半导体泵浦Nd～（3+）：GdVO_4激光中的调Q锁模技术
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摘要
脉冲激光器在激光雷达、通讯、材料加工、非线性频率转换等领域具有广泛的应用，采用半导体激光器泵浦的固体激光器具有转换效率高、工作寿命长、结构简单、性能稳定等诸多优点，所以在半导体激光器泵浦的固体激光器中通过调Q或者锁模的方法实现短脉冲激光输出已经成为激光器发展的新方向。在本论文中，我们讨论了在半导体激光器泵浦的Nd：GdVO_4固体激光器中获得调Q锁模(和连续锁模)脉冲激光输出的几种方法。
作为一种新的激光品体，Nd：GdVO_4具有导热性能好、吸收截面大、发射带宽宽等优点，因此决定了它在同类激光晶体中具有很强的竞争力。在第一章中，我们简述了调Q锁模的理论，介绍了Nd：GdVO_4晶体的特性并且与几种常用的晶体进行了比较。然后在后面的三章中，我们分别讨论了三种在Nd：GdVO_4固体激光器中获得调Q锁模脉冲方法，如下所述：
用可饱和吸收体Cr~(4+)：YAG实现调Q锁模：因为Cr~(4+)：YAG的具有基态饱和吸收(GSA)和激发态饱和吸收(ESA)特性，并且其相应能级的弛豫时间分别在微秒和皮秒量级，我们可以利用Cr~(4+)：YAG的这种特性来构建凋Q锁模的激光器。实验中我们获得了波长在1.06μm、最大输出功率为3.22 W的调Q锁模激光脉冲输出，并且对调Q锁模的调制深度以及其转变为连续锁模可能性进行了讨论。
用半导体可饱和吸收镜(SESAM)调Q锁模：SESAM具有两种不同的时间响应特性，这使得在用SESAM实现锁模的时候也会产生调Q的脉冲包络，可以用SESAM的这种特性来构建调Q锁模的激光器。实验中我们在获得了1.06μm的最大输出功率为3.5W的调Q锁模激光脉冲输出和最大输出功率4.9 W的连续锁模脉冲输出。通过自相关测量测得连续锁模脉冲的宽度为11.5 ps。在这部分内
容里，我们同样对调Q锁模到连续锁模的变化条件进行了讨论。
N矿＼GdVO。晶体的自锁模：我们简单分析了获得自锁模的方法，并且通过
实验在＊矿＼0dVO。激光器中获得自锁模脉冲输出。但足山／＊矿‘离于的上能级
比较长，在产生自锁模的同时比较容易产生闩⑤Q，实验小我们获得了自调Q
自锁模的激光脉冲。我们讨论了抑制自调Q包给的方法，并且在实验中获得了
稳定的连续自锁模脉冲。
Pulsed lasers have been used widely in various fields, such as range finder, optical communication, material process, and nonlinear frequency conversion. Diode-pumped solid-state lasers have various advantages such as high conversion efficiency, long working lifetime, simplicity, and stability. Consequently, developing techniques for Q-switching or mode-locking in diode-pumped lasers has been burgeoning as new exploration to get compact pulsed lasers. In this dissertation, we discuss several techniques to generate Q-switched mode-locked (or stable cw mode-locked) laser pulses in diode-pumped Nd:GdVO4 solid-state lasers.
In chapter 1, we firstly review the history of diode-pumped solid-state lasers and give a brief introduction to the theory of Q-switched mode-locking. Secondly, we present the properties of Nd:GdVO4 crystal and compare it with several commonly used laser crystals. As a new laser material, Nd:GdVO4 crystal has the advantages of high thermal conductivity, large absorption cross-section and wide emission bandwidth and so on, which make the Nd:GdVO4 crystal more competent than some other laser crystals. And in the following three chapters, we demonstrate three techniques to obtain Q-switched mode-locked (or cw mode-locked) lasers pulses in diode-pumped Nd:GdVO4 solid-state lasers.
Q-switched mode-locking with Cr4+: YAG crystals: Cr4+:YAG possesses the properties of ground-state saturable absorption (GSA) and exited-state saturable absorption (ESA). And the relaxation times of GSA and ESA are in the region of microsecond and picosecond, respectively. Those characteristics can be applied to construct Q-switched and mode-locked lasers. In our experiments, we obtained 3.22 W Q-switched and mode-locked laser output in the 1.06 μm. The modulation depth and the probability of obtaining cw mode-locking are also discussed in this part.
Q-switched mode-locking with semiconductor saturable absorber mirrors (SESAMs): SESAMs have two kinds of response times, which usually lead to the Q-switched pulse envelope in the lasers mode-locked by SESAM. Therefore, SESAM can be used to achieve Q-switched mode-locked laser pulses. In the experiments, we obtained 3.5 W Q-switched mode-locked and 4.9 W cw mode-locked laser outputs. The pulse width of the cw mode-locked pulse was measured by a homemade autocorrelator to be 11.5 ps. The condition of transforming from the Q-switched mode-locked to cw mode-locked operation was also discussed in this part.
Self-mode-locking in Nd3+:GdVO4 lasers: we analyzed simply the method to achieve self-mode-locking, and experimentally obtained self-mode-locked pulse train in the Nd3+:GdVO4 laser. Due to the long upper-level life-time of Nd3+ ions, the self-mode-locked pulses tend to concentrated in the self-Q-switched envelope. Therefore, in our experiment, self-Q-switched self-mode-locked laser pulses were achieved. In this part, we discussed methods to suppress the self-Q-switched envelopes and experimentally obtained stable cw self-mode-locked laser pulses.
作为一种新的激光品体，Nd：GdVO_4具有导热性能好、吸收截面大、发射带宽宽等优点，因此决定了它在同类激光晶体中具有很强的竞争力。在第一章中，我们简述了调Q锁模的理论，介绍了Nd：GdVO_4晶体的特性并且与几种常用的晶体进行了比较。然后在后面的三章中，我们分别讨论了三种在Nd：GdVO_4固体激光器中获得调Q锁模脉冲方法，如下所述：
用可饱和吸收体Cr~(4+)：YAG实现调Q锁模：因为Cr~(4+)：YAG的具有基态饱和吸收(GSA)和激发态饱和吸收(ESA)特性，并且其相应能级的弛豫时间分别在微秒和皮秒量级，我们可以利用Cr~(4+)：YAG的这种特性来构建凋Q锁模的激光器。实验中我们获得了波长在1.06μm、最大输出功率为3.22 W的调Q锁模激光脉冲输出，并且对调Q锁模的调制深度以及其转变为连续锁模可能性进行了讨论。
用半导体可饱和吸收镜(SESAM)调Q锁模：SESAM具有两种不同的时间响应特性，这使得在用SESAM实现锁模的时候也会产生调Q的脉冲包络，可以用SESAM的这种特性来构建调Q锁模的激光器。实验中我们在获得了1.06μm的最大输出功率为3.5W的调Q锁模激光脉冲输出和最大输出功率4.9 W的连续锁模脉冲输出。通过自相关测量测得连续锁模脉冲的宽度为11.5 ps。在这部分内
容里，我们同样对调Q锁模到连续锁模的变化条件进行了讨论。
N矿＼GdVO。晶体的自锁模：我们简单分析了获得自锁模的方法，并且通过
实验在＊矿＼0dVO。激光器中获得自锁模脉冲输出。但足山／＊矿‘离于的上能级
比较长，在产生自锁模的同时比较容易产生闩⑤Q，实验小我们获得了自调Q
自锁模的激光脉冲。我们讨论了抑制自调Q包给的方法，并且在实验中获得了
稳定的连续自锁模脉冲。
Pulsed lasers have been used widely in various fields, such as range finder, optical communication, material process, and nonlinear frequency conversion. Diode-pumped solid-state lasers have various advantages such as high conversion efficiency, long working lifetime, simplicity, and stability. Consequently, developing techniques for Q-switching or mode-locking in diode-pumped lasers has been burgeoning as new exploration to get compact pulsed lasers. In this dissertation, we discuss several techniques to generate Q-switched mode-locked (or stable cw mode-locked) laser pulses in diode-pumped Nd:GdVO4 solid-state lasers.
In chapter 1, we firstly review the history of diode-pumped solid-state lasers and give a brief introduction to the theory of Q-switched mode-locking. Secondly, we present the properties of Nd:GdVO4 crystal and compare it with several commonly used laser crystals. As a new laser material, Nd:GdVO4 crystal has the advantages of high thermal conductivity, large absorption cross-section and wide emission bandwidth and so on, which make the Nd:GdVO4 crystal more competent than some other laser crystals. And in the following three chapters, we demonstrate three techniques to obtain Q-switched mode-locked (or cw mode-locked) lasers pulses in diode-pumped Nd:GdVO4 solid-state lasers.
Q-switched mode-locking with Cr4+: YAG crystals: Cr4+:YAG possesses the properties of ground-state saturable absorption (GSA) and exited-state saturable absorption (ESA). And the relaxation times of GSA and ESA are in the region of microsecond and picosecond, respectively. Those characteristics can be applied to construct Q-switched and mode-locked lasers. In our experiments, we obtained 3.22 W Q-switched and mode-locked laser output in the 1.06 μm. The modulation depth and the probability of obtaining cw mode-locking are also discussed in this part.
Q-switched mode-locking with semiconductor saturable absorber mirrors (SESAMs): SESAMs have two kinds of response times, which usually lead to the Q-switched pulse envelope in the lasers mode-locked by SESAM. Therefore, SESAM can be used to achieve Q-switched mode-locked laser pulses. In the experiments, we obtained 3.5 W Q-switched mode-locked and 4.9 W cw mode-locked laser outputs. The pulse width of the cw mode-locked pulse was measured by a homemade autocorrelator to be 11.5 ps. The condition of transforming from the Q-switched mode-locked to cw mode-locked operation was also discussed in this part.
Self-mode-locking in Nd3+:GdVO4 lasers: we analyzed simply the method to achieve self-mode-locking, and experimentally obtained self-mode-locked pulse train in the Nd3+:GdVO4 laser. Due to the long upper-level life-time of Nd3+ ions, the self-mode-locked pulses tend to concentrated in the self-Q-switched envelope. Therefore, in our experiment, self-Q-switched self-mode-locked laser pulses were achieved. In this part, we discussed methods to suppress the self-Q-switched envelopes and experimentally obtained stable cw self-mode-locked laser pulses.
引文
1. B.C. Weber, A. Hirth. "Efficient single-pulse emission with submicrosecond duration from a Cr:LiSAF laser." Opt. Comm. 128, 158(1996).
2. M. C. Marconi, O. E. Martinez, and F. P. Diodati. "Q switching by self-focusing.".Opt. Lett. 10, 402(1985).
3. D. E. Spence, P. N. Kean, and W. Sibbet. "60-fsec pulse generation from a self-mode-locked Ti:sapphire laser." Opt. Lett: 16, 42(1991).
4. H. Liu, J. Nees, and G. Mourou. "Diode-pumped Kerr-lens mode-locked Yb:KY(WO_4)_2 laser."Opt. Lett. 26, 1723(2001).
5. V. Petrov, U. Griebner, D. Ehrt and W. Seeber. "Femtosecond self mode locking of Yb fluoride phosphate glass laser." Opt. Lett. 22, 408(1997).
6. K. A. Stankov. Appl. Phys. B 45, 191(1988).
7. A. A. Mani et al. "All-solid-state 12 ps actively passively mode-locked pulsed Nd: YAG laser using a nonlinear mirror." Appl. Phys. Lett. 75, 3066(1999).
8. K. A. Stankov. "Mode locking by a frequency-doubling crystal: generation of transform-limited ultrashort light pulses." Opt. Lett. 14, 359(1989).
9. U. Keller, T. H. Chiu, J. F. Ferguson. "Self-starting femtosecond mode-locked Nd: glass laser that uses intracavity saturable absorbers." Opt. Lett., 18, 1077.(1993).
10. A.I. Zagumennyi, V.G. Ostroumov, I.A. Shcherbakov, T. Jensen, J.P. Meyen, G. Huber. "Nd:GdVO4 crystal: a new material for diode-pumped lasers." Sov. J. Quantum Electron. 22, 1072(1992).
11．侯印春，周哲仪，颜声辉。《光功能晶体》。中国计量出版社，1991年
12. Huaijin Zhang, Xianlin Meng, Li Zhu, and Zhaohe Yang."Growth and thermal properties of Nd: GdVO_4 Single Crystal." Materials Research Bulletin, 34, 1589,(1999).
13. T. Jensen, V.G.Ostroumov, J.-P.Meyn, G.Huber, A. I. Zagumennyi, I.A.Shcherbakov. "Spectroscopic Characterization and Laser Perfomance of
Diode-Laser-pumped Nd: GdVO_4 "Appl. Phys. B 58, 373. (1994).
14. L. Fornasiero, S.Kück, T. Jensen, G. Huber, B.H.T. Chai. "Excited state absorption and stimulated emission of Nd~(3+) in crystals.", Appl. Phys. B 67, 549(1998).
15. Huaijin Zhang, Xianlin Meng, Junhai Liu, Li Zhu, Changqing Wang, Zongshu Shao, Jiyang Wang, Yaogang Liu. "Growth of lowly Nd doped GdVO_4 single crystal and its laser properties." Journal of Crystal Growth 216, 367(2000).
16. T. Ogawa, Y. Urata, S. Wada, K. Onodera, H. Machida, H. Sagae, M. Higuchi, and K. Kodaira,"Efficient laser performance of Nd: GdVO_4 crystals grown by the floating zone method" Opt. Lett. 28, 2333(2003).
17. V. Lupei, N. Pavel, Y. Sato and T. Taira. "Highly efficient 1063-nm continuous-wave laser emission in Nd: GdVO_4" Opt. Lett. 28, 2366, (2003).
18．W．克西耐尔著，孙文，江泽文，程国祥译“Solid-state Laser Engineering”科学出版社，2002。
19. Guiwu Lu, Chunxi Li, Wenchuan Wang, Zihao Wang, Hairui Xia, Peng Zhao。"Raman investigation of lattice vibration modes and thermal conductivity of Nd-doped zircon-type laser crystals." Materials Science and Engineering B 98, 156, (2003).
20. L. J. Qin, X. L. Meng, H. Y. Shen, L. Zhu, B. C. Xu, L. X. Huang, H. R. Xia, P. Zhao, G. Zheng. "Thermal conductivity and refractive indices of Nd: GdVO_4. crystals" Cryst. Res. Technol. 38, 793(2003).
21. P. A. Studennikin, A.I. Zagumennyi, Y.D. Zavartsev, P.A. Popov, and I.A. Shcherbakov, "GdVO_4 as a new medium for solid-state lasers: some optical and thermal properties of crystals doped with Nd~(3+), Tm~(3+), and Er~(3+)ions," Quantum Electron., 25, 1162, (1995).
2. M. C. Marconi, O. E. Martinez, and F. P. Diodati. "Q switching by self-focusing.".Opt. Lett. 10, 402(1985).
3. D. E. Spence, P. N. Kean, and W. Sibbet. "60-fsec pulse generation from a self-mode-locked Ti:sapphire laser." Opt. Lett: 16, 42(1991).
4. H. Liu, J. Nees, and G. Mourou. "Diode-pumped Kerr-lens mode-locked Yb:KY(WO_4)_2 laser."Opt. Lett. 26, 1723(2001).
5. V. Petrov, U. Griebner, D. Ehrt and W. Seeber. "Femtosecond self mode locking of Yb fluoride phosphate glass laser." Opt. Lett. 22, 408(1997).
6. K. A. Stankov. Appl. Phys. B 45, 191(1988).
7. A. A. Mani et al. "All-solid-state 12 ps actively passively mode-locked pulsed Nd: YAG laser using a nonlinear mirror." Appl. Phys. Lett. 75, 3066(1999).
8. K. A. Stankov. "Mode locking by a frequency-doubling crystal: generation of transform-limited ultrashort light pulses." Opt. Lett. 14, 359(1989).
9. U. Keller, T. H. Chiu, J. F. Ferguson. "Self-starting femtosecond mode-locked Nd: glass laser that uses intracavity saturable absorbers." Opt. Lett., 18, 1077.(1993).
10. A.I. Zagumennyi, V.G. Ostroumov, I.A. Shcherbakov, T. Jensen, J.P. Meyen, G. Huber. "Nd:GdVO4 crystal: a new material for diode-pumped lasers." Sov. J. Quantum Electron. 22, 1072(1992).
11．侯印春，周哲仪，颜声辉。《光功能晶体》。中国计量出版社，1991年
12. Huaijin Zhang, Xianlin Meng, Li Zhu, and Zhaohe Yang."Growth and thermal properties of Nd: GdVO_4 Single Crystal." Materials Research Bulletin, 34, 1589,(1999).
13. T. Jensen, V.G.Ostroumov, J.-P.Meyn, G.Huber, A. I. Zagumennyi, I.A.Shcherbakov. "Spectroscopic Characterization and Laser Perfomance of
Diode-Laser-pumped Nd: GdVO_4 "Appl. Phys. B 58, 373. (1994).
14. L. Fornasiero, S.Kück, T. Jensen, G. Huber, B.H.T. Chai. "Excited state absorption and stimulated emission of Nd~(3+) in crystals.", Appl. Phys. B 67, 549(1998).
15. Huaijin Zhang, Xianlin Meng, Junhai Liu, Li Zhu, Changqing Wang, Zongshu Shao, Jiyang Wang, Yaogang Liu. "Growth of lowly Nd doped GdVO_4 single crystal and its laser properties." Journal of Crystal Growth 216, 367(2000).
16. T. Ogawa, Y. Urata, S. Wada, K. Onodera, H. Machida, H. Sagae, M. Higuchi, and K. Kodaira,"Efficient laser performance of Nd: GdVO_4 crystals grown by the floating zone method" Opt. Lett. 28, 2333(2003).
17. V. Lupei, N. Pavel, Y. Sato and T. Taira. "Highly efficient 1063-nm continuous-wave laser emission in Nd: GdVO_4" Opt. Lett. 28, 2366, (2003).
18．W．克西耐尔著，孙文，江泽文，程国祥译“Solid-state Laser Engineering”科学出版社，2002。
19. Guiwu Lu, Chunxi Li, Wenchuan Wang, Zihao Wang, Hairui Xia, Peng Zhao。"Raman investigation of lattice vibration modes and thermal conductivity of Nd-doped zircon-type laser crystals." Materials Science and Engineering B 98, 156, (2003).
20. L. J. Qin, X. L. Meng, H. Y. Shen, L. Zhu, B. C. Xu, L. X. Huang, H. R. Xia, P. Zhao, G. Zheng. "Thermal conductivity and refractive indices of Nd: GdVO_4. crystals" Cryst. Res. Technol. 38, 793(2003).
21. P. A. Studennikin, A.I. Zagumennyi, Y.D. Zavartsev, P.A. Popov, and I.A. Shcherbakov, "GdVO_4 as a new medium for solid-state lasers: some optical and thermal properties of crystals doped with Nd~(3+), Tm~(3+), and Er~(3+)ions," Quantum Electron., 25, 1162, (1995).