在考慮了「熱透鏡效應」以及「共振腔最佳化」條件後，我們成功的 獲得了一個較為穩定且緊密的「Nd:YVO4/Cr4+:YAG - 被動式 Q-開關 種子雷射」實驗結果，透過更換飽和吸收體的實驗所得到的實驗數據 為漸增的脈衝能量從 22μJ ~ 36μJ；脈衝重複率從 50 kHz 到 25 kHz。
之後 選取最高重複率(初始穿透率 70%飽和吸收體)以及最高峰值功 率(初始穿透率 40%飽和吸收體)，將其經由光纖放大器實驗將其能量 放大所得到的結果分別為，脈衝能量 178μJ,峰值功率 37 kW(T0=70%)；
脈衝能量 192μJ,峰值功率 113 kW(T0=40%)。
由於最大激發功率會受限於光纖的損壞上限極值，過大的激發功率 將造成光纖端面的毀損(如圖 4.4 所述)；因此 我們預期未來如果「光 纖放大器」實驗在相同的實驗架構下，將增益介質由一般傳統 LMA 光纖替換為「光子晶體光纖」(Photonic crystal fiber)，則預期結果將 可以操作在更高的峰值功率狀態而不會產生端面毀損的情形。 由於
「光子晶體光纖」的心蕊孔徑面積較一般傳統 LMA(Large mode area) 光纖大 5.5 倍；且其數值孔徑也更小(0.03)。 由這兩種特點 我們預 期可以在實驗過程中不造成光纖端面毀損的條件下，獲得更高功率的 峰值功率，並且獲得更好的雷射品質。
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圖 4.6 傳統 LMA 光纖與 PCF 截面積圖
圖 4.7 PCF 光纖放大器實驗架構
Traditional DC fiber Photonic crystal fiber
Traditional “Large mode area” fiber Core diameter: 30 μm
Core N.A.: 0.07
Photonic crystal fiber Core diameter: 70 μm
Core N.A.:0.03
Core size 5.5 times to traditional fiber. More important, it’s “single mode”.
Traditional DC fiber Photonic crystal fiber
Traditional “Large mode area” fiber Core diameter: 30 μm
Core N.A.: 0.07
Photonic crystal fiber Core diameter: 70 μm
Core N.A.:0.03
Core size 5.5 times to traditional fiber. More important, it’s “single mode”.
Laser Diode @ 976nm
Dichroic mirror HT@976nm HR@1030~1100nm
0.36m Yb-doped PCF Coupling lens Laser Diode @ 976nm
Dichroic mirror HT@976nm HR@1030~1100nm
0.36m Yb-doped PCF Coupling lens
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參 考 文 獻
[1] J. J. Degnan, “Theory of the optimally coupled Q-switched laser.”
IEEE J.Quantum. , 1989, 25: 214-220.
[2] W. Koechner, Solid-State Laser Engineering, 6th edn. (Springer, Berlin, 2005),Ch.8.
[3] J. Y. Huang, W. Z. Zhuang, W. C. Huang, K. W. Su, C. Hu, K. F.
Huang, and Y. F. Chen, “Comparative studies for Cr4+:YAG crystal and AlGaInAs semiconductor used as a saturable absortor in Q-switched Yb-doped fiber laser”
[4] C. Li, J. Song, D. Shen, N. S. Kim, J. Lu, and K. Ueda,
“Diode-pumped passively Q-switched Nd:GdVO4 lasers operating at 1.06μm wavelength,” Appl. Phys. B 70(4), 471-474 (2000)
[5] W. Koechner, Solid-State Laser Engineering, 6th edn. (Springer, Berlin, 2005),Ch.2.
[6] H. C. Liang, “Investigations and Application of Self-Mode-Locked Lasers”,Ch.6
[7] Y. F. Chen, S. W. Tsai, and S. C. Wang, “High-power diode-pumped Q-switched and mode-locked Nd:YVO4 laser with a Cr4+:YAG saturable absorber,” Opt. Lett. 25(19), 1442-1444 (2000).
[8] J. J. Degnan, D. B. Coyle, and R. B. Kay, “Effect of thermalization on Q-switched lasers properties,” IEEE J. Quantum Electron. 34(5), 887-889 (1998).
[9] G. Xiao, J. H. Lim, S. Yang, E. Van Stryland, M. Bass, and L.Weichman, “Z-scan measurement of the ground and excited state absorption cross sections of Cr4+ in yttrium aluminum garnet,” IEEE J.
64
Quantum Electron. 35(7), 1086-1091 (1999).
[10] G. Xiao, J. H. Lim, S. Yang, E. Van Stryland, M. Bass, and L.Weichman, “Z-scan measurement of the ground and excited state absorption cross sections of Cr4+ in yttrium aluminum garnet,” IEEE J.
Quantum Electron. 35(7), 1086-1091 (1999).
[11] Y.F. Chen, Y.C. Chen, S.W. Chen, Y.P. Lan, “High-power efficient diode-pumped passively Q-switched Nd:YVO4/KTP/Cr4+:YAG eye-safe laser,” Opt. Commun. 234, 337-342 (2004).
[12] N. Hodgson, and H. Weber, Laser Resonators and Beam Propagation, 2nd edn. (Springer, Berlin, 2005), Ch. 5.
[13] W. Koechner, Solid-State Laser Engineering, 6th edn. (Springer, Berlin, 2005), Ch. 7.
[14] N. Hodgson, and H. Weber, Laser Resonators and Beam Propagation, 2nd edn. (Springer, Berlin, 2005), Ch. 8.
[15] Y. F. Chen, T. M. Huang, C. F. Kao, C. L. Wang, and S. C. Wang,
“Optimization in scaling fiber-coupled laser-diode end-pumped lasers to higher power: influence of thermal effect,” IEEE J. Quantum Electron.
33(8), 1424-1429 (1997).
[16] J. H. Campbell, and F. Rainer, “Optical glasses for high-peak-power laser applications,” Proc. of SPIE 1791, 246-255 (1992).
[17] A. Agnesi and S. Dell'Acqua, “High-peak-power diode-pumped passively Q-switched Nd:YVO4 laser,” Appl. Phys. B 76(4), 351–354 (2003).
[18] J. Song, C. Li, N. S. Kim, and K. Ueda, “Passively Q-switched diode-pumped continuous-wave Nd:YAG-Cr4+:YAG laser with high peak
65
power and high pulse energy,” Appl. Opt. 39(27), 4954-4958 (2000).
[19] Y. F. Chen, S. W. Chen, Y. C. Chen, Y. P. Lan, and S. W. Tsai,
“Compact efficient intracavity optical parametric oscillator with a passively Q-switched Nd:YVO4/Cr4+:YAG laser in a hemispherical cavity,” Appl. Phys. B 77, 493-495 (2003).
[20] H. Yu, H. Zhang, Z. Wang, J. Wang, Z. Shao, M. Jiang, and X. Zhang,
“CW and Q-switched laser output of LD-end-pumped 1.06μm c-cut Nd:LuVO4 laser,” Opt. Express 15(6), 3206–3211 (2007).
[21] H. Yu, H. Zhang, Z. Wang, J. Wang, Y. Yu, M. Jiang, and X. Zhang,
“Passively Q-switched laser performance of c-cut Nd:Gd0.63Y0.37VO4
crystal,” Opt. Commun. 281(20), 5199-5201 (2008).
[22] C. Li, J. Song, D. Shen, J. Xu, and K. Ueda, “Diode-pumped CW and passively Q-switched solid-state lasers with an ultra-thin Nd:YVO4
crystal as the gain medium,” Opt. Commun. 186(4-6), 245-250 (2000).
[23] C. Ye, M. Gong, P. Yan, Q. Liu, and G. Chen, “Linearly-polarized single-transverse-mode high-energy multi-ten nanosecond fiber amplifier with 50W average power” Opt. Express 14(17), 7604–7609 (2006).
[24] C. Ye, P. Yan, L. Huang, Q. Liu, and M. Gong, “Stimulated Brillouin scattering phenomena in a nanosecond linearly polarized Yb-doped double-clad fiber amplifier,” Laser Phys. Lett. 4(5), 376-381 (2007).