近年來，摻鈦藍寶石雷射(Ti:sapphire laser)和摻鐿鎢酸釓鉀晶體脈衝放大器(YB:KGW laser)快速發展，兩者差異為平均功率、重複率以及脈衝時寬。摻鈦藍寶石雷射擁有較寬的增益頻寬，可以提供較短時寬的脈衝，但是其平均功率與重複率可控制的範圍有限;而摻鐿鎢酸釓鉀晶體脈衝放大器，因其晶體的特性，可以使得電子在高能階時，存活時間較長，以及激發電子至高能階為連續波雷射(半導體泵浦固體雷射)，能夠持續激發電子至高能階，故其擁有更高的平均功率，同時也擁有較高自由度的重複率調變，但是其缺點為晶體增益頻寬窄，無法提供較短時寬的脈衝。基於上述兩點比較，若將摻鐿鎢酸釓鉀晶體脈衝放大器窄頻寬的問題解決，可以同時得到兩台雷射本身的優勢，所以，以頻譜擴展的方式能夠有效的將時間脈衝壓縮。
本論文探討的內容為使用摻鐿鎢酸釓鉀晶體脈衝放大器經過倍頻晶體後產生的可見光，將此光源利用二次頻譜擴展的方式從 123.9 飛秒壓縮到 12.7 飛秒，將峰值功率從 4.6 十億瓦提升至 22.2 十億瓦以及觀察下一級轉換極限脈衝寬為 6 飛秒的結果，同時量測每一次頻譜擴展後的頻譜、雷射光束品質(M2)、空間頻譜均勻性、時間上的脈衝形狀以及長期穩定性。

In recent years, Ti: sapphire laser and YB: KGW laser have developed rapidly. The difference between the two lasers is the average power, the repetition rate, and the pulse duration. Ti: sapphire laser has a wide gain bandwidth and can provide short pulse duration. However, the range of controllable average power and repetition rate is limited. The YB: KGW laser, because of the characteristics of the crystal, can make the electrons longer lifetimes at high energy levels. And the continuous wave laser (semiconductor-pumped solid-state laser) can continuously excite electrons to high energy levels, so it has a higher average power. It also has a higher degree of controllable repetition rate modulation, but its disadvantage is that the crystal gain has a narrow bandwidth and cannot provide a short pulse duration. Based on the comparison of the above two points, if the problem of the narrow bandwidth of the YB: KGW laser is solved, the advantages of the two lasers can be obtained at the same time. Therefore, the pulse can be effectively compressed by spectral broadening.
The content discussed in this thesis is the use of the visible light generated by the YB: KGW laser after passing through the frequency-doubling crystal. Compressing this light source from 123.9 femtoseconds to 12.7 femtoseconds using twice spectral broadening, and increases peak power from 4.6 gigawatts to 22.2 gigawatts, and observe the result that the next-level transform-limited pulse duration is 6 femtoseconds, and measure the spectrum, laser beam quality (M2), spatial-spectral homogeneity, pulse shape in time-domain and long-term stability after each spectral broadening.

1. O. Dühr, E. T. J. Nibbering, G. Korn, G. Tempea, and F. Krausz, “Generation of intense 8-fs pulses at 400 nm,” Opt. Lett. 24, 34–36 (OSA, 1999).
2. Y.-Y. Liu, K. Zhao, P. He, H.-D. Huang, H. Teng, and Z.-Y. Wei, “High-Efficiency Generation of 0.12 mJ, 8.6 Fs Pulses at 400nm Based on Spectral Broadening in Solid Thin Plates,” Chinese Physics Letters 34, 074204 (IOP Publishing, 2017).
3. F. Hu, Q. Zhang, J. Cao, Z. Hong, W. Cao, and P. Lu, “Generation of 5.2 fs, energy scalable blue pulses,” Opt. Lett. 47, 389–392 (2022).
4. H.-T. Chang, M. Zürch, P. M. Kraus, L. J. Borja, D. M. Neumark, and S. R. Leone, “Simultaneous generation of sub-5-femtosecond 400 nm and 800 nm pulses for attosecond extreme ultraviolet pump–probe spectroscopy,” Opt. Lett. 41, 5365–5368 (2016).
5. I. Procino, R. Velotta, C. Altucci, S. Amoruso, R. Bruzzese, X. Wang, V. Tosa, G. Sansone, C. Vozzi, et al., “Hollow-fiber compression of visible, 200 fs laser pulses to 40 fs pulse duration,” Opt. Lett. 32, 1866–1868 (2007).
6. D. Descamps, F. Guichard, S. Petit, S. Beauvarlet, A. Comby, L. Lavenu, and Y. Zaouter, “High-power sub-15 fs nonlinear pulse compression at 515 nm of an ultrafast Yb-doped fiber amplifier,” Opt. Lett. 46, 1804–1807 (2021).
7. V. Hariton, A. Bin Wahid, G. Figueira, K. Fritsch, and O. Pronin, “Multipass spectral broadening and compression in the green spectral range,” Opt. Lett. 47, 1246–1249 (2022).
8. Shiner AD, Trallero-Herrero C, Kajumba N, Bandulet H-C, Comtois D, Légaré F, et al. “Wavelength scaling of high harmonic generation efficiency.” Phys Rev Lett. 2009;103(7):073902.
9. K. W. DeLong, Rick Trebino, and Daniel J. Kane “Comparison of ultrashort-pulse frequency-resolved-optical-gating traces for three common beam geometries” Opt. Soc. Am. B Vol. 11, Issue 9, pp. 1595-1608 (1994)
10. S. B. Park, K. Kim, W. Cho, S. I. Hwang, I. Ivanov, C. H. Nam, K.T. Kim“Direct sampling of a light wave in air” Optica 5, 402-408 (2018).
11. Fan Xiao, Xiaohui Fan, Li Wang, Dongwen Zhang, Jianhua Wu, Xiaowei Wang, Zengxiu Zhao“Generation of Intense Sub-10 fs Pulses at 385nm” CHIN. PHYS. LETT 37, 114202 (2020).
12. Jun Liu, Kotaro Okamura, Yuichiro Kida, Takahiro Teramoto, Takayoshi Kobayashi “Clean sub-8-fs pulses at 400 nm generated by a hollow fiber compressor for ultraviolet ultrafast pump-probe spectroscopy” OPTICS EXPRESS 18, 20645-20650 (2010)
13. Jun Liu, Yuichiro Kida, Takahiro Teramoto, Takayoshi Kobayashi “Generation of stable sub-10 fs pulses at 400 nm in a hollow fiber for UV pump-probe experiment” OPTICS EXPRESS 18, 4664-4672 (2010)
14. Chih-Hsuan Lu, Tobias Witting, Anton Husakou, Marc J.J. Vrakking, A. H. Kung, Federico J. Furch “Sub-4fs laser pulses at high average power and high repetition rate from an all-solid-state setup” OPTICS EXPRESS 26, 8941-8956 (2018)
15. Martin Kaumanns, Vladimir Pervak, Dmitrii Kormin, Vyacheslav Leshchenko, Alexander Kessel, Moritz Ueffing, Yu Chen, Thomas Nubbemeyer “Multipass spectral broadening of 18 mJ pulses compressible from 1.3 ps to 41 fs” Opt. Lett. 43, 5877–5880 (2018).
16. John C. Travers , Teodora F. Grigorova , Christian Brahms , Federico Belli “High-energy pulse self-compression and ultraviolet generation through soliton dynamics in hollow capillary fibres” Nat. Photonics, 13, 547–554 (2019)
17. P. Dombi, V. S. Yakovlev, K. O'Keeffe, T. Fuji, M. Lezius, G. Tempea, “Pulse compression with time-domain optimized chirped mirrors” Opt. Express,13(26), 10888-10894 (2005).
18. Robert Klas, Alexander Kirsche, Martin Gebhardt, Joachim Buldt, Henning Stark, Steffen Hädrich, Jan Rothhardt, Jens Limpert “Ultra-short-pulse high-average-power megahertz-repetition-rate coherent extreme-ultraviolet light source” PhotoniX (2021) 2:4
19. PHYS 630: Advanced Optics (Fall 2008) http://nicadd.niu.edu/~piot/phys_630/Materials.html
20. S. B. Park, K. Kim, W. Cho, S. I. Hwang, I. Ivanov, C. H. Nam, K.T. Kim“Direct sampling of a light wave in air: supplementary material” Optica supplementary material