:YAG initial transmissions are compared. The research shows that Nd:Lu0.15Y0.85VO4crystal can be a good medium to generate1.3-μm pulse lasers.(Ⅵ) We have demonstrated the output of1.3-μm laser with Nd:GdLuYVO4crystal. Under different output transmissions, the CW laser output performance has been compared. The influences of the passive loss, stimulated emission cross-section and thermal effect on the laser characteristics have been experimentally demonstrated. The relatively small thermal focal length deduces serious thermal effect and weakens the laser output performance. The passively Q-switched operation with V:YAG has been carried out and the laser pulse property has been depicted and compared.(Ⅶ) It is viable to use Ⅴ-shape cavity and LD pumped source to realize the Q-switched mode-locked laser operation for Nd:Lu0.15Y0.85VO4crystal. At first, the CW laser output characteristics in V-shape cavity under different output transmissions have been displayed. Then V:YAG, Co:LMA and SWCNT saturable absorbers are located near the output mirror to realize the passively Q-switched mode-locked operations. We measure the output powers, Q-switched pulse widths, Q-switched pulse energies and mode-locked widths as well as the repetition rates. The modulation depths can be near90%, and the mode-locked widths are under picosecond order.(Ⅷ) In a Z-shape cavity, we study the actively Q-switched mode-locked performance of Nd:Lu0.15Y0.85VO4laser with AO modulator. Under different AO repetition rates, the variations of the output powers, Q-switched pulse widths, Q-switched pulse energies and mode-locked widths as well as the repetition rates versus pump power have been measured. With AO modulator, the actively Q-switched mode-locked operation of Nd:Lu0.15Y0.85VO4laser can generate short pulse with large energy.(Ⅸ) The V:YAG/AO actively and passively Q-switched mode-locked operation at1.3 um with Nd:Lu0.15Y0.85VO4crystal has been presented. In the Z-shape cavity, the AO modulator is located near the laser crystal, the V:YAG is located near the output mirror, and the characteristics have been recorded as the pump power increasing. In contrast to single passively Q-switched mode-locked, the hybrid Q-switched mode-locked operation owns shorter pulse width, larger pulse energy and better pulse symmetry. So the actively and passively Q-switched mode-locked operation can enhance the laser characteristics.(X) By employing Co:LMA and AO in a V-shape cavity, we obtain stable short laser pulse in doubly Q-switched mode-locked Nd:Lu0.15Y0.85VO4laser. The experimental results show that the laser performance has been distinctly enhanced-the pulse energy is9times, the pulse width is only20%and the symmetry has been improved-after the AO being located into the single passively Q-switched mode-locked cavity. This operation can effectively enhance the pulse energy and the beam quality.(Ⅺ) Using SWCNT and AO in a V-shape cavity is an effective way to improve the Q-switched mode-locked pulse performance. The research has shown that the insertion of the AO modulator has caused the increase of pulse energy and the decrease of pulse width. Moreover, the modulation depth can be90%and the amplitude fluctuation is largely reduced. It is demonstrated that by using SWCNT/AO hybrid Q-switched mode-locked operation, we can obtain laser pulse with better stability, shorter pulse width and larger energy.The main innovations of this dissertation are as follows:(I) We have firstly compared the output laser performances at1.3μm with a class of Nd:GdxY1-xVO4mixed crystals (x=0.19,0.3,0.63,0.83). The CW lasers have been realized at first. We experimentally measure the passive losses, stimulated emission cross-sections and thermal focal lengths as well as variations of beam radii. The passively Q-switched operations have been carried out with V:YAG saturable absorber, and the intracavity frequency-doubling passively Q-switched operations have been realized in V-shape cavity with KTP and V:YAG. The variations of the output characteristics, including average output powers, pulse widths, single pulse energies and peak powers, versus Gd-doped proportion have been demonstrated. As been shown, Nd:GdxY1-xVO4mixed crystals can generate stable pulses with shorter pulse widths, larger energies and higher peak powers than Nd:GdVO4.(II) The CW and passively Q-switched laser operations at1.3μm with Nd:Lu0.15Y0.85VO4crystal have been realized for the first time. We experimentally measure the thermal effect, analysis the influence of thermal effect on output characteristics, and calculate the variations of beam radii versus pump power during the laser operation. V:YAG is used to realize the passively Q-switched laser operation and the output performances with different V:YAG initial transmissions are also compared. The research shows that the Nd:Lu0.15Y0.85VO4crystal can be a good medium to generate1.3-μm lasers and obtain stable pulses.(Ⅲ) We have firstly realized the stable1.3-μm laser output with Nd:GdLuYVO4crystal. The CW laser performances with different output transmissions have been compared. We experimentally measure the influences of passive loss, stimulated emission cross-section and thermal effect on the laser characteristics. With V:YAG, the passively Q-switched operation has been carried out and the laser pulse properties have been depicted and compared.(Ⅳ) We have firstly studied the Q-switched mode-locked operation of Nd:Lu0.15Y0.85VO4crystal. Using V or Z shape cavity, and V:YAG, Co:LMA, SWCNT saturable absorbers or AO modulator, the outputs of the Q-switched mode-locked laser pulses have been realized. The output powers, Q-switched pulse widths, Q-switched pulse energies and mode-locked widths as well as the repetition rates have been measured. It is demonstrated that these types of Q-switched mode-locked operations can generate stable and short pulses with large energies.(Ⅴ) We have firstly realized the doubly Q-switched mode-locked operations of Nd:Lu0.15Y0.85VO4crystal by using active and passive Q-switch components. The V:YAG/AO, Co:LMA/AO and SWCNT/AO hybrid types are employed to obtain doubly Q-switched mode-locked operations. The output characteristics, including the Q-switched pulse widths and single pulse energies, have been recorded and compared with those obtained by single V:YAG, Co:LMA, or SWCNT passively Q-switched mode-locked operations. The hybrid Q-switched mode-locked operations can obtain shorter pulse widths, larger pulse energies and better pulse stabilities.更多还原